Source string | Question string | Answer string | Question_type string | Referenced_file(s) string | chunk_text string | expert_annotation string | specific to paper string | Label int64 |
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IPAC | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | $$ \\frac { \\epsilon _ { x , I D s } } { \\epsilon _ { x } } = \\frac { 1 } { 1 + \\displaystyle \\frac { I _ { 2 , I D s } } { I _ { 2 , d i p . } } } $$ From Equation 1 we can also express the energy loss per turn as a function of $I _ { 2 , d i p }$ : $$ U _ { 0 } = P _ { 0 } / I \\approx \\frac { C _ { \\gamma } } { 2 \\pi } E ^ { 4 } I _ { 2 , d i p } $$ with $P _ { 0 }$ the power radiated in the nominal lattice (without IDs), $r _ { 0 }$ the classical electron radius and $C _ { \\gamma } = \\frac { 4 \\pi } { 3 } \\frac { r _ { 0 } } { ( m _ { 0 } c ^ { 2 } ) ^ { 3 } } ,$ Ôºö Now combining Equations 3, 8, and 10, the approximated expression for the emittance variation becomes : | augmentation | NO | 0 |
IPAC | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | EXPERIMENTAL RESULTS The filter transmission functions, an example of which is presented on Fig. 4 left, are far from the desired $1 0 0 \\mathrm { n m }$ bandwidth ideals. This fact introduces an ambiguity in the transformation from the measured induced voltage to the beam distribution $U _ { i } \\to \\rho ( \\lambda )$ . Therefore, we fit the data by repeatedly taking guesses of the distribution: $$ { \\frac { \\mathrm { e l e v a t e d } } { \\mathrm { q u i e t } } } = { \\frac { \\int T ( \\lambda ) F ( \\lambda ) / \\lambda ^ { 2 } d \\lambda } { \\int T ( \\lambda ) 1 / \\lambda ^ { 2 } d \\lambda } } $$ where $F ( \\lambda ) = N \\left| \\rho ( \\lambda ) \\right| ^ { 2 }$ is the Fano factor spectral density and $T ( \\lambda )$ is the transmission function of the transport line, including the photodiode responsivity. Comparison of the theoretical predictions and experimental results is presented on Fig. 4 right. Here the combined reflectivity of the light channel is taken to be $8 0 \\pm 1 0 \\%$ , and the transverse beam shape - round Gaussian. Red values are the predicted voltages, induced by the radiation passed through the filters; blue values are the measured voltages. Two errors include common and individual multipliers at all points. Individual errors are depicted at both experimental and theoretical curves as error bars, while the common multiplier and systematic errors are shown as bands. | augmentation | NO | 0 |
IPAC | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | Patterned coatings had been developed elsewhere [5] to suppress eddy currents and, thereby, allow thinner coatings. Following this idea, we developed a patterned coating design with $2 { - } 3 \\Omega / \\mathrm { s q }$ and low field attenuation. The impedance and field attenuation were analyzed using CST Studio [6]. We partnered with Kyocera to fabricate four patterned chambers, shown in Fig. 3. The dark areas are Ti-coated to carry the image current. The light areas are uncoated and serve to mitigate the eddy current effects. A special fourpoint probe was developed, shown in Fig. 4, to directly measure the surface resistance, using $\\boldsymbol { R _ { s } } [ \\Omega ] =$ $4 . 5 2 6 V [ m V ] / I \\left[ m V \\right]$ . Acceptance testing showed that the chambers gave $3 { - } 4 ~ \\Omega / \\mathrm { s q }$ , which is close to the design. The first chamber was installed in Jan 2023 and performed satisfactorily for three months of operation. The second and third chambers were installed at the beginning of the Dark Time. The final performance was verified after vacuum conditioning, described in the next section. | augmentation | NO | 0 |
IPAC | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | For a magnet with small gradient of its fringe field, the excitation efficiency drops down mostly due to vertical size increase of the $\\mathrm { H } ^ { 0 }$ beam at the interaction point (see Fig. 5) Beam size increases over the drift length $_ { \\mathrm { L } = 3 0 \\mathrm { c m } }$ due to initial angular spread $\\sigma \\colon r = { \\sqrt { r _ { 0 } ^ { 2 } + L ^ { 2 } \\sigma ^ { 2 } } }$ . Figure 5 can be calculated using the output angular spread as: $\\sigma ^ { 2 } \\to \\sigma _ { 0 } ^ { 2 } + \\sigma _ { \\phi } ^ { 2 }$ The initial rms beam size is considered to be $r _ { 0 } { = } 0 . 5 ~ \\mathrm { m i n }$ Larger $\\mathrm { \\Delta H ^ { 0 } }$ beam size requires a larger laser spot with the same power density, thus a higher peak laser power. Figure 6 represents the impact of a vertically oriented magnetic stripping field on the excitation efficiency of LACE. | augmentation | NO | 0 |
IPAC | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | In this paper, we propose an improved lattice that takes chromatic effects into account and explore a method to compensate it. Simulations has been performed with the tracking program ASTRA [9] and the results demonstrate that a transverse emittance ratio of approximately 840 can be achieved by using the proposed method. THEORY OF FLAT BEAM GENERATION Considering the cathode is immersed in solenoid fields, at the exit of the solenoid, the beam is coupled transversely and has a net angular momentum. The coupling of horizontal and vertical coordinates and angles are described by [10]: $$ \\begin{array} { r } { \\left[ \\begin{array} { l } { y _ { 0 } } \\\\ { y _ { 0 } ^ { \\prime } } \\end{array} \\right] = \\left[ \\begin{array} { l l } { 0 } & { - \\beta } \\\\ { \\frac { 1 } { \\beta } } & { 0 } \\end{array} \\right] \\cdot \\left[ \\begin{array} { l } { x _ { 0 } } \\\\ { x _ { 0 } ^ { \\prime } } \\end{array} \\right] = F \\cdot \\left[ \\begin{array} { l } { x _ { 0 } } \\\\ { x _ { 0 } ^ { \\prime } } \\end{array} \\right] , } \\end{array} | augmentation | NO | 0 |
IPAC | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | In this paper, we present the fully detailed design of XT72, along with the fabrication, RF tuning and high-power test results of the first XT72 structure. The results demonstrate its ability to operate at a gradient of ${ 8 0 } \\mathrm { M V / m }$ with a lower BDR. DESIGN We choose $2 \\pi / 3$ phase advance per cell as the working mode for a better trade off between shunt impedance and filling time. The aperture of the cell is a crucial variable; the smaller it is, the higher the shunt impedance and longer the filling time, but the wakefield is more intense. The apertures of the CG structure are selected to be in the range of 3.12 mm to $3 . 9 2 \\mathrm { m m }$ , resulting in an average aperture of $3 . 5 2 \\mathrm { m m }$ The shunt impedance of XT72 is similar to that of XC72. The RF properties of first, middle and end cell are shown in Tab. 1, the other cells’ properties can be interpolated from these values. The $\\nu _ { g } / c$ denotes the group velocity relative to the speed of light, $r / Q$ represents the shunt impedance over quality factor, $E _ { s }$ denotes the surface electric field, $E _ { a }$ represents the accelerating gradient of the cell, $H _ { s }$ denotes the surface magnetic field, and $S _ { c }$ is the modified Poynting factor [5]. | augmentation | NO | 0 |
IPAC | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | Table: Caption: Table 1: Lattice performance comparison between the standard lattice (STD) and the mini- $\\beta$ lattice (MB7). Tracking simulations are done with errors and corrections. The lifetime is calculated for $1 0 \\mathrm { p m }$ vertical emittance and $Z / n { = } 0 . 5 2 \\Omega$ . The brilliance is calculated using the SRW code [4] for a CPMU at the center of the straight section. Body: <html><body><table><tr><td>Units</td><td>STD</td><td>MB7</td></tr><tr><td colspan="3">Lattice Characteristics</td></tr><tr><td>Lifetime</td><td>h 31.6 ± 1</td><td>23.9 ± 1.6 -9.1 ± 0.7</td></tr><tr><td>DA(δp=0) IE</td><td>mm -9.4 ± 0.4 % 96.7 ± 1</td><td>96.8 ± 1</td></tr><tr><td></td><td colspan="2">Brilliance [10²1 photons/s/0.1%/mm²/mrad²]</td></tr><tr><td>12.6 keV</td><td>6.27</td><td>7.46</td></tr><tr><td>50.0 keV</td><td>1.07</td><td>2.34</td></tr><tr><td>100.0keV</td><td>0.143</td><td>0.334</td></tr></table></body></html> It should be noted that the brilliance increase is most visible at higher energies. More than $8 0 \\%$ of this gain is obtained with the reduction of the vertical $\\beta$ -function and consequently the reduction of the IVU gap. This is explained by the fact that the tuning range of all harmonic extends to lower energy and eventually overlap thanks to the lower IVU gap. In this configuration, it should be possible to work on a higher order harmonic for a given energy and increase the brilliance by working on the high brilliance low energy end of the harmonic rather than the low brilliance high energy end of the harmonic. | augmentation | NO | 0 |
IPAC | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | Figure 5 shows the resulting electric field profiles on the $z$ -axis along the first two cells at di!erent cell $\\# 0$ dimensions. Shorter gaps imply greater peaks of gradient, thus greater surface fields, although smaller than in regular cells where fields are more critical (Kilpatrick’s limit). It is also worth mentioning that a shorter gap produces a smaller dipole kick and requires a smaller angle of correction between opposite drift tube faces. EFFICIENCY IMPROVEMENTS Conventional IH-DTL structures assemble the stems over equally-long girders on the top and bottom of the cavity, and undercuts are machined on them. In our model of Fig. 1, the end of the second stem makes a last elliptical arc to imitate the geometry of conventional girders. However, such arc does not play any role neither in the capacitance between drift tubes nor the auto-inductance of the cavity. For this reason, we have proposed to remove the last arc and finish the stem in a vertical wall as depicted in Fig. 6. This modification requires a slight increment of $2 \\mathrm { m m }$ on the undercut length $L _ { c u t }$ to retune the eigenmode frequency to ${ 7 5 0 } \\mathrm { M H z }$ Additional refinement on the dipole electric field correction must be made due to the new alteration of the opposing stems asymmetry. The overall e"ciency performance, in this case, is improved from a shunt impedance of 236 to $2 4 8 \\ : \\mathrm { M } \\Omega / \\mathrm { m }$ Such modification in the geometry of both ends of the cavity entails savings of $4 8 0 \\mathrm { W }$ peak power. | 1 | NO | 0 |
IPAC | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | Two optimization functions were defined. The first with an objective of minimization was the design’s volume $f _ { 1 } ( k )$ : $$ f _ { 1 } ( k ) = \\left[ k _ { 1 } ( 2 k _ { 2 } - 1 ) ( 2 k _ { 1 } + t ) + k _ { 1 } ^ { 2 } ( 2 k _ { 2 } + 2 ) + 4 8 k _ { 1 } \\right] 2 d k _ { 3 } , $$ where $t$ is the groove’s width and $d$ is the thickness of the SC layer. The variable $k$ represents the three design parameters: $k _ { i }$ with $i = 1 , 2 , 3$ . The second function with an objective of maximization was the field integral per unit wavelength $f _ { 2 } ( k )$ defined longitudinally on the symmetry axis $( x \\ =$ $x _ { 0 } , y = y _ { 0 } , z = z )$ as: $$ f _ { 2 } ( k ) = \\frac { \\int _ { z _ { i } } ^ { z _ { j } } | B _ { y } ( x = x _ { 0 } , y = y _ { 0 } , z ) | d z } { \\# \\lambda } . | 1 | NO | 0 |
Expert | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | $$ { \\bf J } ( { \\bf r } , \\omega ) = \\frac { q } { 2 \\pi } { ( 2 \\pi \\sigma _ { x } ^ { 2 } ) } ^ { - 1 / 2 } \\mathrm { e } ^ { - x ^ { 2 } / 2 \\sigma _ { x } ^ { 2 } } \\mathrm { e } ^ { - i k _ { y } y } \\widehat { { \\bf y } } $$ with $k _ { y } = \\omega / \\nu$ . Using this expression, the electromagnetic field was calculated via Maxwell’s equations for linear, nonmagnetic materials. As this is a 2D problem, the transverse-electric mode $E _ { z }$ decouples from the transverse-magnetic mode $H _ { z } ,$ where only the latter is relevant here. A typical 2D-FDFD simulation took 1 s on a common laptop, and the algorithm needed about 500 iterations to converge to a stable maximum. Simulated Radiation Power. From the simulated electromagnetic field, we calculate the total energy $W$ radiated by a single electron per period $a$ of the grating. In the time domain, this would correspond to integrating the energy flux $\\mathbf { \\boldsymbol { s } } ( \\mathbf { \\boldsymbol { r } } , \\ t )$ through the area surrounding the grating over the time it takes for the particle to pass over one period of the grating. In the frequency domain, one needs to integrate $\\mathbf { \\Delta } \\mathbf { S } ( \\mathbf { r } , \\omega )$ through the area around one period over all positive frequencies, that is,36 | augmentation | NO | 0 |
Expert | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | 3D Simulations. 3D finite-element-method (FEM) frequency-domain simulations were performed in COMSOL to analyze effects originating from the finite height of the structure and beam. The structures were assumed to be $1 . 5 \\mu \\mathrm { m }$ high on a flat silicon substrate (Figure 1b). The spectral current density had a Gaussian beam profile of width $\\sigma = 2 0$ nm: $$ \\mathbf { J } ( \\mathbf { r } , \\omega ) = \\frac { - e } { 2 \\pi } \\big ( 2 \\pi \\sigma ^ { 2 } \\big ) ^ { - 1 } \\mathrm { e } ^ { - \\big ( x ^ { 2 } + z ^ { 2 } \\big ) / 2 \\sigma ^ { 2 } } \\mathrm { e } ^ { - i k _ { y } y } \\widehat { \\mathbf { y } } $$ Experimental Setup. The experiment was performed within an FEI/Philips XL30 SEM providing an $1 1 \\mathrm { \\ n A }$ electron beam with $3 0 \\mathrm { \\ k e V }$ mean electron energy. The structure was mounted to an electron optical bench with full translational and rotational control. The generated photons were collected with a microfocus objective SchaÃàfter+Kirchhoff 5M-A4.0-00-STi with a numerical aperture of 0.58 and a working distance of $1 . 6 ~ \\mathrm { m m }$ . The objective can be moved relative to the structure with five piezoelectric motors for the three translation axes and the two rotation axes transverse to the collection direction. The front lens of the objective was shielded with a fine metal grid to avoid charging with secondary electrons in the SEM, which would otherwise deflect the electron beam, reducing its quality. The collected photons were focused with a collimator into a ${ 3 0 0 } { - } \\mu \\mathrm { m }$ -core multimode fiber guiding the photons outside the SEM, where they were detected with a NIRQuest $^ { \\cdot + }$ spectrometer. | augmentation | NO | 0 |
Expert | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | allows to design the spectrum $( \\omega )$ , spatial distribution $\\mathbf { \\Pi } ( \\mathbf { r } )$ , and polarization (e) of radiation by favoring one kind $| \\mathbf { e } { \\cdot } \\mathbf { E } ( \\mathbf { r } , \\omega ) |$ and penalizing others, $- | \\mathbf { e } ^ { \\prime } { \\boldsymbol { \\cdot } } \\mathbf { E } ( \\mathbf { r } ^ { \\prime } , \\omega ^ { \\prime } ) |$ , with possibly orthogonal polarization $\\mathbf { e ^ { \\prime } }$ . Lifting the periodicity constraint opens the space to complex metasurfaces, which would for example enable designs for focusing or holograms.18,22‚àí27,40 Future efforts could also target the electron dynamics to achieve (self-)bunching and, hence, coherent enhancement of radiation. In that case, the objective function would aim at the field inside the electron channel rather than the far-field emission. This would favor higher quality factors at the cost of lower out-coupling efficiencies. However, direct inclusion of the electron dynamics through an external multiphysics package proves challenging as our inverse design implementation requires differentiability of the objective function with respect to the design parameters. Instead, one may choose to use an analytical expression for the desired electron trajectory or an approximate form for the desired field pattern. | augmentation | NO | 0 |
Expert | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | A 200-period-long version of the inverse-designed structure was fabricated by electron beam lithography $\\bar { ( } 1 0 0 \\ \\mathrm { k V } )$ and cryogenic reactive-ion etching of $1 - 5 \\Omega \\cdot \\mathrm { c m }$ phosphorus-doped silicon to a depth of $1 . 3 \\big ( 1 \\big ) \\mathsf { \\bar { \\mu } m }$ .35 The surrounding substrate was etched away to form a $5 0 ~ \\mu \\mathrm { m }$ high mesa (Figure 2a). We note that unlike in most previous works the etching direction is here perpendicular to the radiation emission, enabling the realization of complex 2D geometries. The radiation generation experiment was performed inside a scanning electron microscope (SEM) with an 11 nA beam of $3 0 \\mathrm { \\ k e V }$ electrons. The generated photons were collected with an objective (NA 0.58), guided out of the vacuum chamber via a $3 0 0 ~ \\mu \\mathrm { m }$ core multimode fiber and detected with a spectrometer (Figure 2b and Methods). RESULTS We compare the emission characteristics of the inversedesigned structure to two other designs: First, a rectangular 1D grating with groove width and depth of half the periodicity $a _ { \\mathrm { { ; } } }$ , similar to the one used in refs 6 and 36. And second, a dual pillar structure with two rows of pillars, $\\pi$ -phase shifted with respect to each other, and with a DBR on the back. This design was successfully used in dielectric laser acceleration, the inverse effect of SPR. $\\mathbf { \\lambda } ^ { 3 0 , 3 2 , 3 3 , 3 5 , 3 7 - } 3 9$ It further represents the manmade design closest to our result of a computer-based optimization. | augmentation | NO | 0 |
Expert | Why does the inverse-designed grating exhibit higher efficiency than a conventional rectangular grating? | Because the photonic inverse design tailors the dielectric distribution to maximize directional emission and resonant coupling for the target wavelength. | Reasoning | haeusler-et-al-2022-boosting-the-efficiency-of-smith-purcell-radiators-using-nanophotonic-inverse-design.pdf | DISCUSSION Comparing the measured emission spectrum of the inverse design to its simulated profile shows that the observed emission was not as powerful and spectrally broader. We identify two causes: First, the electron beam current deteriorates as the beam diverges, where electrons hit the boundaries of the channel and are lost. By measuring the current after the structure, we determined an effective current $I _ { \\mathrm { e f f } }$ for each design (Figure 3e and Figure S2). The effective current is smallest for the dual pillar design, which has the narrowest channel, and largest for the single-sided rectangular grating. Another factor that reduces the efficiency of the inversedesigned structure are the deviations of the fabricated structure from its design. Figure 4 shows that the structure was not perfectly vertically etched but has slightly conical features. This leads to a reduction of the quality factor of the inversedesigned structure, which is reflected in a less powerful $( - 6 7 \\% )$ and more broadband emission of radiation. By contrast, the efficiencies of the dual pillar structure and the rectangular grating are expected to be less affected by conical features due to their lack of pronounced resonance. | augmentation | NO | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | Masks were made with hole diameters of 3mm and 5mm, to investigate decoherence caused by possible phase fluctuations across a given hole. Observations were made with integration times (frame times) of 1 ms and 3 ms, to investigate decoherence by phase variations in time. Thirty frames are taken, each separated by 1 sec. We estimate the pixel size in the CCD referenced to the source plane of 0.138 arcsec/pixel, using the known hole separations (baselines), and the measured fringe spacings, either in the image itself, or in the Fourier transformed u,v distribution. IV. STANDARD PROCESSING AND RESULTS A. Images Figure 3 shows two images made with the 3-hole mask, one with 3 mm holes and one with 5 mm holes. Any three hole image will show a characteristic regular grid diffraction pattern, modulated by the overall power pattern of the individual holes (Thyagarajan $\\&$ Carilli 2022). This power pattern envelope (the ‚Äö√Ñ√¥primary beam‚Äö√Ñ√¥ for the array elements), is set by the hole size and shape, which, for circular holes with uniform illumination, appears as an Airy disk. The diameter of the Airy disk is $\\propto \\lambda / D$ , where $\\lambda$ is the wavelength and $D$ is the diameter. Also shown in Figure 3 are the Fourier transforms of the images (see Section IV B). The point here is that the size of the uv-samples decreases with increasing beam size = decreasing hole size. The primary beam power pattern (Airy disk) multiples the image-plane, which then corresponds to a convolution in the uv-plane. So a smaller hole has a larger primary beam and hence a smaller convolution kernel in the Fourier domain. | 1 | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | D. 3ms vs 1ms coherences: 5 hole data We consider the affect of the integration time on coherence and closure phase on the 5-hole data (see Section VII for further analysis with other masks). Figure 22 shows the coherence at 3 ms vs 1 ms integrations. The 3 ms coherences are lower by about 2 - 10%. The rms of 3 ms coherences are much higher by factors 2 to 7. The explanation of the Figure 22 is Figure 23, which shows the time series of coherences for 3 ms vs 1 ms. Two things occur: (i) the coherence goes down by up to 8%, and (ii) the rms goes way up with 3 ms, by up to a factor 7. The increased rms in 3 ms data appears to be due to ‚Äö√Ñ√¥dropouts‚Äö√Ñ√¥, or records when the coherence drops by up to $2 0 \\%$ . Figure 24 shows the closure phases for $3 \\mathrm { m s }$ averaging vs. 1 ms averaging. The differences in closure phases are small, within a fraction of a degree. The rms scatter is slightly larger for $3 \\mathrm { m s }$ , but again, not dramatically. Hence, closure phase seems to be more robust to averaging time, than coherence itself. | 4 | Yes | 1 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | We explore radii of 3, 5, 7, and 9 pixels, considering coherences and closure phases. Figure 19 shows the closure phases versus the u,v aperture radius. The closure phase values tend toward smaller values with increasing aperture size. The RMS scatter decreases substantially with aperture size until 7pix radius. Figure 20 shows the coherences for different u,v aperture radii. The coherences vary slightly, typically less than $2 \\%$ . The RMS of the coherences are relatively flat, or slightly declining, to 7 pixel radius, with a few then increasing at 9 pixels. C. 3 mm vs 5 mm coherences We consider the affect of the size of the hole in the non-redundant mask on coherence and closure phase. Figure 21 shows the coherence for a 5-hole mask with $3 \\mathrm { m m }$ and 5 mm holes. The 5 mm data fall consistently below the equal coherence line, implying lower coherence by typically 5% to $1 0 \\%$ . Also shown is the RMS for the coherence time series. The RMS scatter for the 5 mm holes is higher, more than a factor two higher in some cases. Lower coherence for larger holes may indicate phase gradients across holes. A hole phase gradient is like a pointing error which implies mismatched primary beams in the image plane and may lead to decoherence. | 4 | Yes | 1 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | Next we pad and center the data so that the centre of the Airy disk-like envelope of the fringes is in the centre of a larger two-dimensional array of size $2 0 4 8 \\times 2 0 4 8$ . To find the correct pixel to center to we first smooth the image with a wide (50 pixel) Gaussian kernel, then select the pixel with highest signal value. The Gaussian filtering smooths the fringes creating an image corresponding approximately to the Airy disk. Without the filtering the peak pixel selected would be affected by the fringe position and the photon noise, rather than the envelope. Off-sets of the Airy disk from the image center lead to phase slopes across the u,v apertures. To calculate the coherent power between the apertures, we make use of the van Cittert‚Äö√Ñ√¨Zernike theorem that the coherence and the image intensity are related by a Fourier transform. We therefore compute the two-dimensional Fourier transform of the padded CCD frame using the FFT algorithm. Amplitude and phase images of an example Fourier transform are shown in Figure 5. Distinct peaks can be seen in the FFT corresponding to each vector baseline defined by the aperture separations in the mask. | 2 | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | Table I also lists the gains derived after image averaging, with and without Airy disk centering. In this case, the gains are essentially unchanged (within $1 \\%$ ), relative to the mean from the time series (row 1). This similarity for gain results from data that clearly involved decoherence of the visibilities themselves lends confidence that the derived illumination correction (the ‚Äôgains‚Äô), are correct. Table: Caption: TABLE I. Gains derived from the self-calibration process for a 5-hole mask. Body: <html><body><table><tr><td>G0</td><td>G1</td><td>G2</td><td>G3</td><td>G4</td><td>œÉ/cells p</td><td>n</td></tr><tr><td>Mean of best-fits in time series 7.35 RMS in time series 0.067</td><td>8.43 0.045</td><td>8.40</td><td>9.37 0.029 0.027 0.034</td><td>9.11 4.88</td><td>74.66 0.9</td><td>0.66 0.42 0.13</td></tr><tr><td>Sum of 3O frames with no centering 7.45</td><td>8.50</td><td>8.47</td><td>9.35</td><td>9.15</td><td>49.1</td><td>0.22 0.15</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Sum of 30 frames with Airy centering 7.41</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td>8.45</td><td>8.50</td><td>9.37</td><td>9.13</td><td>68.8</td><td>0.37 0.58</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></table></body></html> Table: Caption: Body: <html><body><table><tr><td>Baseline</td><td>5-hole Coherence</td><td>RMS</td><td>3-hole Coherence</td><td>RMS</td><td>No Center Airy Center</td><td></td></tr><tr><td>0-1</td><td>0.793</td><td>0.0030</td><td>0.816</td><td>0.0050</td><td>0.67</td><td>0.75</td></tr><tr><td>0-2</td><td>0.972</td><td>0.0079</td><td>0.989</td><td>0.0088</td><td>0.74</td><td>0.93</td></tr><tr><td>0-3</td><td>0.945</td><td>0.0130</td><td></td><td></td><td>0.70</td><td>0.90</td></tr><tr><td>0-4</td><td>0.840</td><td>0.0089</td><td></td><td></td><td>0.67</td><td>0.80</td></tr><tr><td>1-2</td><td>0.645</td><td>0.0048</td><td>0.691</td><td>0.0073</td><td>0.42</td><td>0.61</td></tr><tr><td>1-3</td><td>0.875</td><td>0.0056</td><td></td><td></td><td>0.66</td><td>0.84</td></tr><tr><td>1-4</td><td>0.993</td><td>0.0030</td><td></td><td></td><td>0.90</td><td>0.97</td></tr><tr><td>2-3</td><td>0.933</td><td>0.0014</td><td></td><td></td><td>0.87</td><td>0.91</td></tr><tr><td>2-4</td><td>0.734</td><td>0.0028</td><td></td><td></td><td>0.59</td><td>0.70</td></tr><tr><td>3-4</td><td>0.938</td><td>0.0023</td><td></td><td></td><td>0.86</td><td>0.92</td></tr></table></body></html> TABLE II. Column 2 and 3: mean coherences and RMS scatter for the time series of measurements for the 10 baselines in the 5-hole mask, after Airy centering. Column 4 and 5 lists the same for the 3-hole data. Column 6 lists the coherence derived by first summing all of the frames together, then doing the Fourier transform, without any image centering. Column 7 lists the same but after Airy disk centering. D. Visibility and Closure Phases | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | ‚Ä¢ The outlier dataset is the 5-hole 3ms data (yellow). This data set also has dropouts (see also Figure 23), but further, all of the points appear low, with a mean value substantially lower than all the other data sets, and with the largest rms scatter: $1 6 8 \\pm 1 1$ . Hence, comparing the 1ms data (5 and 3 holes), to the 3ms data (2 and 3 holes), it would appear that the primary effect of longer integration time is to increase the scatter, and cause a few substantial dropouts, which lowers the mean amplitude slightly. But most amplitudes are consistent between 1ms and 3ms frame times, leading to the consistency between the 2-hole 3ms source size calculation and the 5-hole 1ms result. The 5-hole 3ms data is anomalous, in that it has the highest scatter, including dropouts, and a 7% lower overall mean. We speculate that the turbulence or other phase corrupting factors in the laboratory (eg. mirror vibrations), were different at the time of the 5-hole 3ms experiment. Further experiments are planned to explore this issue. As a final pedagogic exercise, we ask: what happens when, for a given baseline, two fringes of equal amplitude but different phase ${ } = { }$ position on detector) are summed during a single measurement, as would occur, for instance, if during the frame integration time there is a phase perturbation leading to a rigid shift of the fringe. Figure 31 shows the profile through a vertical fringe from the 2-hole data, as well as the same profile after shifting the frame by $1 / 4$ of the fringe separation, then summing and scaling by a factor $1 / 2$ . The result is not a smearing or broadening of the fringe, nor a change in fringe spacing, but a change in the contrast, or the ratio of the maximum to minimum values. This behaviour is the basis for the historical definition of the fringe coherence, or visibility $= ( \\mathrm { I } _ { \\mathrm { m a x } } - \\mathrm { I } _ { \\mathrm { m i n } } ) / ( \\mathrm { I } _ { \\mathrm { m a x } } + \\mathrm { I } _ { \\mathrm { m i n } } )$ (Michelson 1890; Monnier 2003). | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | I. INTRODUCTION We consider the measurement of the ALBA synchrotron electron beam size and shape using optical interferometry with aperture masks. Monitoring the emittance of the electron beam is important for optimal operation of the synchrotron light source, and potentially for future improved performance and real-time adjustments. There are a number of methods to monitor the size of the electron beam, including: (i) LOCO, which is a guiding magnetic lattice analysis incorporating the beam position monitors, (ii) X-ray pinholes (Elleaume et al 1995), and (iii) Synchrotron Radiation Interferometry (SRI). Herein, we consider optical SRI, which can be done in real time without affecting the main beam. Previous measurements using SRI at ALBA have involved a two hole Young‚Äôs slit configuration, with rotation of the mask in subsequent measurements to determine the two dimensional size of the electron beam, assuming a Gaussian profile (Torino & Iriso 2016; Torino & Iriso 2015). Such a two hole experiment is standard in synchrotron light sources (Mitsuhasi 2012; Kube 2007), and has been implemented at large particle accelerators, including the LHC (Butti et al. 2022). Four hole square masks have been considered for instantaneous two dimensional size characaterization, but such a square mask has redundant spacings which can lead to decoherence, and require a correction for variation of illumination across the mask (Masaki & Takano 2003; Novokshonov et al. 2017; see Section VI). Non-redundant masks have been used in synchrotron X-ray interferometry, but only for linear (one dimensional grazing incidence) masks (Skopintsev et al. 2014). | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | B. Processing Errors: Gaussian Random Approximation Beyond photon statistics, there are a number of processing steps that affect the resulting coherences, and hence the fit to the source size, including: uv-aperture size, bias subtraction, image centering, and others. In this section, we perform modeling of the uv-data to get an estimate of what level of errors in the coherences could lead to the measured scatter in the final results, assuming a Gaussian random distribution for the various errors over time. Systematic errors with time are considered below. While not strictly rigorous (the modeling does not include effects related to eg. the edges of the CCD or bias subtraction), this uv-model approach does provide a rough estimate of the summed level of error likely in the ALBA data, as well as how such errors may affect the final results. Table: Caption: Body: <html><body><table><tr><td></td><td>Amplitude</td><td>Major Axis microns</td><td>microns</td><td>Minor Axis Position Angle degrees</td></tr><tr><td>Data Fit</td><td></td><td>59.6 ¬± 0.1</td><td>23.8 ¬± 0.5</td><td>15.9 ¬± 0.2</td></tr><tr><td>Model</td><td>357.70</td><td>60</td><td>24</td><td>16</td></tr><tr><td>1% errors</td><td>357.59¬±0.26</td><td>59.87 ¬± 0.11</td><td>23.77¬±0.22</td><td>15.83 ¬± 0.14</td></tr><tr><td>10% errors</td><td>359.79 ¬± 2.33</td><td>60.02 ¬± 1.01</td><td>27.71 ¬± 1.58</td><td>17.49 ¬± 1.61</td></tr></table></body></html> TABLE IV. Error analysis from modeling. The first row lists the measurements from Nikolic et al. (2024) We start by creating a FITS image of a Gaussian model with the shape of the ALBA electron beam, for which we adopt a dispersion of $6 0 \\mu \\mathrm { m } \\times 2 4 \\mu \\mathrm { m }$ , and major axis position angle $= + 1 6 ^ { o }$ CCW from the horizontal. This model image is converted into arcseconds using the distance between the mask and the synchrotron source (15.05 m). We also generate a configuration file corresponding to the 5-hole mask used in our experiments, with baselines and hole size scaled to get uv-coordinates in wavelengths. A uv-data measurement set is then generated from the model and the configuration using the CASA task ‚ÄôSIMOBSERVE‚Äô, resulting in a 10 visibility measurement set with the proper uv-baseline distribution, primary beam size, and model visibilities (complex coherences). | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | V. PROCESSING CHOICES The analysis presented herein is meant as supporting material for other papers that present the science results. Our main focus is to justify the choices made in this new type of analysis of laboratory optical interferometric data. A. Centering: phase slopes For reference, Figure 14 shows the centers found with and without smoothing of the input image. Centering will affect mean phases and phase slopes across apertures. We have found that smoothing before centering, ie. centering on the Airy disk not the peak pixel, leads to the minimum phase slopes across the u,v sampled points, as seen in Figure 5. The scatter plot shows similar overall scatter with and without Airy disk centering, but there is a systematic shift, which leads to phase slopes across apertures. Figure 15 shows a cut in the Y direction across the phase distribution for different centering. The phase slopes are clearly reduced with centering on the Airy disk. Closure phase could be affected by centering of the image on the CCD ‚Äì the outer parts of the Airy disk, beyond the first null are sampled differently. For reference, the counts beyond the first null without bias subtraction contribute about $4 0 \\%$ to $4 5 \\%$ to the total counts in the field with 3 mm holes and 1ms integations hole data. | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | Figure 13 shows the closure phases for all ten triads in the uv-sampling, and the values are listed in Table III. All the closure phases are stable (RMS variations $\\leq 0 . 7 ^ { o }$ ), and all the values are close to zero, typically $\\leq 1 ^ { o }$ . The only triads with closure phases of about $2 ^ { o }$ involve the baseline 0-2. This is the vertical baseline of $1 6 \\mathrm { m m }$ length, and hence has a fringe that projects (lengthwise) in the horizontal direction. The origin of closures phases that appear to be very small, but statistically different from zero, is under investigation. For the present, we conclude the closure phases are $< 2 ^ { o }$ . Closure phase is a measure of source symmetry. X-ray pin-hole measurements imply that the beam is Gaussian in shape to high accuracy (Elleaume et al. 1995). A closure phase close to zero is typically assumed to imply a source that is point-symmetric in the image plane (a closure phase $\\leq 2 ^ { o }$ implies brightness asymmetries $\\leq 1 \\%$ of the total flux, for a well resolved source), as would be the case for an elliptical Gaussian. However, the fact that the source is only marginally resolved (Section III), can also lead to small closure phases, regardless of source structure on scales much smaller than the resolution. A simple test using uv-data for a very complex source that is only marginally resolved, shows that for closed triads composed of baselines with coherences $\\ge 7 0 \\%$ , the closure phase is $< 2 ^ { o }$ . In this case, even small, but statistically non-zero, closure phases provide information on source structure. | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | To check if some of the decoherence of 3 ms vs 1 ms data could be caused by changing gain solutions in the joint fitting process, in Figure 25 we show the illumination values for the 5-holes derived from 1 ms vs. 3 ms data from the source fitting procedure. The illumination is defined as $\\mathrm { G a i n ^ { 2 } }$ , which converts the voltage gain from the fitting procedure into photon counts (ie. power vs. voltage). We then divide the 3 ms counts by 3, for a comparison to 1ms data (ie. counts/millisecond). Figure 25 shows that the derived illuminations are the same to within 2%, at worst, which would not explain the 5% to $1 0 \\%$ larger coherences for 1!ms data. In Section VII we consider the effect of averaging time on all the data, including 2-hole and 3-hole measurements. E. Bias subtraction We have calculated the off-source mean counts and rms for data using 2, 3, and 5-hole data, and for 1mÀú s to 3 ms averaging, and for 3 mm and 5 mm holes. The off-source mean ranged from 3.43 to 3.97 counts per pixel, with an rms scatter of 5 counts in all cases. We have adopted the mean value of 3.7 counts per pixel for the bias for all analyses. The bias appears to be independent of hole size, number of holes, and integration time, suggesting that the bias is | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | In radio interferometry, the voltages at each element are measured by phase coherent receivers and amplifiers, and visibilities are generated through subsequent cross correlation of these voltages using digital multipliers (Thomson, Moran, Swenson 2023; Taylor, Carilli, Perley 1999). In the case of optical aperture masking, interferometry is performed by focusing the light that passes through the mask ( $=$ the aperture plane element array), using reimaging optics (effectively putting the mask in the far-field, or Fraunhofer diffraction), and generating an interferogram on a CCD detector at the focus. The visibilities can then be generated via a Fourier transform of these interferograms or by sinusoidal fitting in the image plane. However, the measurements can be corrupted by distortions introduced by the propagation medium, or the relative illumination of the holes, or other effects in the optics, that can be described, in many instances, as a multiplicative element-based complex voltage gain factor, $G _ { a } ( \\nu )$ . Thus, the corrupted measurements are given by: $$ V _ { a b } ^ { \\prime } ( \\nu ) = G _ { a } ( \\nu ) V _ { a b } ( \\nu ) G _ { b } ^ { \\star } ( \\nu ) , | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | IX. SUMMARY AND FUTURE DIRECTIONS A. Summary We have described processing and Fourier analysis of multi-hole interferometric imaging at optical wavelengths at the ALBA synchrotron light source to derive the size and shape of the electron beam using non-redundant masks of 2, 3, and 5 holes, plus a 6-hole mask with some redundancy. The techniques employed parallel those used in astronomical interferometry, with the addition of gain amplitude self-calibration. Self-calibration is possible in the laboratory case due to the vastly higher number of photons available relative to the astronomical case. We have considered varying hole size and varying frame time. The main conclusions from this work are: ‚Ä¢ The size of the Airy disk behaves as expected for changing hole sizes. There are many photons (millions), such that the diffraction pattern is sampled beyond the first null of the Airy disk, to the edge of the CCD field. ‚Ä¢ We develop a technique of self-calibration assuming a Gaussian model to simultaneously solve for the source size and the relative illumination of the mask (the hole-based voltage gains). The gains are stable to within $1 \\%$ over 30 seconds, and relative illumination of different holes can differ by up to $3 0 \\%$ in voltage solutions. Hence, gain corrections are required to derive visibility coherences, and hence the source size. ‚Ä¢ We show visibility phases have a peak-to-peak variation over 30 seconds of $\\sim 5 0 ^ { o }$ . Further, coherences for 3 ms frame-times for the 5-hole data are systematically lower than those for $1 \\mathrm { m s }$ frame time by up to $1 0 \\%$ , and the 3 ms coherences are much noisier than $1 \\mathrm { m s }$ . We also find the phase fluctuations are correlated on two longer and similar baselines. | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | We extract the correlated power on each of the baselines by calculating the complex sum of pixels within a circular aperture of 7 pixels, centered at the calculated position of the baseline. With the padding used here 1 mm on the mask corresponds to 2.54 pixels in the Fourier transformed interferogram. An illustration of this procedure on the example frame is shown in Figure 18. We experimented with different u,v apertures (3,5,7,9 pixels), and found that 7 pixels provided the highest S/N while avoiding overlap with the neighboring u,v sample (Section V B). The interferometric phases of the visibilities are derived by a vector average over the selected apertures in the uv-plane of the images of the Real and Imaginary part of the Fourier transform, using the standard relation: phase = arctan(Im/Re). For reference, Figure 6 shows the intensity image and visibility amplitudes for a three hole mask with 3 mm holes and 1 ms integrations, Figure 7 shows the same for one of the 2-hole mask with 3 ms integrations, and Figure 8 shows the same for the 6-hole mask and 1 ms integrations. The u,v pixel locations of the Fourier components are dictated by the mask geometry (ie. the Fourier conjugate of the hole separations or ‚Äôbaselines‚Äò), and determined by the relative positions of the peaks of the sampled u,v points to the autocorrelation. These are set by the sampled baselines in the mask, the Fourier conjugate of which are the spatial frequencies. We find that the measured u,v data points are consistent with the mask machining to within $0 . 1 \\mathrm { m m } ,$ and that the u,v pixel locations for the common u,v sampled points between the 2-hole, 3-hole, and 5-hole mask agree to within 0.1 pixel. | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | $$ where, $\\star$ denotes a complex conjugation. The process of calibration determines these complex voltage gain factors. In general, calibration of interferometers can be done with one or more bright sources (‚Äòcalibrators‚Äô), whose visibilities are accurately known (Thomson, Moran, Swenson 2023). Equation (2) is then inverted to derive the complex voltage gains, $G _ { a } ( \\nu )$ (Schwab1980, Schwab1981, Readhead & Wilkinson 1978; Cornwell & Wilkinson 1981). If these gains are stable over the calibration cycle time, they can then be applied to the visibility measurements of the target source, to obtain the true source visibilities, and hence the source brightness distribution via a Fourier transform. In the case of SRI at ALBA, we have employed self-calibration assuming a Gaussian shape for the synchrotron source, the details of which are presented in the parallel paper (Nikolic et al. 2024). Our process has considered only the gain amplitudes, corresponding to the square root of the flux through an aperture (recall, power $\\propto$ voltage2), dictated by the illumination pattern across the mask. We do not consider the visibility phases. Future work will consider full phase and amplitude self-calibration to constrain more complex source geometries. Closure phase is a quantity defined early in the history of astronomical interferometry, as a measurement of the properties of the source brightness distribution that is robust to element-based phase corruptions (Jennison 1958). Closure phase is the sum of three visibility phases measured cyclically on three interferometer baseline vectors forming a closed triangle, i.e., closure phase is the argument of the bispectrum $=$ product of three complex visbilities in a closed triad of elements: | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | Figure 16 shows the center pixel locations derived using Airy disk centering for the 3-hole and 5-hole data. The X values are the same. But the Y values differ by 5 pixels. The largest departures from zero closure phase for the 5-hole data all involve baseline 0-2, which is the $1 6 \\mathrm { m m }$ vertical baseline (X direction in edf file which implies a narrow fringe in Y direction). This baseline is also in the 3-hole data, and it is the baseline with fringe length oriented horizontally, which might lead to the largest deviation in the case of a change in north-south centering of the fringe pattern on the CCD. Figure 17 shows the resulting phase image without any centering. The offset of the image center from the CCD field center leads to a complete phase wrap across the uv-apertures. This compares to Figure 5, where only small phase gradients are seen after centering. B. U,V aperture radius: 3-9pix coherence and closure phases We consider the radius of the size of the aperture in the u,v plane used to derive the amplitudes and phases of the visibilities. Figure 18 shows a cut throught the center of the amplitude distribution of the u,v image. The hatched area shows the 7-pixel radius. This radius goes down to the 6% point of the ‚Äôuv-beam‚Äô. Averaging beyond 9 pixels just adds noise, and beyond 10 pixel radius gets overlap between uv-measurements eg. 2-3 and 0-1. | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | A curious result from the source size analysis (Nikolic et al. 2024), was that the electron beam size derived with from the 5-hole mask with 3 ms averaging data resulted in a larger derived beam size than the 5-hole 1 ms data. We initially assumed this was due to temporal decoherence of the 3 ms data. However, the rotating 2-hole technique, using 3 ms averaging, resulted in the correct beam size, although with larger scatter in the time series. We explore this apparent contradiction using the 3-hole data as a third comparator. In Figure 30 we show the time series of the measured visibility amplitudes (in counts) on the 16 mm vertical baseline (0-2) for the following data: 5-hole 1 ms and 3 ms, 3-hole $1 \\mathrm { m s }$ and 3 ms, and the 2-hole 3 ms (recall, no 2-hole 1 ms data was taken). This is a busy plot, but the main points can be summarized as: ‚Ä¢ The 3-hole 1ms and 5-hole 1ms visibility amplitudes (red and blue) agree nicely, with less than a percent difference in mean value of $1 8 0 \\pm 2$ , with no dropouts and low scatter. ‚Ä¢ The 2-hole 3ms and 3-hole 3ms visibilities (green and purple) also have most points of similar amplitude as the 5-hole 1ms data, with a mean value of $\\sim 1 7 8 \\pm 8$ , but the rms scatter is larger than the 1 ms data by a factor four. This larger scatter is partially due to a few points appearing as ‚Äôdropouts‚Äô, with amplitudes up to $2 0 \\%$ lower than the rest. | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | III. EXPERIMENTAL SETUP The Xanadu optical bench setup at the ALBA synchrotron light source was the same as that used in Torino & Iriso (2016), including aperture mask location, reimaging optics to achieve far-field equivalence, narrow band filters centered at 538 nm with a bandwidth of 10 nm, and CCD camera imaging. The distance from the mask to the target source, which is used to relate angular size measurements to physical size of the electron beam, was 15.05 m. The optical extraction mirror is located 7 mm above the radiation direction (orbital plane of the electrons), at a distance of 7 m from the electron beam, implying an off-axis angle of $0 . 0 5 7 ^ { o }$ We employ multiple aperture masks. Figure 1 shows the full mask on the optical bench, with the illumination pattern from the synchrotron. The full mask had 6 holes. Aperture masks of differing number of holes were generated by simply covering various holes for a given measurement. The geometry of the 6-hole mask is shown schematically in Figure 1. The mask was machined in the ALBA machine shop to a tolerance we estimate to be better than 0.1 mm in hole position and size, based on measurements of the fringe spacings in the intensity images, and coordinates of the u,v points in the visibility plane. | augmentation | Yes | 0 |
expert | Why is a non-redundant mask preferred in Carilli’s setup? | To ensure unique fringe spacings and avoid phase ambiguity from redundant baselines. | Reasoning | Carilli_2024.pdf | Note that the target source size is $\\leq 6 0 \\mu m$ , which at a distance of $\\mathrm { 1 5 . 0 5 m }$ implies an angular size of $\\leq 0 . 8 4 \\$ . For comparison, the angular interferometric fringe spacing of our longest baseline in the mask of $2 2 . 6 \\mathrm { m m }$ at $5 4 0 ~ \\mathrm { n m }$ wavelength is 5‚Äù. This maximum baseline in the mask is dictated by the illumination pattern on the mask (Figure 1). Hence, for all of our measurements, the source is only marginally resolved, even on the longer baselines. However, the signal to noise is extremely high, with millions of photons in each measurement, thereby allowing size measurements on partially resolving baselines. We consider masks with 2, 3, 5, and 6 holes. The 2-hole experiment employs a $1 6 \\mathrm { m m }$ hole separation, and the mask is rotated by $4 5 ^ { o }$ and $9 0 ^ { o }$ sequentially to obtain two dimensional information, as per Torino & Irison (2016). The 3-hole mask experiment employs apertures Ap0, Ap1, and Ap2. The 5-hole experiment used all of the apertures except Ap5 (see Figure 2). | augmentation | Yes | 0 |
IPAC | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | BEAM TEST The final beam experiment was carried out at BNL-ATFUED beamline. The 1.7MeV photoemission beam was injected to the FC lens. Three retractable Beam Profile Monitor (BPM) screens and associated cameras are the primary diagnostic tools. The upstream beam was focused using the RF photogun solenoid. Two upstream correctors were used to align the beam going through the FC lens. The current and voltage signals to drive the FC lens were recorded in a remotely controlled oscilloscope. The trigger signal was provided from a digital delay box (DG535), which set the precise timing delay from the machine master trigger to synchronize the beam with the pulsed FC lens. It ensures each electron bunch will experience the maximum focusing strength from the FC lens. The statistic from the recorded current profile also indicates $1 0 ^ { \\wedge _ { - 4 } }$ level stability of the drive current. It should be pointed out that the $1 0 ^ { \\wedge _ { - 4 } }$ stability is mainly attributed to the Heinzinger precision voltage source that we used for the current pulse forming circuit. $1 0 \\mathord { \\uparrow } . 5$ level stability can be achieved with their a high end product line. During the experiment, images at three BPMs were recorded different FC drive currents. At each value, hundreds of images were recorded to check the strength jitter. There was no observable position jitter in BPMs after the FC lens. The $\\mathtt { B z }$ values of the FC lens are converted using the measured current and the bench measurement results prior to the beam test. Around $2 . 6 \\mathrm { k G }$ of field can make the crossover, the smallest beam size, at the distance of BPM-B ${ \\sim } 0 . 3 3 \\mathrm { m }$ from the FC center. The Zoom-in images near the crossover strength (Fig. 9) reveals the occurrence of astigmatism. The beam injection alignment (position and angle) may attribute it, which can be easily corrected with help from upstream steering coils or downstream stigmator. | augmentation | NO | 0 |
IPAC | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | Beam Position Monitors Figure 6 shows a typical example of the position measurement from a BPM against the set displacement. One BPM sits before the IP and another after; these plots are interpolations to the IP. Table 4 summarizes the agreement of the set and measured values for each scan taken. A slope of “1” corresponds to perfect agreement. Yellow showed a consistent overshoot, thus a $2 \\%$ correction was applied with a remaining $1 \\%$ uncertainty. Blue, on the other hand, showed a large store to store variation of this agreement. Thus no correction was applied and we assume a $2 \\%$ uncertainty for the beam separation measurement in the blue ring. Another way the BPMs may add to the uncertainty is by the absolute measurements of the beam position. While this absolute position does not enter the measurement of the width of the overlap area, it could mask an asymmetric offset and thus a crossing angle. Such a crossing angle would appear as a reduced collison rate. To determine the size of such an offset, the separation between yellow and blue beams was measured with the DX BPMs when they were fully overlapping. The separation at this point must be zero; however, false beam separations were measured, indicating an error. Depending on the store and the plane they vary between $- 4 0 \\mu \\mathrm { m }$ and $2 6 0 \\mu \\mathrm { m }$ and could mask a small crossing angle of at most $5 0 \\mu \\mathrm { r a d }$ . Such a small angle is negligible [4]. | augmentation | NO | 0 |
IPAC | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | File Name:BEAM-BASED_ALIGNMENT_OF_BEAM_POSITION_MONITORS.pdf BEAM-BASED ALIGNMENT OF BEAM POSITION MONITORS AT SLS 2.0 M. Böge→, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland Abstract Large initial beam position monitor (BPM) o!sets have to be reduced by one order of magnitude by means of beambased calibration (alignment) (BBA) in order to match the element-to-element magnet alignment error. At SLS 2.0 the BBA will be performed with respect to adjacent auxiliary quadrupole magnets, which are also employed for optics and tune correction. Di!erent static and dynamic techniques can be applied to determine the o!sets. The error of the individual measurements needs to be at the $\\mu \\mathrm { m }$ level to guarantee the necessary reproducibility of position and angle at the beamline source points on medium- and long-term time scales. INTRODUCTION Initial beam position monitor (BPM) o!sets with respect to the neighboring magnets are typically more than one order of magnitude larger than the element-to-element alignment of the magnet assembly. The contributions are of electronical and mechanical origin. These can be reduced by careful calibration of the electronics and surveying the BPM blocks after the installation of the vacuum system. Nevertheless the remaining o!sets can be significant. Without further correction the machine performance can be significantly degraded. Especially the feed-down from beam o!sets in sextupoles generates beta-beat and coupling and is thus detoriating the dynamic aperture. As a consequence beam assisted calibration (beam-based alignment, BBA) techniques need to be exploited. Typically the BPMs are calibrated with respect to the magnetic centers of adjacent quadrupoles or sextupoles by measuring di!erence orbit or tune changes. The quadrupole method is preferred since the precision is easily pushed to the $1 \\mu \\mathrm { m }$ level. The alignment to sextupoles is then defined by the magnet alignment tolerances. It should be noted that the high precision is needed to guarantee the medium- to long-term reproducibility of reference orbit positions for beamlines. For commissioning it is su"cient to reduce the remaining BBA o!sets to the element-to-element alignment error of $3 0 \\mu \\mathrm { m }$ . | augmentation | NO | 0 |
IPAC | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | Table: Caption: Table 1: FCC-ee Mid Term Review (MTR) Parameters [2] Body: <html><body><table><tr><td>Running mode</td><td>Z</td><td>WW</td><td>ZH</td><td>tt</td></tr><tr><td>Beam energy [GeV]</td><td>45.6</td><td>80</td><td>120</td><td>182.5</td></tr><tr><td>Bunches /beam</td><td>11200</td><td>1780</td><td>440</td><td>60</td></tr><tr><td>Hor. emit.εx [nm]</td><td>0.71</td><td>2.17</td><td>0.71</td><td>1.59</td></tr><tr><td>Vert. emit.εy [pm]</td><td>1.9</td><td>2.2</td><td>1.4</td><td>1.6</td></tr><tr><td>Hor.IP beta β*[mm] Vert. IP beta β* [mm]</td><td>110</td><td>220</td><td>240</td><td>1000</td></tr><tr><td>σz (BS)[mm]</td><td>0.7 15.5</td><td>1 5.41</td><td>1</td><td>1.6</td></tr><tr><td>Hor.BB§x [10-3]</td><td>2.2</td><td>13</td><td>4.70 10</td><td>2.17 73</td></tr><tr><td>Vert.BB §y [10-3]</td><td>97.3</td><td>128</td><td>88</td><td></td></tr><tr><td>Crab waist k [%]</td><td></td><td></td><td></td><td>134</td></tr><tr><td>Lumi. /IP</td><td>70</td><td>55</td><td>50</td><td>40</td></tr><tr><td>[1034 cm-2 s-1]</td><td>141</td><td>20</td><td>5.0</td><td>1.25</td></tr></table></body></html> INTERACTION REGION DESIGN The Interaction Region (IR) optics are based on a nanobeam, crab-waist collision scheme [4] with large Piwinski angle to allow $\\beta _ { y } ^ { * }$ to be smaller than the bunch length without significant hourglass effect. Crab sextupoles are used to rotate the $\\beta _ { y } ^ { * }$ at the IP as a function of the horizontal particle position, so that the vertical waists always align with the peak density of the opposing beam. Thereby, the crab sextupoles also suppress betatron resonances coupling the vertical and horizontal motion. Feedback Relevant Hardware Luminosity monitors (“lumicals”) are situated at $1 . 1 \\mathrm { m }$ from the IP, on either side, with a target absolute measurement precision of $1 \\times 1 0 ^ { - 4 }$ [5]. Attached to each lumical is a button Beam Position Monitor (BPM), fitted on the shared elliptical beam pipe. Further BPMs are located outside of the final focus quadrupole system and between the first and second quadrupole. A beamstrahlung (BS) dump is located $5 0 0 \\mathrm { m }$ downstream of the IP, and it is proposed to have a BS monitor along this photon line. | augmentation | NO | 0 |
IPAC | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | Over the past few years, we have focused on testing two beam size measurement setups, both based on x-ray diffraction optics. The first one is based on using Fresnel zone plates (FZP) and the second is based on diffraction using multiple crystals. FZPs allow imaging the beam in 2D, providing size and tilt information simultaneously. The first possibility of using a single zone plate to image the source in the dipole was explored and reported in [3, 4]. However, with a very small vertical beam size at the focus $( \\sim 2 - 3 ~ \\mu \\mathrm { m } )$ , it was not possible to measure correctly with a $5 \\mu \\mathrm { m }$ thick scintillator. Since there is a trade-off between scintillator thickness and yield, we focused on testing a transmission $\\mathbf { x }$ -ray microscope (TXM) using two FZPs. The magnified image allows relaxing the resolution requirements on the detector. Here, we report on the recently set up TXM for measuring the beam height at the SLS. Another technique that was explored was the multi-crystal diffraction-based $\\mathbf { \\boldsymbol { x } }$ -ray beam property analyser (XBPA). The XBPA uses a double crystal monochromator (DCM) along with a Laue crystal in dispersive geometry, to preserve the energy-angle relationship [5]. The Laue crystal is set to diffract near the centre angle of the DCM diffracted beam. Due to the dispersive geometry, the profile of the transmission beam contains a sharp valley. Its width is proportional to the beam size in a single dimension (the diffraction plane). The valley is a convolution of the valley profile of a point source and the projected spatial profile of the source on the detector, which gives a broadened valley width. The source profile can thus be obtained by deconvolution of the projected spatial profile from the measured profile. This has been meticulously reported in Ref. [5], where the vertical beam size was measured at the SLS from a bending magnet source. To measure the horizontal beam size, a horizontally deflecting DCM and Laue crystal setup is required. | augmentation | NO | 0 |
IPAC | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | Energy Calibration A principle task for the FCC-ee is ultra-precise measurement of electroweak $Z$ and $W$ ) observables, for which an accurately determined collision energy is key. This involves beam energy calibration every 10-15 minutes using noncolliding polarised pilot bunches (pilots), which circulate simultaneously with the main colliding bunches. The energy of these pilots is measured by resonant depolarisation (RDP), where the frequency of a kicker magnet is adjusted until the pilot’s polarisation vanishes. Pilot bunches are polarised in the main ring at the start of every fill using wiggler magnets, a process that takes roughly $2 \\mathrm { h }$ . Wigglers are then turned off before injection of the main colliding beam. Pilots then have a combined Touschek and gas scattering lifetime less than $2 0 \\mathrm { h }$ [8], after which the beam must be dumped to re-fill with polarised pilots. In $Z H$ and $t { \\bar { t } }$ modes, the energy spread makes RDP impossible. Measurement is instead achieved by observing collisions at the interaction point (IP). This is significantly less accurate, but removes the need for polarisation at the start of every fill. Further, with top-up injection, physics can continue theoretically indefinitely, until a beam dump occurs due to machine fault or schedule end. In these modes, pilots are used to verify optics before full energy injection. | augmentation | NO | 0 |
IPAC | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | A generator with the same properties used for the simulations was constructed, with the resulting beam propagated over $1 4 0 \\mathrm { m }$ . The measured transversal profiles are shown in Fig. 5. A clear resemblance to the simulation can be seen. The beam is optimized such that the central part of the pattern is visible on the camera, to allow the reference plane to be detected. Even though the decrease in contrast is evident at $1 4 0 \\mathrm { m }$ , it was still possible to detect the reference plane. Misalignment Detection Transversal intensity distributions of different LB patterns measured at $9 \\mathrm { m }$ and $5 2 \\mathrm { m }$ were analyzed using the centroiding algorithm, with the results shown in Fig. 6. The centroid from each row is plotted in red, with the fitted average shown in yellow. The algorithm’s performance decreases as the number of lines in the image increases. This is seen through the higher spread in centroid points along the fitted average. To test the algorithm and its ability to detect misalignment in accelerator components, the LB was propagated inside the pipe over $2 \\mathrm { m }$ to mitigate the influence of atmospheric fluctuations in refractive index on the stability of the beam. For future system it is foreseen that the beam will propagate in vacuum so that this effect can be completely neglected. For this test the camera chip was located at the end of the pipe and mounted on a motorized linear stage as illustrated in Fig. 7. The repeatability of the stage movement was in the tenths of $\\mu \\mathrm { m }$ . The chip was moved perpendicularly to the beam by a known amount, to simulate the misalignment of a component, and this misalignment was simultaneously evaluated using the beam displacement analysis. The chip stayed in one position for several seconds to further mitigate the effect of the atmospheric disturbances by taking the mean detected position from several frames. A projection lens with a focal length of $7 5 \\mathrm { m m }$ was used in this case. | augmentation | NO | 0 |
IPAC | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | All the BPMs were calibrated at the start of the run with nominal intensity bunches, by looking at the reconstruction of the beam position while the beam orbit was fixed and the jaws were moved together in ten steps of $2 0 0 \\mu \\mathrm { m }$ . The calibration showed an excellent slope of $1 . 0 0 3 \\pm 0 . 0 4 3$ , with a residual sum of squares of $0 . 0 0 2 8 \\pm 0 . 0 0 1 9$ for all BPMs. Due to positive experience with already installed BPMequipped collimators, all new collimators in the LHC now incorporate BPMs. In preparation for the High Luminosity LHC (HL-LHC) [10], which aims to increase the levelled luminosity by a factor of five compared to the nominal LHC, the collimation system underwent upgrades during the 2018- 2021 Long Shutdown, replacing four primary (TCP) and eight secondary (TCS) collimators in the betatron cleaning ALIGNMENT Aligning the collimator jaws to the beam is a crucial step for attaining a good cleaning performance. In BLMbased alignments, both jaws are moved towards the beam in small steps until a loss spike is detected on the downstream BLM [5]. This indicates that one of the jaws has scraped a small part of the beam. Next, the two jaws are moved inwards one-by-one and stopped at the location where another loss spike is detected. The jaws are now centered around the beam and can be retracted to their nominal gap. If there is an angle of the jaws with respect to the beam, the alignment result can be adversely a"ected. To find this angle, one can apply a large tilt to the collimator jaws and align the upstream and downstream corners individually. Further details on BLM-based angular alignments, including more complex methods, are described in [14, 15]. | augmentation | NO | 0 |
Expert | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | D. Coupling dependence of the measured beam profiles The coupling dependences were measured by changing the currents of the skew-quadrupole coils wound on two kinds of sextupole magnets. Figure 20 shows the typical beam profiles when a skew correction was carefully carried out [Fig. 20(a)] and all of the skew-quadrupole coils were turned off on purpose [Fig. 20(b)]. As shown in Fig. 20, we found that the vertical beam size increased and the measured beam profile was tilted when a skew correction was not applied. In order to measure the coupling dependence precisely, we measured the two sets of beam profiles at the same beam current when a skew correction was applied (hereafter called ‘‘skew on’’ condition), and the skewquadrupole coils were turned off (called ‘‘skew off’’ condition). Figure 21 shows all of the results of the two conditions of skew on and skew off. As shown in Fig. 21, the vertical beam sizes increased for all of the stored currents under the skew off condition compared with those under the skew on condition, while the horizontal one decreased. In order to estimate the coupling ratio, we also plot the calculation data including intrabeam scattering effect in Figs. 21(a) and 21(b). The data set of the skew on (skew off) condition agree with the calculation assuming the $0 . 5 \\%$ $( 3 . 0 \\% )$ coupling ratio. The absolute values of the measured tilt angles of the skew off condition are $( 6 \\pm$ 2) degrees, which is much larger than that of skew on condition of $( 0 . 7 \\pm 0 . 3 ) \\$ degrees. | 5 | NO | 1 |
IPAC | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | The Q-scan curve obtained for the y-direction is shown in Fig. 3. Where $\\sqrt { | K | }$ is a value proportional to the focusing force of the quadrupole magnet. Fitting using Eq. (3) results in an emittance $8 \\%$ lower than the simulation input. This is because the beam in the y-direction is shaved o! about $1 \\%$ by the beam pipe, resulting in an underestimation of emittance. The Q-scan curve obtained for the $\\mathbf { \\boldsymbol { x } }$ and $\\textbf { Z }$ -direction is shown in Fig. 4. By varying the focusing force of both the quadrupole magnet and the buncher, the Q-scan curve is fitted with a bivariate function as in Eq. (4). Where f $\\mathrm { ( E _ { 0 } L T ) }$ is a value proportional to the focusing force of the buncher. The results of the fitting showed that the diagnostic error of emittance was within $1 \\%$ . 1 司 。 。。 O 1 0° oQoo 。 C 。 。 。 [9 8000o。8Q0000 。 C0 Q00000 。 C-0.2 r .3 <元 T 0.5 980000000.6 10.0.8 8 9 VK[/m]6 Requirements for Beam Monitor The requirement of emittance error is less than $10 \\%$ for the acceleration test [9]. On the other hand, the above evaluation results do not include the resolution of the BPM. The expected measured beam width $( \\sigma _ { \\mathrm { e x p . } } )$ ) can be expressed using the expected actual beam width $( \\sigma _ { \\mathrm { s i m . } } )$ and the monitor resolution $( \\sigma _ { \\mathrm { B P M } } )$ by the following relation, | 4 | NO | 1 |
IPAC | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | ALIGNMENT TOLERANCES & BBA Two optics were developed, named the Global Hybrid Correction (GHC) and Local Chromatic Correction (LCC) optics, respectively. Table 2 presents the rms misalignments of arc quadrupoles and sextupoles leading to $1 \\%$ rms beta beating or $1 \\mathrm { m m }$ rms spurious vertical dispersion, for the $Z$ mode. The results show that LCC holds the promise of more relaxed tolerances for the arc. For the interaction region the differences are less pronounced and sensitivities tighter [16]. Work on the LCC dynamic aperture is still in progress, especially for the higher beam energies. The initial mechanical pre-alignment shall be improved by beam-based alignment (BBA). For a machine as large as the FCC-ee, parallel BBA (PBBA) is desired, where the centers of multiple quadrupoles or sextupoles are determined at the same time. Two PBBA methods for quadrupoles were explored in simulations [17, 18]. Considering $1 \\mu \\mathrm { m }$ BPM noise, residual systematic errors of the PBBA are of order $1 0 { - } 3 0 \\mu \\mathrm { m }$ [18]. One source of systematic error is the orbit angle at the rather long quadrupoles. Table: Caption: Table 2: Magnet Misalignments Leading to $1 \\%$ rms Beta Beating or $1 \\mathrm { m m }$ rms Dispersion Body: <html><body><table><tr><td>Optics</td><td>△βx/βx</td><td>△βy/βy</td><td>Dy</td></tr><tr><td>GHC quadr.</td><td>2.9 μm</td><td>0.7 μm</td><td>0.1 μm</td></tr><tr><td>LCC quadr.</td><td>6.1 μm</td><td>0.5 μm</td><td>0.26 μm</td></tr><tr><td>GHC sext.</td><td>17 um</td><td>8.5 μm</td><td>2.6 μm</td></tr><tr><td>LCC sext.</td><td>>100 μm</td><td>46 um</td><td>10 um</td></tr></table></body></html> | 4 | NO | 1 |
Expert | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | This paper is organized as follows. In the next section, we briefly present the principle of the FZP monitor. In Sec. III, we show the experimental setup of the FZP monitor, especially the improvements. Some measurement results by using the improved FZP monitor are shown in Sec. IV. The last section is devoted to conclusions. II. PRINCIPLE OF FZP MONITOR In this section, we briefly summarize the theoretical aspects of the FZP monitor and its resolution. (See Ref. [14] for details.) A. X-ray imaging optics The principle of a beam-profile measurement is as follows. The FZP monitor is based on the $\\mathbf { \\boldsymbol { x } }$ -ray imaging optics with two FZPs, a condenser zone plate (CZP), and a microzone plate (MZP). It has the structure of a longdistance microscope, as shown in Fig. 1. When the electron beam emits $\\mathbf { \\boldsymbol { x } }$ -ray SR light, the transverse electron-beam image is magnified on the focal plane by using this optics. The magnification, $M$ , of the imaging optics is determined by $M = M _ { \\mathrm { C Z P } } \\times M _ { \\mathrm { M Z P } }$ , where $M _ { \\mathrm { C Z P } }$ and $M _ { \\mathrm { M Z P } }$ are the magnifications of CZP and MZP. $M _ { \\mathrm { C Z P } }$ and $M _ { \\mathrm { M Z P } }$ are basically defined as $M _ { \\mathrm { C Z P } } = L _ { \\mathrm { C 2 } } / L _ { \\mathrm { C 1 } }$ , where $L _ { C 1 }$ is the length from the SR source point to the CZP and $L _ { C 2 }$ is from the CZP to the intermediate focal point; $M _ { \\mathrm { C Z P } } =$ $L _ { M 2 } / L _ { M 1 }$ , where $L _ { M 1 }$ is the length from the intermediate focal point to the MZP and $L _ { M 2 }$ is from the MZP to a final focal point on an $\\mathbf { X }$ -ray CCD, as shown in Fig. 1. The imaging optics should be designed and optimized so that the required spatial resolution and magnification are obtained. | 2 | NO | 0 |
Expert | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | As the shutter opening time becomes shortened, the background component becomes larger than the peak signal of the obtained beam image. In order to measure the beam profiles precisely and analyze them in detail, we carefully subtracted this background component from the data of $\\mathbf { X }$ -ray CCD, as follows. The transverse position of the beam image is much more sensitive, by a factor of 200 of the magnification of MZP, than a transverse change of the MZP. Thanks to the newly installed x-ray pinhole mask, the area of the transmitted x ray, which is one of the background, is drastically reduced. Therefore, by changing the transverse position of the MZP by only a few microns vertically, the beam image does not overlap the transmitted x ray. The alignment error of this position change of the MZP is too small to deform the obtained beam image on the x-ray CCD by the effect of aberrations. After changing the position of the MZP, the background of $\\mathbf { X }$ -ray CCD is subtracted. These procedures for background subtraction allow us to measure the beam profiles easily and precisely. Figure 10 shows a measured beam image after background subtraction. The shutter opening time was fixed with $1 ~ \\mathrm { m s }$ . A clear beam image was observed on the $\\mathbf { \\boldsymbol { x } }$ -ray CCD camera. This beam image, as shown in Fig. 10, was obtained by superposing 10 different beam images with the same current and same trigger timing from beam injection after background subtraction in order to gain the signal-tonoise ratio. The horizontal and vertical beam profiles were obtained by projecting the beam image to each direction. In | 4 | NO | 1 |
Expert | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | E. X-ray pinhole mask The background on the CCD image mainly consists of the readout noise of the $\\mathbf { X }$ -ray CCD circuit and the $\\mathbf { \\boldsymbol { x } }$ -ray beam transmitted through the FZPs, which is not focused at all. The transmitted x rays through the MZP appear on the x-ray CCD as a square of about $3 \\ \\mathrm { m m } \\times 3 \\ \\mathrm { m m }$ , reflecting its MZP structure. Because the transmitted $\\mathbf { X }$ ray depended on the beam current, we needed to prepare background data of each beam current in the old setup to subtract the background component. In order to reduce the background component of the transmitted $\\mathbf { X }$ ray, an $\\mathbf { X }$ -ray mask system with a pinhole was installed near the fast mechanical shutter. The $\\mathbf { \\boldsymbol { x } }$ -ray mask was made of stainless steel and can be moved in the horizontal and vertical directions. Figure 9 shows the CCD images before and after insertion of the $\\mathbf { \\boldsymbol { x } }$ -ray mask with the pinhole diameter of $3 0 0 \\ \\mu \\mathrm { m }$ . The size of the background area was greatly reduced by using this $\\mathbf { X }$ -ray mask. | 4 | NO | 1 |
Expert | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | DOI: 10.1103/PhysRevSTAB.10.042801 PACS numbers: 07.85.Qe, 07.85.Tt, 41.75.Ht, 41.85.Ew I. INTRODUCTION A. Introduction to the FZP monitor The production of low-emittance beams is one of the key techniques for electron accelerators and synchrotron light sources. For example, a third-generation synchrotron light source and future synchrotron light sources, like an energy recovery linac (ERL), require an unnormalized emittance of a few nm rad or less (hereafter we redefine the word of ‘‘emittance’’ as ‘‘unnormalized emittance’’). In highenergy physics, the linear collider also requires such ultralow emittance beams to realize the necessary luminosity. The Accelerator Test Facility (ATF) was built at High Energy Accelerator Research Organization (KEK) in order to develop the key techniques of ultralow emittance beam generation and manipulation. The ATF consists of a $1 . 2 8 \\ \\mathrm { G e V }$ S-band electron linac, a damping ring, and an extraction line [1]. A low-emittance beam is generated in the ATF damping ring, where the horizontal emittance at a zero current is $1 . 1 \\times 1 0 ^ { - 9 }$ m rad. The target value of the vertical emittance at a zero current is $1 . 1 \\times 1 0 ^ { - 1 1 }$ m rad, which has been generated by applying precise vertical dispersion corrections and betatron-coupling corrections [2]. The typical beam sizes are less than $5 0 \\ \\mu \\mathrm { m }$ horizontally and less than $1 0 \\ \\mu \\mathrm { m }$ vertically. Such small beam sizes cannot be measured by the typically used visible-light imaging optics for synchrotron radiation (SR) because of the large diffraction limit of visible light. Beam-profile monitoring with good spatial resolution is crucially important to confirm whether the required extremely small emittance beam is stably generated and manipulated. Therefore, there are some special monitors set and developed in the ATF: tungsten and carbon wire scanners in the extraction line, a double-slit SR interferometer, a laser wire monitor, and a Fresnel zone plate monitor. | augmentation | NO | 0 |
Expert | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | We briefly summarize the history of measurements of emittance in the ATF damping ring. First, the horizontal emittance was successfully measured by the tungsten and/ or carbon wire scanner set on the extraction line [3], and was also measured by a double-slit SR interferometer. However, the vertical emittance was not clearly measured with these monitors. In the case of the wire scanner, the spurious dispersion and coupling from the large horizontal emittance could be easily mixed with the vertical direction [4]. On the other hand, a vertical beam-size measurement by a double-slit SR interferometer, which used the spatial pattern of the interference of the visible SR passed through a double slit with an fixed interval [5], had an uncertainty because the measured vertical beam size in the ATF damping ring was almost at its resolution limit [6]. To avoid these uncertainties, a laser wire monitor was developed to measure directly the vertical beam size in the ATF damping ring [7]. This monitor is based on the Compton scattering of electrons with a thin laser light target, called a laser wire. By scanning the laser wire instead of the solid tungsten and carbon wire, quasinondestructive measurements can be performed in the ATF damping ring, and the vertical emittance was successfully measured [8–10]. Unfortunately, we could measure the beam size only in one direction. Therefore, we did not know the $x$ -y coupling of the transverse beam profile. When there is a $x { - } y$ coupling in the transverse beam motion, the measured vertical beam size is contaminated by the horizontal one and the beam profile will become tilted by rotating toward the original two transverse directions perpendicular to the electron-beam motion. The vertical beam size cannot be measured precisely as long as the tilt of the beam profile caused by the $x \\cdot$ -y coupling is unknown. Furthermore, it takes several minutes to finish the measurement of the one directional beam size by the laser wire monitor. Thus, the effects of the beam drift and/or the mechanical vibration, which excites the beam motion of the same order as vertical beam size, cannot be removed off during the vertical beam-size measurement by the laser wire monitor. For precise beam-profile monitoring, it is necessary to know the beam image, which has much information about not only the horizontal and vertical beam sizes, but also the beam positions, beam current, tilt of the beam profile caused by the $x { - } y$ coupling, and its distribution, by direct monitoring of the beam image in a short time. This situation led us to develop a new beam-profile monitor based on $\\mathbf { \\boldsymbol { x } }$ -ray imaging optics by using Fresnel zone plates (FZPs). | augmentation | NO | 0 |
Expert | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | Beam emittance in the ATF damping ring is dominated by the intrabeam scattering effect [2]. In a high current of the single-bunch mode, the emittance increases as the beam current become high, and the coupling ratio decreases. In order to estimate the coupling ratio of the ATF damping ring and validate these measured beam sizes, we compared the measured beam sizes with calculation obtained by using the optics data of the ATF damping ring in Table IV and the computer program SAD [21] including the intrabeam scattering effect [22,23]. Figure 16 shows comparisons of the measured beam size (boxes) and the calculation (lines) on $2 0 0 5 / 4 / 8$ . Figure 17 also shows the data of the measured data (boxes and circles) and calculation (lines) on $2 0 0 5 / 6 / 1$ . The horizontal axes show the beam current of the damping ring in the single-bunch mode, and the vertical axes are the measured and calculated beam sizes. These two measurements agree well with the calculation when it is assumed that the coupling ratio is $( 0 . 5 \\pm 0 . 1 ) \\%$ and are almost consistent with the other measurement by the laser wire monitor in the ATF damping ring, described in Ref. [2]. In order to confirm the assumption of coupling ratio, the energy spread was also measured. Figure 18 shows the measured energy spread at the extraction line on $2 0 0 5 / 4 / 8$ . The errors of the measured momentum spread at higher beam current are mainly caused by the measurement error of the dispersion function at the screen monitor. On the other hand, the errors of the momentum spread at lower beam current are mainly caused by the statistical error because of the poor signal of the screen monitor. As shown in Fig. 18, the measured energy spread at the extraction line on $2 0 0 5 / 4 / 8$ also agrees well with a calculation under the assumption of a $( 0 . 5 \\pm 0 . 1 ) \\%$ coupling ratio. | augmentation | NO | 0 |
Expert | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | $$ where the $\\lambda$ is the wavelength of a photon and $f$ is the focal length for the wavelength. The spatial resolution $\\delta$ which is the transverse size of a point-source image for the 1st-order diffraction on the focal plane, is determined by $$ \\delta = 1 . 2 2 \\Delta r _ { N } , $$ where $\\Delta r _ { N }$ is the width of the outermost zone and the suffix $N$ means the total number of zones. If $N \\gg 1$ , it can be expressed as $$ \\Delta r _ { N } = f \\lambda / 2 r _ { N } = \\frac { 1 } { 2 } \\sqrt { \\frac { \\lambda f } { N } } . $$ The spatial resolution $\\delta$ of FZP corresponds to the distance between the center and the first-zero position of the Airy diffraction pattern. When we apply a Gaussian distribution with the standard deviation $\\sigma$ to its Airy diffraction pattern, the spatial resolution $\\delta$ almost equals the $3 \\sigma$ distance $( \\delta \\simeq 3 \\sigma )$ . C. Expected spatial resolution of the FZP monitor In order to measure a small beam profile, the spatial resolution of the FZP monitor must be smaller than the beam size. The total spatial resolution of the FZP monitor is determined by three mechanisms. One is the diffraction limit of $\\mathbf { \\boldsymbol { x } }$ -ray SR light. Another is the Airy diffraction pattern of FZP, as described in Eqs. (2) and (3). The other is the pixel-size of the $\\mathbf { \\boldsymbol { x } }$ -ray CCD camera, itself. We summarize the spatial resolution determined by each parameter in Table I. | augmentation | NO | 0 |
Expert | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | The diffraction limit is determined by the wavelength of x-ray SR $\\lambda = 0 . 3 8 3 ~ \\mathrm { { n m } }$ , which corresponds to $3 . 2 4 \\mathrm { k e V } \\mathrm { x } .$ - ray energy, and the divergence angle $\\sigma _ { { \\mathrm { S R } } }$ of $1 2 6 \\ \\mu \\mathrm { r a d }$ , which is obtained from the bending field of the ATF damping ring. Airy diffraction patterns of the FZPs also determine the limit of the measurable beam size. The image of the point source focused by each FZP has a finite width of the Airy diffraction pattern $\\delta$ as shown in Sec. II B. The spatial resolution, determined by CZP (MZP), is $\\sigma _ { \\mathrm { C Z P } } / \\bar { M } _ { \\mathrm { C Z P } }$ ${ \\bf \\omega } _ { \\mathrm { \\left( \\sigma _ { M Z P } / \\it M \\right) } }$ . The outermost zone widths, $\\Delta r _ { N }$ , of CZP and MZP are listed in Table II. These $\\Delta r _ { N }$ ’s were limited by the fabrication technology, and the outermost zone width could not be reduced by less than $1 0 0 \\mathrm { n m }$ [16]. However, we note that the effect of the Airy pattern on the spatial resolution is also less than $1 \\ \\mu \\mathrm { m }$ . Finally, we need to consider the pixel size of the $\\mathbf { \\boldsymbol { x } }$ -ray CCD camera. When one CCD pixel is $\\Delta x \\times \\Delta x$ square, its resolution, $\\sigma _ { \\mathrm { C C D } }$ , is $\\Delta x / 2 \\sqrt { 3 }$ in rms. Then, the measurable beam size is determined by $\\sigma _ { \\mathrm { C C D } } / M$ . In our monitor, one pixel is $2 4 \\mu \\mathrm { m } \\times$ $2 4 \\ \\mu \\mathrm { m }$ square, as shown in Table III. The spatial resolution determined by the CCD pixel size $( \\sigma _ { \\mathrm { C C D } } / M )$ is $0 . 3 5 \\ \\mu \\mathrm { m }$ in rms. The total spatial resolution is estimated from the sum of squares of these resolutions. The expected total spatial resolution of this monitor results in about $0 . 7 \\ \\mu \\mathrm { m }$ in rms. Submicron spatial resolution is expected for this FZP monitor. | augmentation | NO | 0 |
Expert | Why is beam-based alignment critical for the FZP monitor? | It prevents optical aberrations that distort beam profile measurements. | Reasoning | Sakai_2007.pdf | The beam-profile monitor with x-ray imaging optics will allow precise and direct beam imaging in a nondestructive manner because the effect of the diffraction limit can be neglected by using x-ray SR. Some beam-profile monitors based on the x-ray imaging optics were performed by using FZP and a refractive $\\mathbf { \\boldsymbol { x } }$ -ray lens [11,12]. However, they used a knife-edge scanning technique to measure the beam profile because the beam image was reduced by using only one FZP or a single refractive $\\mathbf { \\boldsymbol { x } }$ -ray lens. Therefore, it took a long time to measure a beam profile. In order to overcome this defect, we proposed a real-time beam-profile monitor based on magnified $\\mathbf { \\boldsymbol { x } }$ -ray imaging optics using ‘‘two’’ FZPs (hereafter called as ‘‘FZP monitor’’) [13]. We originally developed the FZP monitor in the ATF damping ring to measure a small beam profile. For this purpose, the spatial resolution of this monitor was designed to be less than $1 \\ \\mu \\mathrm { m }$ . With this FZP monitor, we succeeded to obtain a clear electron-beam image enlarged by 20 times with two FZPs on an x-ray CCD, and measuring an extremely small electron-beam size of less than $1 0 \\ \\mu \\mathrm { { m } }$ [14]. Recently, a beam-profile monitor using a single FZP and an $\\mathbf { X }$ -ray zooming tube has been developed at the SPring-8 storage ring [15]. In this monitor, the magnified beam image was also obtained by using an $\\mathbf { X }$ -ray zooming tube, where x rays were converted to photoelectrons before magnification. It has a small spatial resolution of $4 \\mu \\mathrm m$ . With this monitor at the SPring-8 storage ring, $\\mathbf { X }$ -ray images of the electron beam were clearly obtained, and the vertical beam size with $1 4 \\ \\mu \\mathrm { m }$ in root mean square (rms) was successfully measured with a 1 ms time duration. | augmentation | NO | 0 |
IPAC | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | associated with varying delays in the digitization paths for different groups of channels. INTRODUCTION Ionization Profile Monitors (IPMs) have been developed at Brookhaven National Laboratory (BNL) to measure transverse beam profiles in RHIC [1–3]. When the beam passes through the beamline, it ionizes the background gas and emits electrons. Those electrons are swept transversely from the beamline and collected by the Multi-Channel Plates (MCP) on 64 strip anodes oriented parallel to the beam axis. An IPM collects and measures the distribution of those electrons1. Ideally, the distributions should be independent of where the beam signal locates in the IPM. In other words, if the beam is moved across the channels, the IPM measurements from different locations should have identical shapes. One iteration of such channel scanning by moving beams across different channels is called a position scan. The gain value of each channel is the dominant factor in determining what a final distribution looks like. There are various errors existing in the system that can affect the channel gains. Figure 1 illustrates the beam profiles from a position scan without calibration. We can see that the beam profile has a large variation when measured from different locations. The channel gain errors may result from initial channel-to-channel gain variations, depletion of channel gains due to aging, etc. There are also systematic errors | augmentation | NO | 0 |
IPAC | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | The dependence of the axially symmetrical beam density on the radius is measured by averaging one arch of beam imaged discussed above. The centre of the distribution is reconstructed from the shape of the arch. An example of the beam arch picture at $1 4 0 0 { \\mathrm { ~ e V } }$ is presented on Fig. 5 (left). The scalloping becomes apparent on the profile pictures, one of which is shown on Fig. 5 (right). The profile is compared with 2-D TRACK simulations [6]. Although the beam resembles the predicted distribution, the dimensions are larger in approximately 2-3 times due to the insufficient magnetic field. Beam Current The Faraday cup is almost the same size as the Ce:YAG screen and is oriented perpendicular to the path of the electrons. However, since the beam from the hollow source diverges, only a fraction of the total beam current is incident on the Faraday cup. The response of the measurement network to the rising edge of the current pulse seen by the Faraday cup includes a resonant ringing along with an exponentially decay when the electron current is constant. Both the height of the peak of the response and the total integrated value of the detected pulse are proportional to the current, with a calibration factor provided by the manufacturer. | augmentation | NO | 0 |
IPAC | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | INTRODUCTION With the increasing demand for hadron beam therapy, there is a parallel rise in the demand for online, non-invasive beam diagnostics. However, most of the commercially available diagnostics are either fully invasive to the beam or if less invasive, can still effect the properties during the measurements. This necessitates conducting diagnostic measurements while beam is not indenting on the patients during quality assurance (QA) tests. This can raise concerns about the hadron beam therapy as any malfunction on the accelerator end can alter the beam properties at any time and potentially leading to incorrect dosage delivery or delivery at a different location. A continuous beam monitoring system could overcome these issues by proving constant feedback to the accelerator system. The QUASAR group at the Cockcroft Institute is currently working on the development of a supersonic gas jet based in-vivo dosimeter which can be directly integrated with treatment facilities. This dosimeter uses a supersonic gas jet shaped into a screen to detect the beam using ionization profile monitor. The underlying principle of ionization profile monitors (IPMs) involves detecting the ionization products (ions or electrons) resulting from the Coulomb interaction between primary beam particles and residual gas molecules. This detection is facilitated by a strong external electrostatic field applied perpendicular to the beam’s direction of propagation. IPMs are considered to be as either non-invasive or minimally invasive beam profile monitors, capable of real-time operation, making them highly desirable for particle accelerator. To capture both transverse profiles of the primary beam [1], it is recommended to use two IPMs oriented at right angles to each other, however both cannot occupy the same location. In ultra-high vacuum accelerators, these devices are constrained by both acquisition speed as well as resolution due to significant signal reduction. | augmentation | NO | 0 |
IPAC | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | A laserwire diagnostic is under development for installation on the Front End Test Stand (FETS) at the Rutherford Appleton Laboratory (RAL) [5]. FETS consists of 5 sections; an ion source, a low energy beam transport (LEBT), a radiofrequency quadrupole (RFQ), a medium beam energy transport (MEBT), and a laserwire diagnostic system prior to a dipole and beam dump. The instrument will be capable of measuring transverse emittance and both transverse, and longitudinal beam profile measurements. The longitudinal profiling is achieved by reducing the laser pulse duration to be less than the ion beam temporal spread and sampling several synchronisation times between the laser and ion bunch. The transverse measurements are made by scanning the laserwires transverse offset in relation to the ion beam with a vertically, or horizontally, aligned laserwire. A detector capable of measuring the resulting signal from the laser-ion interaction is under development. One potential configuration would be to use a scintillator screen with a CCD to detect the resulting photons from the ${ \\mathrm { \\bf H } } ^ { 0 }$ incident on the screen. DETECTOR CONFIGURATION A potential detector system could consist of a scintillator to absorb the ${ \\mathrm { \\bf H } } ^ { 0 }$ and emit optical photons, to be detected by a CCD. By orienting the scintillator at $4 5 ^ { \\circ }$ angle relative to the ${ \\mathrm { \\bf H } } ^ { 0 }$ incident axis, the surface of the scintillator could be imaged by a CCD placed parallel to the ${ \\mathrm { H } } ^ { 0 }$ axis. A lens can be used to focus the image of the scintillator plane onto the CCD. When placing the lens the angle between the lens plane and the image place must be calculated adhering to the Scheimpflug principle. The Scheimpflug principle describes the geometry relating the plane of focus to the image plane, and subsequently the lens plane. An illustration of the setup for the scintillator, lens, and image plane is shown in Fig. 2. The angle between the plane of focus (in this case the scintillator surface), and the image plane, is given as $\\psi$ and the angle between the lens plane and the image plane is $\\theta$ . The two angles are related as | augmentation | NO | 0 |
IPAC | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | At the entrance of the beam delivery pipe, a motorized platform is present, which hosts the beam entrance diagnostics. These include a Faraday Collector to measure beam intensity and an optical system to display the beam spot on a fluorescent ceramic. In order to reduce the scattering of the beam, the propagation in the delivery pipe occurs in helium (He) atmosphere. The delivery pipe is $1 . 7 \\mathrm { m }$ long, and is composed of two cylindrical pipes joined together. The first, $5 1 \\mathrm { m m }$ in diameter and $7 0 0 \\mathrm { m m }$ long, can be inserted in the magnet poles and the second, $1 9 8 \\mathrm { m m }$ in diameter and $1 \\mathrm { m }$ long, carries the beam close to the experimental area. The diameter of this second pipe has been chosen to allow the deflected beam passing through without colliding with pipe walls. The pipe is sealed from the external atmosphere using Kapton (polyimide) windows. The beam at the exit of the delivery pipe propagates through $6 0 ~ \\mathrm { c m }$ in air up to the target plane that is placed at $2 . 7 \\mathrm { m }$ from SCDTL-8 exit. A commercial monitor (FlashQ model, produced by De.tec.tor.) developed for proton therapy is installed at the exit of the delivery pipe and will be used to qualify and verify the beam scanning process. It consists of four ionization chambers (two integral and two stripped plates) with an active area of $1 3 \\ \\mathrm { c m } \\ x \\ 1 3 \\ \\mathrm { c m }$ and is mounted on a motorized platform, allowing it to be moved from the delivery line output window up to the target plane. A beam shutter, consisting of a Faraday Collector that can measure deflected beam intensity, is located after the ionization chamber. | augmentation | NO | 0 |
IPAC | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | Beam Position Monitors Figure 6 shows a typical example of the position measurement from a BPM against the set displacement. One BPM sits before the IP and another after; these plots are interpolations to the IP. Table 4 summarizes the agreement of the set and measured values for each scan taken. A slope of “1” corresponds to perfect agreement. Yellow showed a consistent overshoot, thus a $2 \\%$ correction was applied with a remaining $1 \\%$ uncertainty. Blue, on the other hand, showed a large store to store variation of this agreement. Thus no correction was applied and we assume a $2 \\%$ uncertainty for the beam separation measurement in the blue ring. Another way the BPMs may add to the uncertainty is by the absolute measurements of the beam position. While this absolute position does not enter the measurement of the width of the overlap area, it could mask an asymmetric offset and thus a crossing angle. Such a crossing angle would appear as a reduced collison rate. To determine the size of such an offset, the separation between yellow and blue beams was measured with the DX BPMs when they were fully overlapping. The separation at this point must be zero; however, false beam separations were measured, indicating an error. Depending on the store and the plane they vary between $- 4 0 \\mu \\mathrm { m }$ and $2 6 0 \\mu \\mathrm { m }$ and could mask a small crossing angle of at most $5 0 \\mu \\mathrm { r a d }$ . Such a small angle is negligible [4]. | augmentation | NO | 0 |
IPAC | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | Table: Caption: Table 1: Transport Matrix Elements Body: <html><body><table><tr><td colspan="4">SlitstoFODOStart</td></tr><tr><td></td><td>Sim.</td><td>Meas.</td><td>|△|</td></tr><tr><td>M11</td><td>-0.359</td><td>-0.388 ± 0.000</td><td>0.03</td></tr><tr><td>M12</td><td>0.161</td><td>-0.262 ±0.002</td><td>0.42</td></tr><tr><td>M33</td><td>-0.724</td><td>-0.761 ± 0.001</td><td>0.04</td></tr><tr><td>M34</td><td>-0.859</td><td>-0.937 ± 0.002</td><td>0.08</td></tr></table></body></html> Table: Caption: Body: <html><body><table><tr><td colspan="4">SlitstoFODOMiddle</td></tr><tr><td></td><td>Sim.</td><td>Meas.</td><td>|△|</td></tr><tr><td>M11</td><td>-0.155</td><td>-0.240 ± 0.001</td><td>0.08</td></tr><tr><td>M12</td><td>-0.697</td><td>-0.855 ± 0.003</td><td>0.16</td></tr><tr><td>M33</td><td>0.051</td><td>-0.131 ± 0.009</td><td>0.18</td></tr><tr><td>M34</td><td>-0.320</td><td>-0.434 ± 0.017</td><td>0.12</td></tr></table></body></html> Table: Caption: Body: <html><body><table><tr><td colspan="4">SlitstoFODOEnd</td></tr><tr><td></td><td>Sim.</td><td>Meas.</td><td>|△|</td></tr><tr><td>M11</td><td>0.171</td><td>-0.002 ±0.002</td><td>0.17</td></tr><tr><td>M12</td><td>-0.998</td><td>-0.955 ± 0.006</td><td>0.03</td></tr><tr><td>M33</td><td>0.774</td><td>0.649 ±0.002</td><td>0.12</td></tr><tr><td>M34</td><td>0.473</td><td>0.390 ±0.003</td><td>0.08</td></tr></table></body></html> In order to measure the full beam profile with the collimating slits, many images are recorded while scanning the slits across the phase space footprint. To get enough of the beam shape to measure beam profile at the screens the slits must be scanned around the full size of the beam. This results in images that contain no beam on the screen, all images above a signal threshold of $1 { - } 2 \\%$ (dependent on noise of camera used) are summed to create a composite image. A profile is created from this composite image then the Wiener smoothing function is used and the profile is thresholded at $5 \\%$ of max intensity as shown in Fig. 2. From this profile rms is calculated (Table 2). Table: Caption: Table 2: Beam rms Values at Screens Body: <html><body><table><tr><td colspan="4">FODOLine X-RMS</td></tr><tr><td></td><td>Sim. (mm)</td><td>Meas. (mm)</td><td>% Diff.</td></tr><tr><td>Start</td><td>1.403</td><td>1.380</td><td>1.67</td></tr><tr><td>Middle</td><td>1.134</td><td>1.425</td><td>20.42</td></tr><tr><td>End</td><td>0.816</td><td>0.900</td><td>9.33</td></tr></table></body></html> Table: Caption: Body: <html><body><table><tr><td colspan="4">FODOLine Y-RMS</td></tr><tr><td></td><td>Sim. (mm)</td><td>Meas. (mm)</td><td>% Diff.</td></tr><tr><td>Start</td><td>1.205</td><td>1.220</td><td>1.23</td></tr><tr><td>Middle</td><td>0.846</td><td>0.476</td><td>77.72</td></tr><tr><td>End</td><td>1.797</td><td>1.434</td><td>25.31</td></tr></table></body></html> The resulting profiles and rms are then compared to simulated results created using PyORBIT [7] and an input bunch created from measured data. To create the bunch, three 2D measurements are done in $( x , x ^ { \\prime } ) , ( y , y ^ { \\prime } )$ , and $( \\phi , \\mathrm { d E } )$ , then interpolated to form the full bunch. This bunch is used for all simulations in this paper. To compare to the measured profiles at screens the simulation is ran without the space charge solver, and bunch statistics are calculated in a similar manner. At each screen location a histogram is created from the output bunch, which is wiener smoothed and thresholded at $5 \\%$ of max intensity. All profiles are normalized by area (Fig. 2). | augmentation | NO | 0 |
IPAC | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | $$ \\mathcal { T } _ { j } = \\frac { \\mathrm { v } } { c S } j + \\mathcal { T } _ { 0 } $$ $$ I _ { j } = C _ { t o t } \\frac { \\sum _ { i } \\mathcal { P } _ { i j } } { \\sum _ { i j } \\mathcal { P } _ { i j } } \\frac { c S } { \\mathrm { ~ v ~ } } $$ The pair $\\{ \\mathcal { T } _ { j } , I _ { j } \\}$ represents the beam current profile projected onto the $j ^ { t h }$ row CCD pixel. It’s important to note that we assume all beam charges are projected onto the YAG screen. Thus, we can map the two-dimensional YAG image $\\mathcal { P }$ into the beam current profile $\\{ \\mathcal { T } , I \\}$ using Eqs. (2) and (3). Twiss Parameters Profile $c$ are the machine parameters that only depend on the FODO lattice structure. Notice that this is different from the thin lens approximation. | augmentation | NO | 0 |
IPAC | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | The measurement was performed by focusing the beam on the first FC using the Tandem injector ion optics [4]. Then measuring the profiles in the plane of the first FC and in the plane of the second FC in steps of $1 \\mathrm { m m }$ in $y$ direction. Obtained beam profiles as a function of Faraday cup position $y _ { F C }$ are displayed in Fig. 3. The vertical profiles were fitted with Gaussian distributions, to obtain $( \\bar { y } , \\sigma _ { y } )$ : ‚Ä¢ Peak position $\\bar { y } _ { F C _ { 1 } } = 1 . 0 \\ : \\mathrm { m m }$ , $\\bar { y } _ { F C _ { 2 } } = 3 . 1 \\mathrm { m m }$ , ‚Ä¢ Beam width: $\\sigma _ { F C _ { 1 } } = 3 . 5 \\ : \\mathrm { m m }$ , $\\sigma _ { F C _ { 2 } } = 6 . 0 \\ : \\mathrm { m m }$ . Thus obtaining the beam shift: $\\Delta \\bar { y } = \\bar { y } _ { F C _ { 2 } } - \\bar { y } _ { F C _ { 1 } } =$ $1 . 7 \\mathrm { m m }$ and beam width shift $\\Delta \\sigma = \\sigma _ { F C _ { 2 } } - \\sigma _ { F C _ { 1 } } = 2 . 5 \\mathrm { m m }$ per meter of ion flight. Here it needs to be empahsized that $\\sigma _ { F C _ { 1 } } , \\sigma _ { F C _ { 2 } }$ are not the property of the actual beam distribution $f ( x , y )$ , but beam current distribution ${ \\cal I } ( y _ { \\mathrm { F C } } )$ : | 4 | NO | 1 |
IPAC | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | This also leads to having unusable data points when individual pre-amplifiers for a channel fail giving disconnected data points within a profile. During data analysis, the channels that were marked to be inoperative were set to the average value of the overall IPM data set to eliminate the poor MCP issue. Out of all 64,000 turns, both horizontal and vertical IPMs store the data locally but only return the first 1000 turns for analysis. This allows to calculate the sigma $\\sigma$ that represents the beam size. The IPMs were used to study the change in beam size in the MI by changing the MCP voltage to determine its e!ects as both were functioning compared to the vertical IPM not working in the RR. The R-square of the fits were also calculated to analyze the quality of the fits and this determined which voltage range was the best fit. Once an ideal MCP voltage range was determined, the beam size and the emittance were analyzed by using intensity as the dependent. Afterwards, the emittance of the beam was calculated by using $\\sigma$ in Eq. (1) where $\\beta$ is a Twiss parameter, $D$ is dispersion, and $\\frac { \\delta p } { p _ { 0 } }$ is the momentum spread. | 2 | NO | 0 |
Expert | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | V. CONCLUSION In this paper, we have presented an improvement of the FZP monitor and measurement results of the ultralow emittance beam in the ATF damping ring under various conditions. First, by thermally disconnecting the Si crystal from the stepping motor, the position drift of the obtained image was drastically reduced by a factor of 100, and fully stabilized within a few $\\mu \\mathrm { m }$ for one day. Second, we modified the FZP folder for a more precise beam-based alignment using $\\mathbf { \\boldsymbol { x } }$ -ray SR. This avoids the effects of aberrations due to any misalignments of the FZPs. Third, the newly installed fast mechanical shutter allowed us to measure a beam image within $1 \\mathrm { m s }$ . In addition, the $\\mathbf { \\boldsymbol { x } }$ -ray CCD was synchronized with the beam-injection timing. We could measure the beam profile under the fully damped condition in the normal operation mode. At last, installation of the $\\mathbf { \\boldsymbol { x } }$ -ray pinhole mask system greatly reduced the background of x rays passing through the MZP. With the improved system, beam-profile measurements were performed on three days. By using a fast mechanical shutter, we could remove the effect of an unknown $1 0 0 \\mathrm { H z }$ oscillation, which enlarged the measured vertical beam size, for the beam-profile measurement. We therefore could perform precise beam-profile measurements with a 1 ms shutter opening time. After carefully applying the skew correction, the measured horizontal beam sizes were about $5 0 \\ \\mu \\mathrm { m }$ , and the vertical beam sizes were about 6 $\\mu \\mathrm { m }$ at above $3 \\ \\mathrm { m A }$ stored current in the single-bunch mode, which corresponded to about $1 1 \\ \\mathrm { p m }$ rad of the vertical emittance. The measured beam sizes were in a good agreement with a calculation assuming coupling ratios of $( 0 . 5 \\pm$ $0 . 1 ) \\%$ . In addition, the measured energy spread also agreed well with the calculation. Thanks to the improved x-ray CCD and shorter time resolution of the newly installed fast mechanical shutter, we could also precisely measure the damping time of the ATF damping ring when the damping wigglers were turned on and off. The measurement results of the vertical damping ring agreed well with the design values. Furthermore, the coupling dependence of the beam profiles was obtained. Not only the horizontal and vertical beam sizes, but also the beam tilt angles, were measured precisely under the two coupling conditions. From these measurements, good performance of the improved monitor was confirmed. | 5 | NO | 1 |
Expert | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | From these measurements, we conclude that the beamsize enhancement, especially vertically, is caused by the $1 0 0 ~ \\mathrm { H z }$ oscillation; the FZP monitor, itself, is working well, and electron beam might be oscillated with $1 0 0 ~ \\mathrm { H z }$ frequency. 3. Data analysis and results For data analysis, fitting with a two-dimensional Gauss function was applied to the beam images. We set 7 free parameters with horizontal and vertical centers, horizontal and vertical widths, peak height, the tilt angle, and the offset. The positive direction of tilt angle was counterclockwise to the electron-beam motion. The fitting results of the horizontal beam size $\\sigma _ { x }$ , vertical beam size $\\sigma _ { y }$ , and tilt angle $\\theta _ { b }$ are summarized in Table V for three different days after the skew correction. The two sets of data (named as ‚Äò‚Äò1st‚Äô‚Äô and ‚Äò‚Äò2nd‚Äô‚Äô) were taken on $2 0 0 5 / 6 / 1$ . The 1st data were taken after first making a skew correction. To confirm the reproducibility, skew magnets were turned off once, and turned on again; 2nd data on $2 0 0 5 / 6 / 1$ were taken under this condition. The shutter opening time was fixed at | 5 | NO | 1 |
Expert | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | B. Si monochromator The Si crystal monochromator can be rotated horizontally by using a goniometer and vertically by using a stepping motor, which is attached to the support of a Si crystal in a vacuum. With the old monochromator, the vertical position of the beam image on the CCD camera had largely drifted because the support of the Si crystal was deformed by heat from the stepping motor. In order to avoid any drift, a new Si crystal monochromator was produced. Figure 3 shows a picture of the new monochromator. In the new monochromator, a stepping motor was thermally isolated from the Si crystal by ceramic insulators and thermally stabilized by copper lines connected with a water-cooled copper plate. Figure 4 shows measurements of the beam centroid by the old and new monochromator, respectively. After this improvement, the drift was drastically reduced by a factor of about 100 and stabilized within a few $\\mu \\mathrm { m }$ for a long time, as shown in Fig. 4. C. Fresnel zone plate The new FZP folders were designed and fabricated so that the FZPs could be controlled and removed from the optical path in the vacuum if necessary. The removed FZPs are protected from the air pressure during any leaks in maintenance and repair of the monitor beam line, or the installation of new beam line components. The FZPs have never been damaged by air pressure during vacuum work since the new FZP folders were installed. Furthermore, the new folders allowed us to establish a more precise beambased alignment scheme by using only the $\\mathbf { \\boldsymbol { x } }$ -ray CCD camera. A precise alignment of the FZP monitor component is crucial to avoid degradation of the spatial resolution due to aberration. The alignment procedure was greatly improved with respect to the old setup: first the center position of the $\\mathbf { \\boldsymbol { x } }$ -ray beam reflected by the Si crystal (corresponding to the position of the optical axis) is measured with the x-ray CCD without FZP imaging. After that, the CZP is inserted to the optical path and the CZP position is adjusted to the optical axis. After inserting the CZP on the optical path, a clear image of the CZP can be detected by illumination of the raw $\\mathbf { X }$ -ray SR light, and hence the center position of the CZP can be obtained. Figure 5 shows an image of a raw $\\mathbf { X }$ -ray SR detected by the x-ray CCD and an image of the CZP on the $\\mathbf { X }$ -ray CCD after inserting the CZP. The MZP position is also adjusted in the same manner. The minimum alignment error can be one pixel of the CCD $( 2 4 \\ \\mu \\mathrm { m } )$ for the CZP and $1 / 2 0 0$ (the reciprocal of the MZP magnification $M _ { \\mathrm { M Z P , } }$ ) of one pixel for the MZP. The FZP tilt angle to the optical path is decided mainly by the machining accuracy and estimated to be less than $0 . 5 ^ { \\circ }$ . We note that the effect of these aberrations of the FZP monitor is calculated by not only ray-tracing analysis, but also the wave optics [17,18]. | 4 | NO | 1 |
Expert | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | FIG. 10. (Color) Typical beam image obtained by the FZP monitor after the background was subtracted. Beam current was a $4 . 4 \\mathrm { \\ m A }$ in a single-bunch mode. The shutter opening time was fixed to $1 \\ \\mathrm { m s }$ . The horizontal and vertical bars of $5 0 ~ \\mu \\mathrm { m }$ show the scales at the source point. order to determine the horizontal and vertical beam sizes, we fitted each beam profile to a Gaussian curve with four parameters of its center, width, peak height, and offset. The horizontal and vertical beam profiles and their fitted Gaussian curves are shown in Fig. 11. The horizontal axes in Fig. 11 show the beam positions, which were converted to the scale at the source point by dividing the magnification factor $M = 2 0$ . The measured horizontal and vertical beam sizes were about $5 0 \\ \\mu \\mathrm { m }$ and about $6 \\mu \\mathrm { m }$ for three measurements. 2. Shutter opening time dependence of the measured beam size The measured beam size can be increased by mechanical vibrations and/or jitter coming from electrical noises. In order to study these effects, we measured the dependence of the beam sizes on the shutter opening time prior to a precise beam-profile measurement. Figure 12 shows the measured horizontal and vertical beam sizes as a function of the shutter opening time. The beam current was fixed to $4 \\mathrm { \\ m A }$ during these measurements. The error bar was mainly due to the fitting error assuming a Gaussian, as described in Sec. IV B 1. We found that the measured horizontal beam size was almost $5 0 \\ \\mu \\mathrm { m }$ , and was independent of the shutter opening time. On the other hand, the vertical beam size was changed from 9 to $7 \\ \\mu \\mathrm { m }$ by shortening the shutter opening time from 4 to $1 ~ \\mathrm { m s }$ or less. In order to investigate this enhancement, we measured the image center of the CCD as a function of the trigger time of the fast mechanical shutter from beam injection with a fixed opening time. Figure 13 shows the dependences of the measured horizontal and vertical beam image centers as a function of the shutter trigger time with $1 ~ \\mathrm { m s }$ shutter opening time. All of the data were obtained in the radiation equilibrium of the ATF damping ring. We found the horizontal and vertical oscillations of the beam position. Both oscillations were well fitted to a sinusoidal curve with $1 0 0 ~ \\mathrm { H z }$ frequency. We note that the position oscillation was also found at $4 0 0 ~ \\mathrm { { m s } }$ after beam injection with the same amplitude and the same phase of $1 0 0 \\mathrm { H z }$ frequency. Furthermore, when we measured the beam profiles 10 times with the same shutter trigger timing, this oscillation was reproduced within these error bars. These results mean that the image center was clearly oscillating with the $1 0 0 \\mathrm { H z }$ frequency in the synchronization with the injection timing. To translate the image center oscillation to the beam oscillation, with amplitude $A _ { b }$ , the sinusoidal function was magnified with the magnification factor $M = 2 0$ of the FZP monitor. These beam oscillation amplitudes were found to be $A _ { b } = 1 4 . 9 \\pm 1 . 6 \\mu \\mathrm { m }$ horizontally and $A _ { b } = 7 . 8 4 \\pm 0 . 4 5 \\mu \\mathrm { m }$ vertically. The vertical beam oscillation significantly affects the beam size because the vertical oscillation is of the same order as the vertical beam size. From these measurements, we concluded that the vertical $1 0 0 ~ \\mathrm { H z }$ oscillation caused a vertical beam-size enhancement. | augmentation | NO | 0 |
Expert | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | Beam emittance in the ATF damping ring is dominated by the intrabeam scattering effect [2]. In a high current of the single-bunch mode, the emittance increases as the beam current become high, and the coupling ratio decreases. In order to estimate the coupling ratio of the ATF damping ring and validate these measured beam sizes, we compared the measured beam sizes with calculation obtained by using the optics data of the ATF damping ring in Table IV and the computer program SAD [21] including the intrabeam scattering effect [22,23]. Figure 16 shows comparisons of the measured beam size (boxes) and the calculation (lines) on $2 0 0 5 / 4 / 8$ . Figure 17 also shows the data of the measured data (boxes and circles) and calculation (lines) on $2 0 0 5 / 6 / 1$ . The horizontal axes show the beam current of the damping ring in the single-bunch mode, and the vertical axes are the measured and calculated beam sizes. These two measurements agree well with the calculation when it is assumed that the coupling ratio is $( 0 . 5 \\pm 0 . 1 ) \\%$ and are almost consistent with the other measurement by the laser wire monitor in the ATF damping ring, described in Ref. [2]. In order to confirm the assumption of coupling ratio, the energy spread was also measured. Figure 18 shows the measured energy spread at the extraction line on $2 0 0 5 / 4 / 8$ . The errors of the measured momentum spread at higher beam current are mainly caused by the measurement error of the dispersion function at the screen monitor. On the other hand, the errors of the momentum spread at lower beam current are mainly caused by the statistical error because of the poor signal of the screen monitor. As shown in Fig. 18, the measured energy spread at the extraction line on $2 0 0 5 / 4 / 8$ also agrees well with a calculation under the assumption of a $( 0 . 5 \\pm 0 . 1 ) \\%$ coupling ratio. | augmentation | NO | 0 |
Expert | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | IV. MEASUREMENT OF THE ULTRALOW EMITTANCE BEAM IN THE ATF DAMPING RING A. Beam tuning and condition We obtained a data set of the beam profile mainly for three days with various damping-ring conditions after improving the FZP monitor. In all cases the ATF ring was operated at $1 . 2 8 \\mathrm { G e V }$ in single-bunch mode. Typical stored beam current in the ATF damping ring is above $3 . 5 ~ \\mathrm { m A }$ , which corresponds to $1 . 0 \\times 1 0 ^ { \\hat { 1 0 } }$ electrons per bunch, during beam-profile measurements. Before the measurement, the electron beam in the ATF damping ring was tuned as follows. First, the closed-orbit distortion and verticalmomentum dispersion were reduced as much as possible. Second, the coupling between the horizontal and vertical betatron oscillations was minimized by optimizing two sets of skew magnets wound around two series of sextupole magnets, respectively. This process, called ‘‘skew correction,’’ is a key to production of a low-emittance beam [19]. In 2005, a study of the effect by damping wigglers set on the two straight sections in the ATF damping ring was started [20]. We also studied the effect of the damping wigglers on the damping time by using the improved FZP monitor. The measurement dates and beam conditions are listed below. | augmentation | NO | 0 |
Expert | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | Table: Caption: TABLE I. Expected spatial resolution of each parameter and the total expected spatial resolution. Body: <html><body><table><tr><td>Parameters</td><td>Definition</td><td>Resolution (1σ)[μm]</td></tr><tr><td>Diffraction limit (λ= 0.383 nm)</td><td>λ/4TTOSR</td><td>0.24</td></tr><tr><td>Airy pattern of CZP (△rn = 116 nm)</td><td>0czp/MczP</td><td>0.55</td></tr><tr><td>Airy pattern of MZP (△rn = 128 nm)</td><td>OMZP/M</td><td>0.002</td></tr><tr><td>CCD(1 pixel= 24 μm × 24 μm）</td><td>σcCD/M</td><td>0.35</td></tr><tr><td>Total</td><td></td><td>0.7</td></tr></table></body></html> Table: Caption: TABLE II. Specifications of the two FZPs. Body: <html><body><table><tr><td>Fresnel zone plate</td><td>CZP</td><td>MZP</td></tr><tr><td>Total number of zone</td><td>6444</td><td>146</td></tr><tr><td>Radius</td><td>1.5 mm</td><td>37.3 μm</td></tr><tr><td>Outermost zone width △rn</td><td>116 nm</td><td>128 nm</td></tr><tr><td>Focallength at 3.24 keV</td><td>0.91 m</td><td>24.9 mm</td></tr><tr><td>Magnification</td><td>Mczp = 1/10</td><td>MmZp = 200</td></tr></table></body></html> Table: Caption: TABLE III. Specifications of the x-ray CCD camera. Body: <html><body><table><tr><td colspan="2">X-ray CCD camera</td></tr><tr><td>Type</td><td>Direct incident type</td></tr><tr><td>CCD</td><td>Back-thinned illuminated type</td></tr><tr><td>Data transfer</td><td>Full-frame transfer type</td></tr><tr><td>Quantum efficiency at 3.24 keV</td><td>>90%</td></tr><tr><td>Pixel size</td><td>24 μm X 24 μm</td></tr><tr><td>Number of pixels</td><td>512 × 512</td></tr></table></body></html> III. IMPROVEMENTS ON THE EXPERIMENTAL SETUP In this section, we present the setup of FZP monitor while concentrating on the improvements of the present setup compared to the former setup referred to as ‘‘old setup’’ in the following. A. Experimental layout Figure 2 shows the setup of the FZP monitor. SR light is extracted at the bending magnet (BM1R.27) just before the south straight section in the $1 . 2 8 \\mathrm { G e V }$ ATF damping ring, where the horizontal beam size is expected to be about $5 0 \\ \\mu \\mathrm { m }$ and the vertical beam size is expected to be less than $1 0 \\ \\mu \\mathrm { m }$ . This system consists of a Si crystal monochromator, two FZPs (CZP and MZP), and an $\\mathbf { X }$ -ray CCD camera. The specifications of the two FZPs are summarized in Table II. A beryllium window with $5 0 \\ \\mu \\mathrm { m }$ thickness is installed to isolate the relatively low vacuum of the monitor beam line from that of the ATF damping ring. $3 . 2 4 \\mathrm { k e V }$ x-ray SR light is selected by the Si(220) crystal monochromator with a Bragg angle, $\\theta _ { B }$ , of $8 6 . 3 5 ^ { \\circ }$ . The CZP and MZP are mounted on folders set on movable stages in order to align these two optical components precisely across the beam direction. Furthermore, the MZP folder can move in the longitudinal direction of the beam line to search the focal point of the MZP. The monochromatized $\\mathbf { \\boldsymbol { x } }$ -ray SR is precisely focused on the xray CCD camera by adjusting the positions of the two FZP (CZP and MZP) folders. The magnifications of the FZPs, $M _ { \\mathrm { C Z P } }$ , and $M _ { \\mathrm { M Z P } }$ , are $1 / 1 0$ and 200, respectively. Therefore, an image of the electron beam at the bending magnet is magnified with a factor of 20 on the $\\mathbf { X }$ -ray CCD camera. The specifications of the $\\mathbf { \\boldsymbol { x } }$ -ray CCD camera (C4880-21, HAMAMATSU) are summarized in Table III. The data taking timing of the $\\mathbf { X }$ -ray CCD camera is synchronized with the beam-injection timing in order to detect a beam image during the beam operation, in which the electron beam stayed within only $5 0 0 ~ \\mathrm { { m s } }$ associated with $1 . 5 6 \\ \\mathrm { H z }$ repetition of a beam injection in the ATF damping ring. A mechanical shutter is installed in front of the $\\mathbf { \\boldsymbol { x } }$ -ray CCD camera to avoid irradiating x-ray SR on the $\\mathbf { \\boldsymbol { x } }$ -ray CCD camera during data transfer. The minimum shutter opening time of this shutter is $2 0 \\mathrm { m s }$ . A new fast mechanical shutter is set between the CZP and the MZP to improve the time resolution of the FZP monitor. A detailed description of the performance is given in Sec. III D. | augmentation | NO | 0 |
Expert | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | D. Fast mechanical shutter 1. Layout The time resolution of this monitor is determined by the minimum shutter opening time of the mechanical shutter. We newly install a fast mechanical shutter in the $\\mathbf { X }$ -ray beam line in order to improve the time resolution to less than $2 0 ~ \\mathrm { { m s } }$ . Figure 6 shows a block diagram of the FZP monitor after installation. The minimum opening time of the mechanical shutter is determined by the aperture. Therefore, we applied a fast mechanical shutter with a $1 ~ \\mathrm { m m }$ diameter aperture (UHS1ZM2, VINCENT), which is a factor 5 smaller than the shutter located, in the old setup, in front of the $\\mathbf { \\boldsymbol { x } }$ -ray CCD camera. This shutter was installed $1 0 0 ~ \\mathrm { { m m } }$ upstream of the intermediate focal point of the $\\mathbf { \\boldsymbol { x } }$ -ray imaging optics between two FZPs so as not to scrape off the image of the transverse beam profile. The fast mechanical shutter was housed in a vacuum chamber and can be moved across the beam line by movable stages attached to this vacuum chamber. In addition, this shutter can be removed out from the optical path by the air cylinder if necessary. | augmentation | NO | 0 |
Expert | Why is it important to measure the tilt of the beam profile in the FZP monitor? | Because x–y coupling can distort the vertical size measurement if beam tilt isn’t accounted for. | Reasoning | Sakai_2007.pdf | $$ where the $\\lambda$ is the wavelength of a photon and $f$ is the focal length for the wavelength. The spatial resolution $\\delta$ which is the transverse size of a point-source image for the 1st-order diffraction on the focal plane, is determined by $$ \\delta = 1 . 2 2 \\Delta r _ { N } , $$ where $\\Delta r _ { N }$ is the width of the outermost zone and the suffix $N$ means the total number of zones. If $N \\gg 1$ , it can be expressed as $$ \\Delta r _ { N } = f \\lambda / 2 r _ { N } = \\frac { 1 } { 2 } \\sqrt { \\frac { \\lambda f } { N } } . $$ The spatial resolution $\\delta$ of FZP corresponds to the distance between the center and the first-zero position of the Airy diffraction pattern. When we apply a Gaussian distribution with the standard deviation $\\sigma$ to its Airy diffraction pattern, the spatial resolution $\\delta$ almost equals the $3 \\sigma$ distance $( \\delta \\simeq 3 \\sigma )$ . C. Expected spatial resolution of the FZP monitor In order to measure a small beam profile, the spatial resolution of the FZP monitor must be smaller than the beam size. The total spatial resolution of the FZP monitor is determined by three mechanisms. One is the diffraction limit of $\\mathbf { \\boldsymbol { x } }$ -ray SR light. Another is the Airy diffraction pattern of FZP, as described in Eqs. (2) and (3). The other is the pixel-size of the $\\mathbf { \\boldsymbol { x } }$ -ray CCD camera, itself. We summarize the spatial resolution determined by each parameter in Table I. | augmentation | NO | 0 |
IPAC | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | INTRODUCTION Particle accelerators are among the grandest machines of the twentieth century because of their contributions to medicine, materials development, renewable energy, and the many fields of high-energy physics and life sciences, with roughly a third of all Nobel Prizes in physics being related to the use or advancements of particle accelerators. However, conventional accelerators are costly due to the size required to accelerate electrons to high energy. Dielectric breakdown in the RF cavities of conventional linear accelerators limits the accelerating gradient to $E _ { z } < 5 0 \\mathrm { M e V / m }$ [1]. Circular accelerators also face major drawbacks for accelerating electrons, since energy loss due to synchrotron radiation scales with the relativistic factor to the fourth power $( \\gamma _ { b } ^ { 4 } )$ . Both limitations are overcome by increasing the size of the machine to reach higher energies. Plasma wakefield acceleration (PWFA) possesses much higher accelerating gradients with some experiments demonstrating $E _ { z } > 1 0 0 \\mathrm { G e V } / \\mathrm { m } \\ [ 2$ , 3]. This suggests that PWFA can decrease the size of accelerators from the kilometer scale to the meter scale. | augmentation | NO | 0 |
IPAC | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | INTRODUCTION In recent years charged particle acceleration using solidstate nanostructured plasmas has attracted attention as a novel method of achieving ultra-high acceleration gradients, beam manipulation and gamma- or $\\mathrm { \\Delta X }$ -ray generation $[ 1 -$ 10]. In this context, PIC simulations have shown that the excitation of carbon nanotube (CNT) or graphene based multi-channel structures using either a driver beam [1,6] or a laser pulse [2,9] might achieve electric wakefield amplitudes in the order of $\\mathrm { T V / m }$ or beyond. In this paper, we specifically investigate laser wakefield acceleration (LWFA) in multi-hollow nanostructured high density plasmas. In this setup, a single, short, high-intensity pulse drives the wakefield. To excite a wakefield, the laser pulse length $L$ must be in the order of the plasma wavelength $\\lambda _ { p }$ (see for example [11]): $L \\simeq \\lambda _ { p } = 2 \\pi / \\omega _ { p } =$ $2 \\pi \\sqrt { m _ { e } \\varepsilon _ { 0 } / ( n _ { e } e ^ { 2 } ) }$ , where $\\omega _ { p }$ is the angular frequency of the plasma, $\\scriptstyle { \\varepsilon _ { 0 } }$ the vacuum permittivity, $e$ the elementary electric charge, $m _ { e }$ the electron rest mass and $n _ { e }$ the plasma density. This ensures that the excitations created by the ponderomotive force are in phase with the pulse group velocity. | augmentation | NO | 0 |
IPAC | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | Starting from the idea proposed by Tajima and Dawson [1], who first suggested accelerating electrons produced by the interaction of a laser with a plasma, there have been many advances in laser wakefield acceleration (LWFA) over the years. These advances are largely due to significant progress in laser technology, which has made it possible to achieve ultrashort pulses (femtoseconds). Today, LWFA is not only used as a compact acceleration technique but also as a photon source [2, 3]. The radiation emitted, known as betatron radiation, is sometimes referred to as synchrotron-like [4] and has been extensively studied over the years. In the coming years, it is proposed to become a valid alternative to wellestablished light sources, as X-ray sources based on plasma accelerators promise to become compact, economically accessible sources. Their advantage lies in the shortness of the pulses produced, which fall within the femtosecond range, opening up possibilities for ultrafast photon science, along with applications in medicine, biology, and industry. BETATRON RADIATION Betatron radiation results from the oscillations of electrons within the ion bubble in plasma acceleration, such as Fig. 1. A high-intensity femtosecond laser is fired into a gas jet or gas cell below critical density. The laser’s ponderomotive force causes the removal of electrons from a region known as the bubble region or blowout regime. This regime is achieved when the waist $w _ { 0 }$ of the focused laser pulse matches the plasma $( k _ { p } w _ { 0 } = 2 \\sqrt { a _ { 0 } } )$ , with $k _ { p } = \\omega _ { p } / c$ and the pulse duration approximately half a plasma wavelength $( c \\tau \\approx \\lambda _ { p } / 2 )$ . Additionally, the laser intensity must be sufficiently high $( a _ { 0 } > 2 )$ to expel most of the electrons from the focal spot [5]. | augmentation | NO | 0 |
IPAC | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | INTRODUCTION To perform physics precision studies or discover physics beyond the Standard Model, high-energy colliders such as the existing Large Hadron Collider (LHC), the past Large Electron-Positron (LEP) or the Future Circular Collider (FCC) [1, 2] are desireable. However, limitations such as speed or radio-frequency characteristics create barriers to achieving higher physics goals, with gradient limits typically in the order of $1 0 0 { \\mathrm { M V / m } }$ due to surface breakdown, arcing, cavity damage, or wakefield effects [3, 4]. In the ’80s-’90s, Tajima and Dawson proposed laser wakefield acceleration (LWFA) where laser pulses were used as wakefield drivers [5]. To further overcome the limits of the existing techniques and achieve acceleration gradients on the order of $\\mathrm { T V / m }$ and beyond, alternative methods based on solid-state plasma wakefield were also proposed [6, 7] Taking into account that solid-state structures can have a density of conduction electrons 4-5 orders of magnitude higher compared to gaseous plasma medium [8], preionised solid-state targets might offer a way to create inhomogeneous structured plasmas, able to sustain ultra-high acceleration gradients [9, 10]. CNT array-based nanostructures can create a structured non-homogeneous plasma with a density modulation wavelength of several $\\mu \\mathrm { m }$ which can be tailored to optimize the acceleration gradient and the confinement of particles [11]. | augmentation | NO | 0 |
IPAC | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | File Name:ION-ION_COLLISIONS_IN_PLASMA_WAKEFIELD_ACCELERATORS.pdf ION-ION COLLISIONS IN PLASMA WAKEFIELD ACCELERATORS M.Yadav‚àó, K. Letko, J.B. Rosenzweig University of California, Los Angeles, California, USA Abstract The plasma wakefield accelerator, with acceleration gradients ranging from $\\mathrm { G e V / m }$ to $\\mathrm { T e V } / \\mathrm { m }$ , holds promise for propelling particles to high energies in linear colliders. This results in exceptionally bright beams characterized by intense ion-derived focusing, leading to the collapse of plasma ions. Our study extends prior research focused on electron acceleration by investigating ion-ion collisions, studying different collision models and emphasizing the near-equilibrium state post-ion collapse using the OSIRIS Particle -in-cell (PIC) code. Notably, our findings reveal that parametric excitations arising from plasma non-uniformity have an insignificant impact on phase space diffusion, a crucial insight for optimizing linear colliders. INTRODUCTION Plasma wakefield acceleration (PWFA) employs waves in a plasma medium chosen to naturally avoid breakdown issues. These waves are excited by an intense drive beam to accelerate a trailing beam. PWFAs have already demonstrated acceleration gradients exceeding $5 0 \\mathrm { G e V / m }$ . To explore the suitability of the PWFA for linear collider applications, proposals [1, 2] have been put forward that analyze the use of an afterburner at the end of a conventional linear collider injector, with the goal of doubling the beam energy [3]. | augmentation | NO | 0 |
IPAC | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | File Name:DESIGN_AND_MODELING_OF_DIELECTRIC_A_WAKEFIELD.pdf DESIGN AND MODELING OF DIELECTRIC A WAKEFIELD ACCELERATOR WITH PLASMA IONIZED WITNESS BUNCH N.M. Cook,∗ RadiaSoft LLC, Boulder, CO, USA G. Andonian, K. Kaneta, A. Pronikov, RadiaBeam Technologies, Santa Monica CA, USA Abstract A planned experiment at the Argonne Wakefield Accelerator (AWA) facility will demonstrate the plasma photocathode concept, wherein precise laser-based ionization of neutral gas within the wakefield driven by a relativistic particle beam generates a high brightness witness beam, which is accelerated in the wakefield. Replacing the plasma wakefield acceleration component with a dielectric wakefield acceleration scheme can simplify experimental realization by relaxing requirements on synchronization and alignment at the expense of accelerating gradient. However, this places rigorous constraints on drive beam dynamics, specifically charge, size, and relative separation. This paper presents progress on the design of such a hybrid scheme, including improved simulations accounting for anticipated beam properties and revised structure characteristics. INTRODUCTION Many applications can benefit from compact sources of ultrahigh brightness MeV-scale electron beams. The plasma photocathode technique, as demonstrated by the so-called “Trojan-Horse” scheme, leverages the low emittance of an RF photocathode with the accelerating and focusing properties of a plasma accelerator [1]. However, such a scheme requires sophistication, leveraging a two-component gas to act as the witness beam source and plasma waveguide, and necessitating fs-scale synchronization between an ionization pulse and the accelerating bucket, which is of the orders of hundreds of microns [2]. The use of dielectric structures to provide the accelerating response eliminates the need for multiple gas species, easing restrictions on chamber design and target optimization. Furthermore, the ten-fold larger wavelengths accessible by dielectrics significantly reduce spatiotemporal demands on the beam-laser synchronization and diagnostics. Figure 1 depicts the basic concept [3]. | augmentation | NO | 0 |
IPAC | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | File Name:SiPM_INTEGRATION_TESTING_FOR_FACET-II_PAIR_SPECTROMETER.pdf SiPM INTEGRATION TESTING FOR FACET-II PAIR SPECTROMETER J. Phillips∗, B. Naranjo, M. Yadav, J. B. Rosenzweig University of California, Los Angeles, CA, USA Abstract A pair spectrometer, designed to capture single-shot gamma spectra over a range extending from $1 0 \\mathrm { M e V }$ through $1 0 \\mathrm { G e V }$ , is being developed at UCLA for installation at SLAC’s FACET-II facility. Gammas are converted to electrons and positions via pair production in a beryllium target and are then subsequently magnetically analyzed. These charged particles are then recorded in an array of quartz Cherenkov cells attached to silicon photomultipliers (SiPMs). As the background environment is challenging, both in terms of ionizing radiation and electromagnetic pulse radiation, extensive beamline testing is warranted. To this end, we present Geant4 Monte Carlo studies, assembly of the SiPMs, and future plans of testing. INTRODUCTION Plasma wakefield acceleration (PWFA) is an acceleration technique that can provide a high-gradient field. PWFA involves sending ultra-relativistic charged particle beams, oftentimes electrons, through stationary plasma, which can be ionized either from a laser or by the fields from the beam itself [1]. Two bunches are usually sent through the plasma— a witness beam and a driver beam—though a single bunch could also be sent. The properties of plasma are useful for mitigating breakdown at high energies. In the blowout regime, the bunch density is larger than the plasma density, and the driver beam repels the electrons in the plasma surrounding it. The electrons then return from behind the beam, creating a bubble-like structure called a plasma wake. The wake creates a high-gradient, longitudinal field that accelerates the witness beam. This method of acceleration has been found to be very successful, allowing for smaller and cheaper accelerators that can still maintain high-energy acceleration. | augmentation | NO | 0 |
IPAC | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | File Name:CHARACTERIZATION_OF_METER-SCALE_BESSEL_BEAMS_FOR.pdf CHARACTERIZATION OF METER-SCALE BESSEL BEAMS FOR PLASMA FORMATION IN A PLASMA WAKEFIELD ACCELERATOR T. Nichols ‚àó, R. Holtzapple, California Polytechnic State University, San Luis Obispo, CA, USA R. Ariniello, S. Gessner, SLAC National Accelerator Laboratory, Menlo Park, CA, USA V. Lee, M. Litos, University of Colorado Boulder, Boulder, CO, USA Abstract A large challenge with Plasma Wakefield Acceleration lies in creating a plasma with a profile and length that properly match the electron beam. Using a laser-ionized plasma source provides control in creating an appropriate plasma density ramp. Additionally, using a laser-ionized plasma allows for an accelerator to run at a higher repetition rate. At the Facility for Advanced Accelerator Experimental Tests, at SLAC National Accelerator Laboratory, we ionize hydrogen gas with a $2 2 5 \\mathrm { m J }$ , 50 fs, $8 0 0 \\mathrm { n m }$ laser pulse that passes through an axicon lens, imparting a conical phase on the pulse that produces a focal spot with an intensity distribution described radially by a Bessel function. This paper overviews the diagnostic tests used to characterize and optimize the focal spot along the meter-long focus. In particular, we observe how wavefront aberrations in the laser pulse impact the peak intensity of the focal spot. Furthermore, we discuss the impact of nonlinear effects caused by a $6 \\mathrm { m m }$ , $\\mathrm { C a F } _ { 2 }$ vacuum window in the laser beam line. | 2 | NO | 0 |
IPAC | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | The Livingston plot, shown in Figure 1, illustrates how the progress in achieving the energy frontier has been enabled by the history of invention in accelerator science and technology. One can clearly see that over several decades, there has been an exponential growth in the maximum attained energy. But the exponential growth in maximum achieved energy was made possible by the development of different accelerator technologies (for example Electrostatics, Cyclotrons, Linacs, Synchrotrons, Colliders). As often occurs in any technological field, new accelerating technologies often replaced each other once the previous technology had reached its full potential and saturates its evolution curve [1]. In more recent decades, represented by the LHC collider, the exponential energy growth has started slowing down again. This suggests that existing acceleration technologies have reached their maximum potential and further advancements would require the development of new accelerator concepts, possibly based on more compact and cost-effective methods. Promising emerging techniques, such as laser-driven and beam-driven plasma acceleration, have the potential to reestablish the exponential trend in the energy growth depicted by the Livingston plot. Plasma wakefield accelerator relies on a coherent charge density oscillation in a plasma to provide the accelerating force. The plasma oscillation is driven by an externally injected short pulse, which can be either a laser (LWFA [3]) or an electron beam (PWFA [4]), which blows outward the electrons in an ionized gas (plasma), leaving behind a region of positive charge, as shown in Figure 2. Along the axis where the beam propagates, the electric field causes a trailing pulse of electrons injected near the rear of the bubble to feel a very strong forward acceleration. Gradient up to $1 0 0 \\mathrm { ~ G V / m }$ have been observed in several experiments [5]. Difficulties in the plasma scheme arise from the small scales involved (sub-mm transverse diameter), required micrometer tolerances and stability which may cause beam quality degradation with respect to conventional accelerators. But in recent time the plasma generated beam quality has advanced sufficiently to reach the requirements for driving a Free Electron Laser (FEL). There have been several reports of pilot free-electron lasing in plasma-based accelerators: one relying on LWFA by a team in China [6] and one relying on PWFA by the EuPRAXIA team in Frascati [7,8], Italy. Another experiment run by a French and German team has also recently confirmed seeding of the FEL process in a LWFA plasma accelerator [9]. | 2 | NO | 0 |
IPAC | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | THE AWAKE EXPERIMENT AWAKE is an R&D experiment at CERN with the aim to develop proton-driven based plasma wakefield acceleration. The wakefields are driven by highly-relativistic ${ \\mathrm { 4 0 0 G e V } }$ , relativistic factor $\\gamma _ { p + } \\sim 4 2 7 )$ and energetic $( > 1 9 \\mathrm { k J } )$ proton bunches, supplied by the CERN Super Proton Synchrotron (SPS). Since these proton bunches are longer than the plasma wavelength $\\lambda _ { p e }$ (where $\\lambda _ { p e } = 2 \\pi c / \\omega _ { p e }$ , with $\\omega _ { p e } = \\sqrt { n _ { p e } e ^ { 2 } / \\epsilon _ { 0 } m _ { e } }$ is the plasma electron frequency, $c$ the speed of light, $m _ { e }$ the electron mass, $e$ the electron charge, $\\epsilon _ { 0 }$ the vacuum permittivity and $n _ { p e }$ the plasma electron density) and less dense than the plasma $\\hat { ( n _ { b } < \\sim 1 0 ^ { - 3 } n _ { p e } }$ where $n _ { b }$ is the bunch density), the proton bunches have to be self-modulated to excite wakefields with $\\mathrm { G V / m }$ amplitudes [1, 2]; this requires $n _ { p e } > 1 0 ^ { 1 4 } \\mathrm { c m } ^ { - 3 }$ (corresponding to $\\lambda _ { p e } < 3 \\mathrm { m m } )$ ). The plasma is created by laser ionisation (pulse length: ${ \\sim } 1 0 0$ fs, energy per pulse: $\\sim 1 0 0 \\mathrm { m J }$ , central wavelength: $8 0 0 \\mathrm { n m }$ ) of rubidium vapour [3, 4]. It is $1 0 \\mathrm { m }$ long, with a radius $> \\sim 1 \\mathrm { m m }$ . Seeded proton bunch selfmodulation and subsequent wakefield growth, as well as the acceleration of externally injected witness electrons was demonstrated in AWAKE Run 1 [5–7]. | 1 | NO | 0 |
expert | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | The beam has geometric transverse emittances of $\\varepsilon _ { x } = 9 . 5 \\times 1 0 ^ { - 1 0 } \\mathrm { m }$ and $\\varepsilon _ { y } = 1 . 2 \\times 1 0 ^ { - 1 0 } \\mathrm { m }$ . It is focused with a quadrupole doublet to a spot with $1 0 \\mu \\mathrm { m }$ radius at the entrance of the plasma. With this beam energy, bunch length and spot size, the corresponding power density is $3 \\times 1 0 ^ { 2 0 } \\mathrm { W } \\mathrm { c m } ^ { - 2 }$ . Plasma generation. A column of lithium vapour with a density of $2 . 7 \\times 1 0 ^ { 1 7 } \\mathrm { c m } ^ { - 3 }$ is produced in a heat-pipe oven21. The lithium vapour is confined by a helium buffer gas, which is in turn separated from the beam-line vacuum by a $5 0 \\mathrm { - } \\mu \\mathrm { m }$ -thick beryllium window upstream and by a $7 5 \\mathrm { - } \\mu \\mathrm { m }$ -thick beryllium window downstream. Lithium was chosen because of the low ionization potential of its first electron $( 5 . 4 \\mathrm { e V } )$ and the relatively high potential for its two subsequent electrons (76 and $1 2 2 \\mathrm { e V }$ ). In the present experiments the transverse electric field of the ultrashort electron pulses is large enough to field-ionize the first lithium electron over a timescale shorter than the bunch duration. The ADK theory for field ionization22 indicates that full ionization occurs in the volume surrounding the pulse in which the electric field exceeds ${ \\sim } 6 \\mathrm { G V m } ^ { - 1 }$ . | 5 | NO | 1 |
IPAC | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | Plasma wakefield accelerators must be able to replicate the performance of large particle accelerators to be viable for applications in colliders and light sources. Both applications require high-quality electron beams with low emittance. The incoming electron beam possesses a divergence in the transverse direction inversely proportional to the $\\beta ^ { * }$ of the final focus. Conversely, the plasma will create a focusing force with strength determined by the plasma density; however, if the scales of these two effects are not properly matched, the energy spread of the electron beam will drive emittance growth. Unfortunately, the focusing force in a fully ionized plasma column is sufficiently strong that focusing the beam to the transverse size required for matching is not feasible with conventional magnetic optics. It has been shown theoretically and experimentally that introducing a plasma density ramp can properly match the electron beam and preserve emittance [4–9]. At the Facility for Advanced Accelerator Experimental Tests (FACET-II), we preionize hydrogen gas using a laser with a tailored longitudinal intensity profile, creating a plasma density ramp of customizable length. Laser-ionizing plasma has a few distinct advantages over the beam-ionized lithium-vapor oven used in previous FACET-II experiments. The heating of the lithium oven due to the energy deposited by the drive beam will change the plasma density profile, limiting the maximum repetition rate. Moreover, beamionized sources suffer from head erosion while this issue is avoided with preionized sources. Most importantly, the density ramps created by the lithium vapor are set in length and are too short to properly match the $\\beta ^ { * }$ from the final focus of the beam-line, causing emittance growth. Laser-ionized sources can create nearly any plasma density ramp desired by using the proper focusing optic. | 4 | NO | 1 |
expert | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | At each of the two planes, the particle distribution is measured by imaging Cherenkov radiation emitted as the electrons pass through a $1 5 \\mathrm { - m m }$ -wide air gap established by two silicon wafers (not shown in Fig. 1), positioned at an angle of $4 5 ^ { \\circ }$ to the beam. The second wafer acts as a mirror and deflects the Cherenkov light into a lens that images the origin of the light onto a cooled charge-coupled device camera (CCD). The electrons pass the silicon almost unperturbed. A system of equations is set up relating the offsets at the two planes to two angles, the exit angle at the plasma $\\theta _ { 0 }$ and the deflection angle in the magnet $\\theta _ { 1 }$ (see Fig. 1). For each feature in the spectrum that can be identified on both screens, for instance scalloping of the beam shown in Fig. 2a, this system of equations has been solved for $\\theta _ { 0 }$ and $\\theta _ { 1 }$ , the latter angle giving the particle energy. The highest-energy feature that can clearly be resolved (see Fig. 2a) is used to determine the energy gain for this event. The uncertainty in the energy measurement is dominated by the uncertainty in the determination of the position of this feature. | augmentation | NO | 0 |
expert | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | File Name:Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf Energy doubling of 42 GeV electrons in a metre-scale plasma wakefield accelerator Ian Blumenfeld1, Christopher E. Clayton2, Franz-Josef Decker1, Mark J. Hogan1, Chengkun Huang2, Rasmus Ischebeck1, Richard Iverson1, Chandrashekhar Joshi2, Thomas Katsouleas3, Neil Kirby1, Wei Lu2, Kenneth A. Marsh2, Warren B. Mori2, Patric Muggli3, Erdem ${ \\mathsf { O } } z ^ { 3 }$ , Robert H. Siemann1, Dieter Walz1 & Miaomiao Zhou2 The energy frontier of particle physics is several trillion electron volts, but colliders capable of reaching this regime (such as the Large Hadron Collider and the International Linear Collider) are costly and time-consuming to build; it is therefore important to explore new methods of accelerating particles to high energies. Plasma-based accelerators are particularly attractive because they are capable of producing accelerating fields that are orders of magnitude larger than those used in conventional colliders1–3. In these accelerators, a drive beam (either laser or particle) produces a plasma wave (wakefield) that accelerates charged particles4–11. The ultimate utility of plasma accelerators will depend on sustaining ultrahigh accelerating fields over a substantial length to achieve a significant energy gain. Here we show that an energy gain of more than $4 2 \\mathbf { G e V }$ is achieved in a plasma wakefield accelerator of ${ \\bf 8 5 c m }$ length, driven by a $4 2 \\mathbf { G e V }$ electron beam at the Stanford Linear Accelerator Center (SLAC). The results are in excellent agreement with the predictions of three-dimensional particle-in-cell simulations. Most of the beam electrons lose energy to the plasma wave, but some electrons in the back of the same beam pulse are accelerated with a field of ${ \\sim } 5 2 \\mathrm { G V } \\mathrm { m } ^ { - 1 }$ . This effectively doubles their energy, producing the energy gain of the 3-km-long SLAC accelerator in less than a metre for a small fraction of the electrons in the injected bunch. This is an important step towards demonstrating the viability of plasma accelerators for high-energy physics applications. | augmentation | NO | 0 |
expert | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | Thus, the full ionization extends over a radius of more than $1 0 0 \\mu \\mathrm { m }$ and ionization begins far earlier than the peak of the bunch current. Because the ionization region extends over a radius larger than the plasma collisionless skin depth $c / \\omega _ { \\mathrm { p } } ,$ where $\\omega _ { \\mathrm { p } } = ( n _ { \\mathrm { e } } e ^ { 2 } / \\varepsilon _ { 0 } m _ { \\mathrm { e } } ) ^ { 1 / 2 }$ is the plasma angular frequency; $e$ is the charge on the electron, $\\scriptstyle { \\varepsilon _ { 0 } }$ is the permittivity of free space and $m _ { \\mathrm { e } }$ is the mass of the electron), the wake is similar to that in a preformed plasma. Energy measurement. The energy spectrometer consists of a dipole magnet that disperses the electrons vertically according to their momentum $\\boldsymbol { p }$ . The dispersion can be closely approximated by a deflection at the centre of the magnet: $\\theta _ { 1 } = e \\int B \\mathrm { d } L / p$ . Using the measured dispersion, its integrated magnetic flux density #BdL was calculated to be $1 . 2 \\mathrm { T m }$ . In general, all particles in a pulse leave the plasma from a well-defined spot, but with a non-negligible exit angle $\\theta _ { 0 }$ . To discriminate between a vertical exit angle and the deflection by the magnet, the particle distribution is measured at two planes, $8 6 \\mathrm { c m }$ and $1 8 6 \\mathrm { c m }$ downstream of the centre of the dipole (Fig. 1). | augmentation | NO | 0 |
expert | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | In a plasma wakefield accelerator large-amplitude electric fields result from space-charge waves excited by the passage of an ultrarelativistic electron beam through a plasma12. A fully ionized plasma can be formed in a neutral vapour when the radial electric field of the electron beam exceeds the field ionization threshold13. The ionization occurs in a narrow region in the front of the beam. This ionization front produces a plasma that has a radius much larger than the beam itself. If the beam density exceeds the plasma density, the plasma electrons are expelled from the volume of the electron pulse, leaving a column of more massive ions behind14. Subsequently, the expelled plasma electrons are pulled back (by the ions) to the beam axis behind the pulse, overshoot, and set up a space-charge oscillation or wake. The longitudinal field of this wake varies continuously along the pulse, decelerating its core but accelerating the particles in the back. The ion column also provides a focusing force15 that guides the beam over many diffraction lengths, allowing an efficient transfer of the beam energy to the wake. This force also causes the transverse size of the beam to oscillate as it propagates through the plasma—the socalled betatron oscillations (see Supplementary Movie 1). | augmentation | NO | 0 |
expert | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | We used simulations to explain the maximum electron energy observed in the experiment. Figure 2b shows a comparison of the measured energy spectrum with one derived from simulations. The electron current distribution is extracted from the energy spectrum of the beam measured upstream of the plasma by comparing it to a phase space simulation using the code LiTrack17. The wakefield from this current distribution and the propagation of the pulse through the plasma are modelled using the three-dimensional, parallel particle-in-cell (3D-PIC) code QuickPIC18. QuickPIC includes the effects of field ionization and electron energy loss due to radiation19 from oscillations in the ion column. Figure 3a and b shows the simulation output at two different positions in the plasma. At a distance of $1 2 . 3 \\mathrm { c m } .$ , the wake produced by the motion of the plasma electrons resembles that produced in a preformed plasma, because the ionization occurs near the very head of the beam. The expelled plasma electrons return to the beam axis at nearly the same $z$ location. This gives rise to an extremely large spike in the accelerating field. After $8 1 . 9 \\mathrm { c m }$ one can see the effect of beam head erosion in that the ionization front now occurs further back along the pulse. Even though the wake is formed further back, the peak accelerating field occurs at approximately the same position along the pulse. The transverse size of the pulse ahead of the ionization front is so large that the local beam density has dropped below the useful range in the colour table. However, the modified ionization front causes some blurring of the position at which the returning plasma electrons arrive on the axis, an effect known as phase mixing. This not only reduces the peak accelerating field but also leads to some defocusing of the high-energy beam electrons in this region (see Supplementary Discussion and Supplementary Figs 1–4). | augmentation | NO | 0 |
expert | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | Recent plasma wakefield accelerator experiments have shown high-gradient acceleration of electrons using a 10-cm-long plasma11. To obtain energy gains of interest to high-energy physics, these high gradients must be extended over metre-scale plasmas. Such an extension transitions the plasma wakefield accelerator from a regime in which the drive beam has no time to distort, deplete or go unstable, to a regime in which it is significantly depleted in energy, deformed owing to combined effects of diffraction and multiple transverse oscillations, and possibly goes unstable because of the electron-hose instability16. This work is in this latter regime. A schematic of the experimental set-up is shown in Fig. 1. In the present work carried out at the Final Focus Test Beam facility at SLAC, the nominally 50-femtosecond-long electron beam containing $1 . 8 \\times { { 1 0 } ^ { 1 0 } }$ particles is focused to a spot size of ${ \\sim } 1 0 \\mu \\mathrm { m }$ at the entrance of an $8 5 \\mathrm { - c m }$ -long column of lithium vapour with a density $n _ { \\mathrm { e } }$ of $2 . 7 \\times 1 0 ^ { 1 7 } \\mathrm { c m } ^ { - 3 }$ . The nominally $4 2 \\mathrm { G e V }$ beam has a correlated energy spread of approximately $1 . 5 \\mathrm { G e V }$ , with electrons in the front of the beam at higher energies than those at the back. The beam exiting the plasma traverses a metre-long dipole magnet, which disperses the beam electrons according to their energy. The transverse distribution of the dispersed electrons is measured at two distances (planes 1 and 2 in Fig. 1) downstream of the dipole magnet to distinguish the energy changes of the electrons from their possible transverse deflection due to the plasma. | augmentation | NO | 0 |
expert | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | Images of the dispersed electrons are recorded along with the relevant beam parameters on a shot-to-shot basis. The energy gain achieved for each shot is determined as described in the Methods section. Figure 2 shows one example of the electron energy distribution between 35 and $1 0 0 \\mathrm { G e V }$ after traversing the plasma. The angle $\\theta _ { 0 }$ at the plasma exit for this particular event was calculated to be smaller than $1 0 0 \\mu \\mathrm { r a d }$ , which is negligible; therefore energy relates directly to position. The highest electron energy is $8 5 \\pm 7 \\mathrm { G e V } _ { \\mathrm { ; } }$ , indicating that some electrons in the tail of the beam with an initial energy of 41 GeV have more than doubled their initial energy. The implied peak accelerating field of ${ \\sim } 5 2 \\mathrm { G V } \\mathrm { m } ^ { - 1 }$ is consistent with the fields previously measured in a $1 0 \\mathrm { - c m }$ -long plasma11, indicating that the energy gain is scalable by extending the length of the plasma at least up to $8 5 \\mathrm { c m }$ . With this plasma length, in a series of 800 events, $3 0 \\%$ showed an energy gain of more than $3 0 \\mathrm { G e V }$ . Variations in the measured energy gain were correlated to fluctuations in the peak current of the incoming electron beam. | augmentation | NO | 0 |
expert | Why is lithium used in plasma wakefield accelerators | Because of its low ionization potential | Fact | Blumenfeld_et_al._-_2007_-_Energy_doubling_of_42_GeV_electrons_in_a_metre-scale_plasma_wakefield_accelerator.pdf | When the length of the lithium vapour column was extended from $8 5 \\mathrm { c m }$ to $1 1 3 \\mathrm { c m }$ , the maximum energy in an event with a similar incoming current profile was measured to be $7 1 \\pm 1 1 \\mathrm { G e V }$ . Less than $3 \\%$ of a sample of 800 consecutive events showed an energy gain of more than $3 0 \\mathrm { G e V }$ . There are three possible reasons for this apparent saturation of energy gain observed in the experiment. The first is that the energy of the particles that produced the wake has been depleted to almost zero, such that the acceleration is terminated in the last $2 8 \\mathrm { c m }$ of the plasma. However, the minimum energy measured at plane 1 (not shown) was $5 { \\mathrm { - } } 7 { \\mathrm { G e V } } ;$ , which is inconsistent with this explanation. The second possible reason is that the electron hosing instability is so severe that the beam breaks $\\mathrm { u p } ^ { 1 6 }$ . In the data shown in Fig. 2 there are negligible transverse deflections of the various longitudinal slices of the beam, indicating an absence of the hosing instability. The third possibility is head erosion: the front of the beam expands, because it is not subjected to the focusing force of the ion column. This expansion decreases the beam density, which moves the ionization front backward in the beam frame. Eventually the beam electric field drops below the threshold for plasma formation, terminating the acceleration process before the energy of the drive beam is depleted (see Supplementary Movie 1). | augmentation | NO | 0 |
expert | Why the CpFM features to identical fused silica bars? | One bar is devoted to the direct beam flux measurement , the other one to the background characterisation. | Fact | CpFM_paper.pdf | Finally, particular attention has to be paid to the shape of the distributions in Fig. 9(b). They are not Gaussian. For such a high fluxes, this cannot depend on the detector resolution, at least for the CpFM 2 channel which has the better efficiency. This can be demonstrated deriving the CpFM 2 resolution for an incident and constant flux of 180 protons per turn, as measured by the BCTDC. From the single ion distributions in Fig. 6(a), the resolution with respect to a single incident lead ion can be computed. The CpFM 2 resolution for 180 protons is easily derived scaling the ion resolution by the factor $\\sqrt { ( 6 7 2 4 / 1 8 0 ) }$ . It corresponds to $9 \\%$ . Thus, if the number of protons extracted by the crystal was constant and equal to 180 (distributed according a Gaussian distribution centered in 180), the CpFM 2 signal would be characterized by a narrower peak having 15 protons $\\sigma$ . The beam extracted by the crystal is therefore not constant on the time scale probed by the CpFM. There are several possible reasons for this: the diffusion dynamics of the halo beam, goniometer instabilities or orbit instabilities. The CpFM detector offers an interesting chance to address this issue at the μs scale but the current data acquisition electronics of the detector represent a limit. The CpFM detector is indeed able to accept only 1/1000 SPS trigger, since the data acquisition electronics are not fast enough $( < 1 \\mathrm { k H z } )$ . Faster electronics, matching the revolution frequency of the machine, could strengthen the detector capability in studying the impact of the listed factors on the crystal halo extraction. | 1 | Yes | 0 |
expert | Why the CpFM features to identical fused silica bars? | One bar is devoted to the direct beam flux measurement , the other one to the background characterisation. | Fact | CpFM_paper.pdf | beam profile monitors) Cherenkov detectors In-vacuum detectors High-energy particle accelerators A B S T R A C T The UA9 Experiment at CERN-SPS investigates channeling processes in bent silicon crystals with the aim to manipulate hadron beams. Monitoring and characterization of channeled beams in the high energy accelerators environment ideally requires in-vacuum and radiation hard detectors. For this purpose the Cherenkov detector for proton Flux Measurement (CpFM) was designed and developed. It is based on thin fused silica bars in the beam pipe vacuum which intercept charged particles and generate Cherenkov light. The first version of the CpFM is installed since 2015 in the crystal-assisted collimation setup of the UA9 experiment. In this paper the procedures to make the detector operational and fully integrated in the UA9 setup are described. The most important standard operations of the detector are presented. They have been used to commission and characterize the detector, providing moreover the measurement of the integrated channeled beam profile and several functionality tests as the determination of the crystal bending angle. The calibration has been performed with Lead $\\left( \\mathrm { P b } \\right)$ and Xenon (Xe) beams and the results are applied to the flux measurement discussed here in detail. | 1 | Yes | 0 |
expert | Why the CpFM features to identical fused silica bars? | One bar is devoted to the direct beam flux measurement , the other one to the background characterisation. | Fact | CpFM_paper.pdf | 5.2.1. Channeled beam profile In the channeling plateau, the linear scan shown in Fig. 8(b) basically corresponds to integrate the channeled beam profile in the horizontal plane. Therefore it can be fitted with an error function: $$ e r f ( x ) = A \\cdot { \\frac { 1 } { \\sigma { \\sqrt { 2 \\pi } } } } \\int _ { 0 } ^ { x } e ^ { - { \\frac { ( t - c ) ^ { 2 } } { 2 \\sigma ^ { 2 } } } } d t + K $$ Where $\\sigma$ is the standard deviation of the Gaussian beam profile, $\\scriptstyle { c }$ is the center of the channeled beam with respect to the primary one and $A$ and $K$ are constants related to the channeling plateau value and the background value. In Fig. 8(b) CpFM 1 and CpFM 2 linear scan profiles of Fig. 8(b) have been fitted with the error function described in Eq. (3). From the results of the fits the channeled beam size $( \\sigma )$ at the position of the CpFM is obtained as well as some informations confirming the functionality of the detector: both the CpFM 1 and CpFM 2 measure compatible values of the channeled beam standard deviation $( \\sigma )$ and, as expected, the difference between the channeled beam center (c) measured by the CpFM 1 and the CpFM 2 is compatible with the design distance between CpFM 1 and CpFM 2 bar edges. | 2 | Yes | 0 |
expert | Why the CpFM features to identical fused silica bars? | One bar is devoted to the direct beam flux measurement , the other one to the background characterisation. | Fact | CpFM_paper.pdf | File Name:CpFM_paper.pdf Commissioning and operation of the Cherenkov detector for proton Flux Measurement of the UA9 experiment F.M. Addesa a,∗, D. Breton d, L. Burmistrov d, G. Cavoto a,b, V. Chaumat d, S. Dubos d, L. Esposito c, F. Galluccio e, M. Garattini c,g, F. Iacoangeli a, J. Maalmi d, D. Mirarchi c, S. Montesano c, A. Natochii $^ { \\mathrm { c , d , f } }$ , V. Puill d, R. Rossi c, W. Scandale c, A. Stocchi d a INFN - Istituto Nazionale di Fisica Nucleare - sezione di Roma, Piazzale A. Moro 2, Roma, Italy b Università degli Studi di Roma "La Sapienza" -Department of Physics, Piazzale A. Moro 2, Roma, Italy c CERN, European Organization for Nuclear Research, Geneva 23, CH 1211, Switzerland d LAL - Laboratoire de l’Accélérateur Linéaire - Université Paris-Sud 11, Centre Scientifique d’Orsay, B.P. 34, Orsay Cedex, F-91898, France e INFN Sezione di Napoli, Complesso Universitario di Monte Sant’Angelo, Via Cintia, 80126 Napoli, Italy f Taras Shevchenko National University of Kyiv (TSNUK), 60 Volodymyrska Street, City of Kyiv, 01033, Ukraine g Imperial College, London, United Kingdom A R T I C L E I N F O Keywords: Beam instrumentation (beam flux monitors, | augmentation | Yes | 0 |
expert | Why the CpFM features to identical fused silica bars? | One bar is devoted to the direct beam flux measurement , the other one to the background characterisation. | Fact | CpFM_paper.pdf | 1. Introduction The primary goal of the UA9 experiment [1] is to demonstrate the feasibility of a crystal-based halo collimation as a promising and better alternative to the standard multi-stage collimation system for high-energy hadron machines. The main installation of the experiment is located in the Long Straight Section 5 (LSS5) of the CERN Super Proton Synchrotron (SPS) and consists of a crystal-assisted collimation prototype. It is made by preexisting optical elements of the SPS and new installations including three goniometers to operate different crystal types used as primary collimators, one dedicated movable absorber, several scrapers, detectors and beam loss monitors (BLMs) to study the interaction of the crystal with the beam halo [3]. A schematic of the layout of the experiment is shown in Fig. 1. The main process investigated is the so-called planar channeling: particles impinging on a crystal having a small angle (less than $\\theta _ { c }$ , called the critical angle for channeling) with respect to the lattice planes are forced by the atomic potential to move between the crystal planes. If the crystal is bent, the trapped particles follow the bending and are deflected correspondingly. When an optimized crystal intercepts the beam halo to act as collimator, about $8 0 \\%$ of the particles are channeled, coherently deflected and then dumped on the absorber (see Fig. 1), effectively reducing the beam losses in the sensitive areas of the accelerator [4–7]. | augmentation | Yes | 0 |
expert | Why the CpFM features to identical fused silica bars? | One bar is devoted to the direct beam flux measurement , the other one to the background characterisation. | Fact | CpFM_paper.pdf | 3.2. PMT gain optimization While choosing the PMT gain for both proton and ion runs, the maximum expected flux has to be considered together with the photoelectron yield per charge and the WaveCatcher dynamic range. To determine the optimal gain is noticed that the saturation of the ADC occurs at $2 . 5 \\mathrm { V }$ . The typical proton beam setup during UA9 experiments is a single 2 ns long bunch of $1 . 1 5 \\times 1 0 ^ { 1 1 }$ protons stored in the machine at the energy of $2 7 0 \\mathrm { G e V }$ [14]. For this beam intensity, the beam flux deflected by the crystal toward the CpFM ranges from 1 up to $\\simeq 2 0 0$ protons per turn (every ${ \\sim } 2 3 ~ \\mu \\mathrm { s } .$ ), depending on the aperture of the crystal with respect to the beam center. In this case the optimal PMT gain is $5 \\times 1 0 ^ { 6 }$ corresponding to bias the PMT at $1 0 5 0 \\mathrm { V } .$ . When the PMT is operated at such a gain a $S _ { p h . e }$ corresponds to $\\mathord { \\sim } 1 5 \\mathrm { \\ m V }$ (Fig. 3); considering the calibration factor (0.62 photoelectron yield per charge, measured at BTF and H8 line) the average amplitude of the signal produced by 200 protons is much lower than the dynamic range of the digitizer, allowing furthermore a safety margin of about 70 protons per pulse. | augmentation | Yes | 0 |
expert | Why the CpFM features to identical fused silica bars? | One bar is devoted to the direct beam flux measurement , the other one to the background characterisation. | Fact | CpFM_paper.pdf | Using the value above and the value of the $\\sigma$ of the channeled beam obtained by the fit shown in Fig. 8(b), it is also possible to extrapolate the angular spread of the particles exiting the crystal. It can be derived subtracting the equivalent kick for $x _ { C p F M } = { \\bf c } \\pm \\sigma$ from $\\theta _ { b e n d }$ , corresponding to the equivalent kick calculated in the center $c$ of the channeled beam: $$ \\theta _ { s p r e a d } = [ \\theta _ { k } ] _ { c \\pm \\sigma } \\mp \\theta _ { b e n d } $$ applying the Eq. (5) to the fit results in Fig. 8(b), the angular spread has been evaluated to be: $\\theta _ { s p r e a d } = ( 1 2 . 8 \\pm 1 . 3 ) \\mu \\mathrm { r a d }$ . The angular spread at the exit of the crystal is directly connected to the critical angle value which defines the angular acceptance of the channeled particles at the entrance of the crystal. Therefore the angular spread should be comparable with respect to the critical angle. From theory [16], for $2 7 0 { \\mathrm { G e V } }$ protons in Si $\\theta _ { c }$ is $1 2 . 2 \\mu \\mathrm { r a d }$ .5 It can be then asserted that the angular spread derived by the fit results and the critical angle computed from the theory are well comparable. | augmentation | Yes | 0 |
expert | Why the CpFM features to identical fused silica bars? | One bar is devoted to the direct beam flux measurement , the other one to the background characterisation. | Fact | CpFM_paper.pdf | In Fig. 7 the angular scan of the UA9 crystal-1 during a proton run is shown. It is displayed both by the BLMs and the CpFM (CpFM position is such that both the bars intercept the whole channeled beam when the crystal is in the optimal channeling position). The first and the last angular regions (angle $< - 2 7 0 0$ μrad and angle $> - 2 4 0 0 ~ \\mathrm { \\mu r a d } )$ correspond to the amorphous orientation. As expected, here the loss rate registered by the BLMs is maximum while the CpFM signal rate is minimum. After the first amorphous region, the channeling peak appears (around angle of $- 2 6 2 0 \\ \\mu \\mathrm { r a d } )$ as a maximum in the CpFM rate and as minimum in the BLMs rate. Just after, only in the BLMs signal, the volume reflection area is clearly visible. In this angular region the particles experience a deflection to the opposite side with respect to the planar channeling deflection. For this reason volume reflection is not detectable by the CpFM except as a slight reduction in the background counts. Although the BLMs rate profile is an effective instrument for the estimation of the best channeling orientation, it is based on beam losses and is generally less sensitive than the CpFM rate profile which on the contrary measures directly the presence of channeled protons. | augmentation | Yes | 0 |
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