---
license: cc-by-4.0
language:
- en
pretty_name: SII Stellarator Configuration Dataset
tags:
- fusion
- stellarator
- quasi-isodynamic
- scientific-machine-learning
- tabular
---

# SII Stellarator Configuration Dataset

**Wenyang Li**

[**Shanghai Innovation Institute**](http://www.sii.edu.cn) | PhD student

[AI-Driven Controlled Fusion Simulation, Control & Design Lab](https://github.com/SII-AI4Fusion)

- **Phone**: [+86-156-2003-5216](tel:+86-156-2003-5216)
- **Email**: [lwydsg@mail.nankai.edu.cn](mailto:lwydsg@mail.nankai.edu.cn)

---

## Overview

This directory hosts a **stellarator configuration dataset grouped by number
of field periods (nfp)**. Each sample keeps only three things:
**Fourier boundary coefficients, nfp, and 9 VMEC evaluation metrics** —
every field is guaranteed to be non-`None` / non-`NaN`.

Design goals:

1. **Simplified content** — keep only the Fourier coefficients and the 9
   VMEC metrics that configuration-design optimization actually needs; all
   other construction parameters / diagnostics / multi-beta-branch
   evaluations are stripped out.
2. **Ready for future growth** — more QI (Quasi-Isodynamic) configurations
   will be folded in later, so a unified, clean, schema-stable baseline
   makes that painless.

## Source

Derived from a local copy of
[proxima-fusion/constellaration](https://huggingface.co/datasets/proxima-fusion/constellaration),
covering `n_field_periods` (nfp) = 1–5. The upstream library has broad
coverage but not every row has complete VMEC evaluation results; this
dataset keeps **only rows where every field is fully valid**.

## File layout

One file per nfp. The filename embeds the number of retained samples
`n{count}`:

| File | Samples | Note |
| --- | --- | --- |
| `nfp1_n14607.parquet` | 14,607 | nfp = 1 |
| `nfp2_n19945.parquet` | 19,945 | nfp = 2 |
| `nfp3_n68191.parquet` | 68,191 | nfp = 3 |
| `nfp4_n27798.parquet` | 27,798 | nfp = 4 |
| `nfp5_n28144.parquet` | 28,144 | nfp = 5 |
| **Total** | **158,685** | |

Parquet files use snappy compression with a flat column layout — they can
be loaded column-wise directly.

## Fields

Each row (one sample) has three groups of fields:

### 1. Field-period count `nfp`

- Column: `boundary.n_field_periods`
- Type: integer
- Meaning: number of toroidal field periods
- Values present in this dataset: 1, 2, 3, 4, 5

### 2. Fourier boundary coefficients `boundary.r_cos` / `boundary.z_sin`

- Type: 5×9 float matrix (`list<list<double>>`)
- Meaning: Fourier expansion coefficients of the stellarator boundary
  surface along the `(θ, φ)` periodic directions. `r_cos` is the cosine
  component of R; `z_sin` is the sine component of Z (the configuration is
  stellarator-symmetric, so only these two terms are retained).
- Shape convention: row index corresponds to the poloidal mode `m`
  (0…4, 5 rows); column index corresponds to the toroidal mode `n`
  (−4…+4, 9 columns).

### 3. VMEC evaluation metrics `metrics.*`

| Column | Meaning |
| --- | --- |
| `metrics.aspect_ratio` | Aspect ratio |
| `metrics.edge_rotational_transform_over_n_field_periods` | Edge iota / nfp (**no abs applied** — original sign preserved) |
| `metrics.average_triangularity` | Average triangularity |
| `metrics.max_elongation` | Maximum elongation |
| `metrics.edge_magnetic_mirror_ratio` | Edge magnetic mirror ratio |
| `metrics.vacuum_well` | Vacuum magnetic well |
| `metrics.minimum_normalized_magnetic_gradient_scale_length` | Minimum normalized magnetic gradient scale length |
| `metrics.qi` | Quasi-isodynamic residual (**no log10 applied** — raw value) |
| `metrics.flux_compression_in_regions_of_bad_curvature` | Flux compression in regions of bad curvature |

> For generality, `iota` is not abs-ed and `qi` is not log10-transformed —
> raw values are stored; downstream code applies whatever transform it
> needs.

## Full schema

Flat column names for straightforward column-wise access:

| Column | Type |
| --- | --- |
| `boundary.n_field_periods` | `int64` |
| `boundary.r_cos` | `list<list<double>>` (5×9) |
| `boundary.z_sin` | `list<list<double>>` (5×9) |
| `metrics.aspect_ratio` | `double` |
| `metrics.edge_rotational_transform_over_n_field_periods` | `double` |
| `metrics.average_triangularity` | `double` |
| `metrics.max_elongation` | `double` |
| `metrics.edge_magnetic_mirror_ratio` | `double` |
| `metrics.vacuum_well` | `double` |
| `metrics.minimum_normalized_magnetic_gradient_scale_length` | `double` |
| `metrics.qi` | `double` |
| `metrics.flux_compression_in_regions_of_bad_curvature` | `double` |

## Data-quality guarantee

Every sample satisfies:

1. `nfp` is neither `None` nor `NaN`;
2. The entire 5×9 matrices of `boundary.r_cos` and `boundary.z_sin` contain
   no `None` / `NaN`;
3. All **9 VMEC metrics** above are non-`None` and non-`NaN`.

Any sample failing any of these conditions was removed before inclusion.