VMECdash

An interactive Dash application for exploring VMEC wout_*.nc stellarator equilibria.
It reconstructs magnetic surfaces with JAX, renders 1‑D/2‑D/3‑D plots and so on, motivated by the original MATLAB tool VMECplot.m.

Motivation: Quickly inspect the VMEC equilibrium quantities of interest without relying on difficult-for-starter-to-compile programs (such as libstell) or memory-heavy commercial software (such as MATLAB).

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Features

• File upload for standard VMEC wout NetCDF output.
• Summary dashboard with key scalar diagnostics and highlighted metadata (free/fixed boundary, mgrid file, etc.).
• 1‑D profiles for rotational transform, safety factor, pressure, volume derivative, beta metrics, and more.
• 2‑D visualisations:
  • R‑Z cross sections with geometry or interpolated scalar fields.
  • θ‑ζ flux-surface contours across a field period.
• 3‑D flux surfaces with optional coordinate‑free background shading.
• Field lines viewer for $\alpha-\zeta$ coordinates on selected flux
  • A nice choice for visualising magnetic ripple
  • 2D plots of $|B|(\alpha, \zeta)$
  • 1D plots of single period field line traces with different initial $\alpha$ values
  • Single field line transistions.
• JAX acceleration for geometry reconstruction.

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Requirements

Python 3.10+ is recommended. Install dependencies with conda:(optional)

conda activate your_env_name
pip install -r requirements.txt

Note for JAX: If you don't have a GPU/TPU or your gpu is not supported for FP64(like metal), then simply running pip install jax[cpu] to install the CPU-only version is good enough. GPU/TPU wheels require platform-specific instructions from the JAX documentation.

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Running the App

python VMECdash.py

Dash defaults to http://127.0.0.1:8050/. The layout is responsive, so you can resize the browser to focus on plots or the control sidebar.

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Usage Tips

1. Upload a VMEC NetCDF file (wout_*.nc) via the drag‑and‑drop area in the sidebar.
2. Use Visualization Mode to switch between:
   • Summary Dashboard (shows statistics + multi-panel plots),
   • 1D Profiles, 2D Cross Sections, 2D Flux Surfaces, and 3D Geometry.
3. Adjust sliders for toroidal angle (phi), flux surface index (s), and choose different physical quantities from the dropdowns.
4. Toggle Coordinate-free background in 3‑D mode for clean screenshots.
5. Click Download Plot to export the currently visible figure as a PNG.

The app caches equilibrium metadata, so switching modes or variables is fast.
For heavy 2‑D physics overlays, a pre-computation step runs on the server while keeping the UI responsive.

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Repository Layout

Path	Description
VMECdash.py	Main Dash entry point (layout + callbacks).
vmec_jax.py	JAX-powered data processor for VMEC equilibria.
views/	Modular UI components (overview, profiles, 2D/3D, fieldlines).
ui/	Shared UI helper components.
requirements.txt	Python dependencies.
example/wout_PO.nc	Example VMEC equilibrium (use your own files for new cases).

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TroubleShooting

Feel free to open issues or pull requests to add new physical quantities, UI tweaks, or performance optimisations. Enjoy exploring your VMEC equilibria!

Next step

• Add jax-based boozer coordinate transformation.
• Fast evaulation of EffetiveRipple, GammaC, maybe slow without gpu.