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ConStellaration: A dataset of QI-like stellarator plasma boundaries and optimization benchmarks
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Releases ConStellaration, a ~158k-sample dataset of QI-like stellarator plasma boundaries with VMEC++ ideal-MHD equilibria, three optimization benchmarks with classical baselines, and an MCMC-based generative sampler of feasible configurations.
Problem
Stellarator stage-one design is a high-dimensional constrained optimization problem with expensive physics simulations, and lacks standardized benchmarks and datasets for data-driven methods, especially for quasi-isodynamic (QI) configurations.
Approach
Generate a large dataset of diverse QI-like plasma boundaries by sampling omnigenous target fields and optimizing boundaries with DESC and VMEC++, then define three constrained benchmarks (geometric, simple-to-build QI, MHD-stable QI) with classical baselines and a PCA+random-forest+GMM+MCMC generator that samples feasible shapes without the physics oracle.
Key results
- ALM-NGOpt was the only baseline to find feasible solutions; geometric problem score 0.969 and simple-to-build score 0.431, MHD-stable score 130.0.
- MLP ensemble predicts target metrics from boundary coefficients with R^2 > 0.97 and RMSE < 0.1 for all metrics on the held-out set.
- The dataset contains about 158k evaluated configurations, with 1 to 5 field periods (15k, 20k, 68k, 27k, 28k respectively).
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use ALM-NGOpt instead of scipy-trust-constr or scipy-COBYQA | Classical stellarator optimization baselines · Geometric and simple-to-build QI problems | feasibility | Helped |
| Train an MLP ensemble on boundary coefficients to predict target metrics | QI-like stellarator dataset · Held-out test set | R² across predicted metrics: R²>0.97 | Helped |
| Use PCA, Random Forest feasibility classifiers, a GMM prior, and adaptive MCMC sampling | Feasible configuration generation · Relaxed geometric and simple-to-build QI problems | oracle-confirmed feasible configuration generation | Helped |
Surprising findings
- Both SciPy-based optimizers (trust-constr and COBYQA) failed to produce feasible solutions on the benchmarks, with only the ALM-NGOpt gradient-free method succeeding.
- Only 41 and 52 feasible points existed in the dataset for the relaxed geometric and simple-to-build problems (out of ~160k), motivating the generative sampler.
Limitations
- The degree of QI in the dataset is limited by the finite-budget optimization-based sampling process.
- The dataset covers only plasma boundaries and not electromagnetic coils or other reactor systems.
- Surrogate models are prone to extrapolation errors far from the training distribution.
Experimental setup
Datasets: ConStellaration dataset (~158k QI-like boundaries)
Benchmarks: ConStellaration optimization benchmarks (geometric, simple-to-build QI, MHD-stable QI)
Metrics: max elongation minimum normalized magnetic gradient scale length hypervolume normalized constraint violation RMSE R^2 NRMSE SNR
Baselines: scipy-trust-constr scipy-COBYQA ALM-NGOpt
Builds on: VMEC VMEC++ DESC SIMSOPT pyQSC
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