Single-stage gradient-based stellarator coil design: Optimization for near-axis quasi-symmetry
| Autor: | Andrew Giuliani, Florian Wechsung, Antoine Cerfon, Georg Stadler, Matt Landreman |
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| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
Numerical Analysis
Physics and Astronomy (miscellaneous) Applied Mathematics FOS: Physical sciences Numerical Analysis (math.NA) Computational Physics (physics.comp-ph) Physics - Plasma Physics Computer Science Applications Plasma Physics (physics.plasm-ph) Computational Mathematics Optimization and Control (math.OC) Modeling and Simulation FOS: Mathematics Mathematics - Numerical Analysis Mathematics - Optimization and Control Physics - Computational Physics |
| Popis: | We present a new coil design paradigm for magnetic confinement in stellarators. Our approach directly optimizes coil shapes and coil currents to produce a vacuum quasi-symmetric magnetic field with a target rotational transform on the magnetic axis. This approach differs from the traditional two-stage approach in which first a magnetic configuration with desirable physics properties is found, and then coils to approximately realize this magnetic configuration are designed. The proposed single-stage approach allows us to find a compromise between confinement and engineering requirements, i.e., find easy-to-build coils with good confinement properties. Using forward and adjoint sensitivities, we derive derivatives of the physical quantities in the objective, which is constrained by a nonlinear periodic differential equation. In two numerical examples, we compare different gradient-based descent algorithms and find that incorporating approximate second-order derivative information through a quasi-Newton method is crucial for convergence. We also explore the optimization landscape in the neighborhood of a minimizer and find many directions in which the objective is mostly flat, indicating ample freedom to find simple and thus easy-to-build coils. 28 pages |
| Databáze: | OpenAIRE |
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