Sophia Henneberg (IPP Greifswald): Advances in Stellarator Optimization

Physikalisches Kolloquium

To achieve fusion, one can exploit the charged nature of plasma by using a magnetic field to confine it. There are two main approaches for magnetically confined fusion energy: The tokamak is an axisymmetric approach. The simplicity comes with a cost since tokamaks require a current in the plasma to generate the required magnetic field. Stellarators, on the other hand, possess three-dimensional magnetic fields typically solely generated by the coils’ magnetic field. This reduces or even eliminates the need for generating toroidal plasma currents, which can lead to detrimental instabilities such as disruptions. However, the three-dimensionality can in general involve some drawbacks, e.g., more complicated coils are typically needed compared to the axisymmetric case. Nonetheless, with careful exploitation of the large design space via optimization, the apparent disadvantages can be diminished.

Recent improvements in stellarator optimization will be presented: In stellarator optimization studies, the boundary of the plasma is usually described by Fourier series that are not unique: several sets of Fourier coefficients describe approximately the same boundary shape. A simple method for eliminating this arbitrariness is proposed and shown to work well in practice. Additionally, we investigate the mathematical structure of the various inter-related calculations that underpin the integrated stellarator optimization problem to better understand how the equilibrium calculation, the coil calculation, and the optimization calculation communicate with each other. Last, new exciting stellarator designs with better confinement properties will be presented.

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