Optimizing stellarators to the infinite-n ideal ballooning mode with an adjoint method

We have developed an infinite-n, ideal-ballooning solver for general 3D MHD equilibria. This solver is based on the numerical scheme developed by Sanchez et al for the ballooning code COBRAVMEC. Unlike COBRAVMEC, our code also scans each surface for multiple values of the ballooning parameter to find the maximum growth rate. We present tests for various 2D and 3D equilibria.

One commonly uses gradient-based optimization to optimize stellarators against the ideal-ballooning mode. This can be computationally expensive for a large number of input parameters. To alleviate this, we present an adjoint method for optimizing stellarator equilibria against the ideal-ballooning mode. Our study will be focused on quasisymmetric configurations. We aim to maximize the operational beta value while ensuring ideal-ballooning stability on all surfaces. We present our results for different 3D equilibria.