A Virtual Simons' Hour Talk:
Adjoint methods for quasisymmetry of vacuum fields on a surface

Given by: Richard Nies
Princeton Program in Plasma Physics,
Princeton Plasma Lab, Princeton, NJ

Note the time: 8:00am EDT / 12:00 UTC.  Zoom link will be sent via email.

Abstract:   Stellarator optimisation can be significantly sped up by using adjoint methods instead of finite-differences to obtain derivative information. In this work, we apply adjoint methods to stellarator vacuum fields, considering objective functions targeting quasisymmetry and rotational transform on the boundary. To define quasisymmetry on the surface, a novel way of constructing approximate flux coordinate on an isolated flux surface is proposed. The obtained adjoint equations are of a simple form such that they can be solved with existing numerical tools, and yield highly accurate derivatives. Using adjoint methods, we obtain configurations with highly accurate quasisymmetry on the boundary, and we are able to systematically investigate the interplay between quasisymmetry and other optimisation targets, such as the aspect ratio and rotational transform.