Testing of the new JOREK stellarator-capable model in the tokamak limit

TL;DR

This paper extends the JOREK nonlinear MHD code to stellarators by deriving and testing a hierarchy of stellarator-capable models, ensuring they match tokamak models in the tokamak limit and conserve energy.

Contribution

The paper introduces a new reduced MHD model with alternative projection operators that matches standard tokamak models and conserves energy exactly.

Findings

The new model matches standard JOREK tokamak models in the tokamak limit.

The new model conserves energy exactly.

Momentum conservation is less accurate with the new operators when field-aligned flow is present.

Abstract

In preparation for extending the JOREK nonlinear MHD code to stellarators, a hierarchy of stellarator-capable reduced and full MHD models has been derived and tested. The derivation was presented at the EFTC 2019 conference. Continuing this line of work, we have implemented the reduced MHD model (arXiv:1907.12486) as well as an alternative model which was newly derived using a different set of projection operators for obtaining the scalar momentum equations from the full MHD vector momentum equation. With the new operators, the reduced model matches the standard JOREK reduced models for tokamaks in the tokamak limit and conserves energy exactly, while momentum conservation is less accurate than in the original model whenever field-aligned flow is present.