Approach for efficient linear MHD analysis without spectrum pollution in tokamaks

Aiba, Nobuyuki; Cooper, W.*; Gruber, R.*

We developed a new numerical method for analyzing linear ideal MHD stability with higher-order finite element. Since the linear ideal MHD problem is a typical ill-posed problem from numerical viewpoints, a kind of numerical instability, called spectrum pollution, sometimes appears. About 30 years ago, a method realizing to suppress this numerical instability was developed, but this cannot fully suppress this. In fact, when the radial mesh number decreases, numerical instability appears. After revisiting this method, we found that the numerical integral method in this method is not appropriate for suppressing this instability. To fix this issue, we developed a new method with Gauss-Legendre quadrature, and realized to fully suppress numerical instability. This method can apply to the stability analysis with plasma rotation.