Simulations of poloidal flow stabilization of ballooning modes in a classical l=2 stellarator using JOREK

Abstract

Magnetohydrodynamics (MHD), combining fluid dynamics and Maxwell's equations, provides a useful means of analysing the dynamic evolution of plasmas and plasma instabilities. JOREK is a non-linear MHD code which solves these equations in the context of magnetic confinement fusion. Originally developed for tokamaks, JOREK has been extended to model stellarators. In this project, ExB poloidal flows are implemented in a classical l=2 stellarator configuration, by imposing a simple radial electric potential profile via initial conditions. The influence of this sheared background flow velocity on pressure-driven modes is interrogated, demonstrating a stabilizing effect when the shearing rate is comparable to the growth rate. This effect is observed for multiple toroidal modes and at different viscosities, demonstrating that the stabilization occurs as a result of shear decorrelation. Oscillations of the linear growth rate are observed in cases with higher flow speeds; this phenomenon is hypothesized to be due to phase misalignment between the poloidally coupled modes contributing to the ballooning mode. Some indicators are provided to support this, however analysis of this phenomenon is ongoing.