Triggering of tearing instability by impurity radiation through resistive interchange reversal in a tokamak

TL;DR

This paper demonstrates through MHD simulations that impurity radiation cooling can reverse the resistive interchange parameter, triggering tearing mode growth in tokamaks, with the process influenced by thermal conductivity.

Contribution

It reveals the mechanism by which impurity radiation induces tearing instability via resistive interchange reversal in tokamaks, highlighting the role of thermal conductivity.

Findings

Impurity radiation cooling can trigger tearing modes in tokamaks.

The impurity threshold for instability depends on parallel thermal conductivity.

Resistive interchange parameter reversal is key to mode growth.

Abstract

Recent MHD simulations find that the reversal of the local resistive interchange parameter $D_R$ from negative to positive due to impurity radiation cooling is able to trigger the resistive tearing mode growth in a tokamak above a threshold in impurity level. A layer of perturbed Pfirsch-Schl\"{u}ter current density and resistivity are also induced by the impurity radiation, which further govern the tearing mode growth and saturation in the nonlinear stage. The impurity threshold and the tearing mode growth strongly depend on the parallel thermal conductivity, and such a dependence derives from the impact on $D_R$ of the fast parallel thermal equilibration along the helical magnetic field lines.