A current driven electromagnetic mode in sheared and toroidal configurations

TL;DR

This paper investigates a current-driven electromagnetic mode in sheared and toroidal plasma configurations, revealing how induced electric fields can destabilize kink modes in tokamaks through gyrokinetic modeling.

Contribution

The study introduces a new gyrokinetic simulation approach to analyze the destabilizing effects of induced electric fields on plasma stability in tokamaks.

Findings

Identification of high mode number kink modes in simulations

Agreement between simulation results and analytical theory

Demonstration of the destabilizing influence of current on plasma stability

Abstract

The induced electric field in a tokamak drives a parallel electron current flow. In an inhomogeneous, finite beta plasma, when this electron flow is comparable to the ion thermal speed, the Alfven mode wave solutions of the electromagnetic gyrokinetic equation can become nearly purely growing kink modes. Using the new "low-flow" version of the gyrokinetic code GS2 developed for momentum transport studies [Barnes et al 2013 Phys. Rev. Lett. 111, 055005], we are able to model the effect of the induced parallel electric field on the electron distribution to study the destabilizing influence of current on stability. We identify high mode number kink modes in GS2 simulations and make comparisons to analytical theory in sheared magnetic geometry. We demonstrate reassuring agreement with analytical results both in terms of parametric dependences of mode frequencies and growth rates, and regarding the radial mode structure.