The gyrokinetic dispersion relation of microtearing modes in collisionless toroidal plasmas

TL;DR

This paper derives a fast-evaluating dispersion relation for microtearing modes in collisionless toroidal plasmas, revealing their instability driven by electron temperature gradients and magnetic drifts, with implications for fusion device stability.

Contribution

The paper presents a new, efficiently computable dispersion relation for microtearing modes in collisionless toroidal plasmas, incorporating magnetic drifts and temperature gradients.

Findings

MTMs are driven unstable by electron temperature gradients.

Magnetic drifts mediate the instability drive.

The dispersion relation can be evaluated quickly for practical use.

Abstract

We solve the linearized gyrokinetic equation, quasineutrality condition, and Ampere's law to obtain the dispersion relation of microtearing modes (MTMs) in collisionless low-beta toroidal plasmas. Consistent with past studies, we find that MTMs are driven unstable by the electron temperature gradient and that this instability drive is mediated by magnetic drifts. The dispersion relation that we derive can be evaluated numerically very quickly and may prove useful for devising strategies to mitigate MTM instability in fusion devices.