Gyrokinetic simulations of the tearing instability

TL;DR

This paper uses linear gyrokinetic simulations to study the tearing instability, revealing how collisionality and kinetic effects influence growth rates and emphasizing the importance of kinetic physics in the collisionless regime.

Contribution

It provides a detailed gyrokinetic analysis of the tearing instability across collisional and collisionless regimes, highlighting the limitations of fluid theory and the role of kinetic effects.

Findings

Growth rate scaling matches two-fluid theory in low beta collisional regime.

Kinetic effects like Landau damping invalidate fluid theory in collisionless regime.

Scaling behaviors depend on the ion-to-electron temperature ratio and plasma beta.

Abstract

Linear gyrokinetic simulations covering the collisional -- collisionless transitional regime of the tearing instability are performed. It is shown that the growth rate scaling with collisionality agrees well with that predicted by a two-fluid theory for a low plasma beta case in which ion kinetic dynamics are negligible. Electron wave-particle interactions (Landau damping), finite Larmor radius, and other kinetic effects invalidate the fluid theory in the collisionless regime, in which a general non-polytropic equation of state for pressure (temperature) perturbations should be considered. We also vary the ratio of the background ion to electron temperatures, and show that the scalings expected from existing calculations can be recovered, but only in the limit of very low beta.