Kinetic microtearing modes and reconnecting modes in strongly magnetised slab plasmas

TL;DR

This paper investigates the linear microtearing mode in strongly magnetized slab plasmas, introducing a hybrid fluid-kinetic model for electrons and analyzing conditions for instability and reconnection.

Contribution

It presents a novel hybrid fluid-kinetic model for electrons, linking microtearing modes to reconnecting modes, and clarifies the conditions for instability in collisional regimes.

Findings

Identification of the breaking of the constant-A_parallel approximation as necessary for microtearing instability.

Development of an electron conductivity model matching Landau results and correct isothermal response.

Connection of microtearing modes with collisional and collisionless tearing-parity ETG modes.

Abstract

The problem of the linear microtearing mode in a slab magnetised plasma, and its connection to kinetic reconnecting modes, is addressed. Electrons are described using a novel hybrid fluid-kinetic model that captures electron heating, ions are gyrokinetic. Magnetic reconnection can occur as a result of either electron conductivity and inertia, depending on which one predominates. We eschew the use of an energy dependent collision frequency in the collisional operator model, unlike previous works. A model of the electron conductivity that matches the weakly collisional regime to the exact Landau result at zero collisionality and gives the correct electron isothermal response far from the reconnection region is presented. We identify in the breaking of the constant-$A_{\parallel}$ approximation the necessary condition for microtearing instability in the collisional regime. Connections with the theory of collisional non-isothermal (or semicollisional) and collisionless tearing-parity electron temperature gradient driven (ETG) modes are elucidated.