Direction of cascades in a magnetofluid model with electron skin depth and ion sound Larmor radius scales

TL;DR

This paper investigates cascade directions in a 2D magnetofluid model considering electron inertia and ion sound Larmor radius, revealing scale-dependent cascade behaviors and the impact of gyro-effects on energy distribution.

Contribution

It provides analytical expressions for equilibrium states and demonstrates how gyro-effects enable negative temperature states and energy condensation at large scales.

Findings

Energy and magnetic helicity cascade directly at scales below electron skin depth.

Helicity exhibits inverse cascade at large scales, consistent with reduced MHD.

Gyro-effects facilitate negative temperature states and energy condensation.

Abstract

The direction of cascades in a two-dimensional model that takes electron inertia and ion sound Larmor radius into account is studied, resulting in analytical expressions for the absolute equilibrium states of the energy and helicities. It is found that typically both the energy and magnetic helicity at scales shorter than electron skin depth have direct cascade, while at large scales the helicity has an inverse cascade as established earlier for reduced magnetohydrodynamics (MHD). It is also found that the introduction of gyro-effects allows for the existence of negative temperature (conjugate to energy) states and the condensation of energy to the large scales. Comparisons between two- and three-dimensional extended MHD models (MHD with two-fluid effects) show qualitative agreement between the two.