Inertial range turbulence in kinetic plasmas

TL;DR

This paper develops a theoretical framework for understanding inertial range turbulence in kinetic plasmas, emphasizing the entropy cascade's role in converting turbulent energy into heat, with initial numerical results supporting this theory.

Contribution

It introduces a new theoretical foundation for kinetic plasma turbulence, highlighting the entropy cascade and proposing a simulation strategy.

Findings

Conservation of generalized energy in the cascade

Collisions are necessary for irreversible heating

Numerical results support the entropy cascade mechanism

Abstract

The transfer of turbulent energy through an inertial range from the driving scale to dissipative scales in a kinetic plasma followed by the conversion of this energy into heat is a fundamental plasma physics process. A theoretical foundation for the study of this process is constructed, but the details of the kinetic cascade are not well understood. Several important properties are identified: (a) the conservation of a generalized energy by the cascade; (b) the need for collisions to increase entropy and realize irreversible plasma heating; and (c) the key role played by the entropy cascade--a dual cascade of energy to small scales in both physical and velocity space--to convert ultimately the turbulent energy into heat. A strategy for nonlinear numerical simulations of kinetic turbulence is outlined. Initial numerical results are consistent with the operation of the entropy cascade. Inertial range turbulence arises in a broad range of space and astrophysical plasmas and may play an important role in the thermalization of fusion energy in burning plasmas.