Nonlinear phase mixing and phase-space cascade of entropy in gyrokinetic plasma turbulence

TL;DR

This paper investigates how entropy cascades in phase space drive energy dissipation in gyrokinetic plasma turbulence, revealing a universal kinetic turbulence regime with implications for turbulent heating.

Contribution

It demonstrates the existence of a universal entropy cascade in phase space with specific spectral scalings, advancing understanding of energy dissipation in plasma turbulence.

Findings

Identification of a broad spectrum of sub-Larmor scale fluctuations.

Theoretical predictions of fluctuation scalings in velocity and position space.

Turbulent heating rate increases with fluctuation amplitude, independent of collision frequency.

Abstract

Electrostatic turbulence in weakly collisional, magnetized plasma can be interpreted as a cascade of entropy in phase space, which is proposed as a universal mechanism for dissipation of energy in magnetized plasma turbulence. When the nonlinear decorrelation time at the scale of the thermal Larmor radius is shorter than the collision time, a broad spectrum of fluctuations at sub-Larmor scales is numerically found in velocity and position space, with theoretically predicted scalings. The results are important because they identify what is probably a universal Kolmogorov-like regime for kinetic turbulence; and because any physical process that produces fluctuations of the gyrophase-independent part of the distribution function may, via the entropy cascade, result in turbulent heating at a rate that increases with the fluctuation amplitude, but is independent of the collision frequency.