Collision-dependent power law scalings in 2D gyrokinetic turbulence

TL;DR

This paper extends the scaling theory of 2D electrostatic gyrokinetic turbulence to include moderate collisionality, predicting non-universal power law scalings confirmed by numerical simulations.

Contribution

It generalizes existing weakly collisional cascade theory to the moderately collisional regime, revealing new non-universal scalings due to multiscale dissipation.

Findings

Predicted non-universal power law scalings in collisional regimes

Confirmed scalings through direct numerical simulations

Extended understanding of turbulence dissipation mechanisms

Abstract

Nonlinear gyrokinetics provides a suitable framework to describe short-wavelength turbulence in magnetized laboratory and astrophysical plasmas. In the electrostatic limit, this system is known to exhibit a free energy cascade towards small scales in (perpendicular) real and/or velocity space. The dissipation of free energy is always due to collisions (no matter how weak the collisionality), but may be spread out across a wide range of scales. Here, we focus on freely-decaying 2D electrostatic turbulence on sub-ion-gyroradius scales. An existing scaling theory for the turbulent cascade in the weakly collisional limit is generalized to the moderately collisional regime. In this context, non-universal power law scalings due to multiscale dissipation are predicted, and this prediction is confirmed by means of direct numerical simulations.