Turbulence in Magnetized Pair Plasmas

TL;DR

This paper investigates Alfvénic turbulence in strongly magnetized pair plasmas, deriving equations across fluid and kinetic scales, predicting spectral slopes, and identifying a transition to tearing-mediated regimes.

Contribution

It derives coupled evolution equations for magnetic and flow potentials in pair plasmas, covering fluid and kinetic scales, and predicts spectral behaviors and transition scales.

Findings

Turbulence at fluid scales is similar to electron-ion plasmas, exhibiting critical balance and dynamic alignment.

A transition to a tearing-mediated regime occurs at a specific critical scale, with a predicted spectral slope of $k_ot^{-8/3}$ or $k_ot^{-3}.

Below the electron skin depth, turbulence is governed by inertial Alfvén waves, leading to a magnetic energy spectrum $mod k_ot^{-11/3}$.

Abstract

Alfv\'enic-type turbulence in strongly magnetized, low-beta pair plasmas is investigated. A coupled set of equations for the evolution of the magnetic and flow potentials are derived, covering both fluid and kinetic scales. In the fluid (MHD) range those equations are the same as for electron-ion plasmas, so turbulence at those scales is expected to be of the Alfv\'enic nature, exhibiting critical balance, dynamic alignment, and transition to a tearing mediated regime at small scales. The critical scale at which a transition to a tearing-mediated range occurs is derived, and the spectral slope in that range is predicted to be $k_\perp^{-8/3}$ (or $k_\perp^{-3}$, depending on details of the reconnecting configuration assumed). At scales below the electron (and positron) skin depth, it is argued that turbulence is dictated by a cascade of the inertial Alfv\'en wave, which we show to result in the magnetic energy spectrum $\propto k_\perp^{-11/3}$.