Cumulative effect of Weibel-type instabilities in counterstreaming plasmas with non-Maxwellian anisotropies

TL;DR

This paper investigates how Weibel-type instabilities grow in counterstreaming plasmas with non-Maxwellian anisotropies, revealing enhanced magnetic field generation potential relevant for astrophysical and laboratory plasmas.

Contribution

It generalizes the analysis of filamentation and Weibel instabilities to bi-kappa distributions, showing how non-Maxwellian features influence instability growth rates.

Findings

Bi-kappa distributions can significantly increase filamentation instability growth rates.

Hotter plasma in the streaming direction enhances the Weibel instability.

Results support the role of Weibel instabilities in rapid plasma magnetization.

Abstract

Counterstreaming plasma structures are widely present in laboratory experiments and astrophysical systems, and they are investigated either to prevent unstable modes arising in beam-plasma experiments or to prove the existence of large scale magnetic fields in astrophysical objects. Filamentation instability arises in a counterstreaming plasma and is responsible for the magnetization of the plasma. Filamentationally unstable mode is described by assuming that each of the counterstreaming plasmas has an isotropic Lorentzian (kappa) distribution. In this case, the filamentation instability growth rate can reach a maximum value markedly larger than that for a a plasma with a Maxwellian distribution function. This behaviour is opposite to what was observed for the Weibel instability growth rate in a bi-kappa plasma, which is always smaller than that obtained for a bi-Maxwellian plasma. The approach is further generalized for a counterstreaming plasma with a bi-kappa temperature anisotropy. In this case, the filamentation instability growth rate is enhanced by the Weibel effect when the plasma is hotter in the streaming direction, and the growth rate becomes even larger. These effects improve significantly the efficiency of the magnetic field generation, and provide further support for the potential role of the Weibel-type instabilities in the fast magnetization scenarios.