Streaming cold cosmic ray back-reaction and thermal instabilities across the background magnetic field

TL;DR

This paper analyzes how streaming cosmic rays influence plasma instabilities in astrophysical environments, deriving a dispersion relation that links cosmic ray and plasma parameters to different thermal instability types.

Contribution

It introduces a multi-fluid model accounting for cosmic ray back-reaction on streaming and thermal instabilities, providing a new dispersion relation incorporating cosmic ray effects.

Findings

Cosmic rays induce streaming instability in plasma.

Thermal instability is unaffected by cosmic rays in this model.

Derived dispersion relation links sound velocities, Alfvén speed, and cosmic ray drift to instability types.

Abstract

Using the multi-fluid approach, we investigate streaming and thermal instabilities of the electron-ion plasma with homogeneous cold cosmic rays drifting perpendicular to the background magnetic field. Perturbations across the magnetic field are considered. The back-reaction of cosmic rays resulting in the streaming instability is taken into account. The thermal instability is shown not to be subject to the action of cosmic rays in the model under consideration. The dispersion relation for the thermal instability has been derived which includes sound velocities of plasma and cosmic rays, Alfv\'{e}n and cosmic ray drift velocities. The relation between these parameters determines the kind of thermal instability from Parker's to Field's type instability. The results obtained can be useful for a more detailed the investigation of electron-ion astrophysical objects such as galaxy clusters including the dynamics of streaming cosmic rays.