Stream instabilities in relativistically hot plasma

TL;DR

This paper analyzes the instabilities of relativistic ion beams in hot electron plasmas, identifying the Weibel instability as the fastest growing mode and exploring the growth of oblique modes, with implications for filament formation.

Contribution

It derives the growth rates of beam instabilities in relativistically hot plasmas for all propagation angles, highlighting the dominance of the Weibel instability and the role of oblique modes.

Findings

Weibel instability is the fastest growing mode in perpendicular direction.

Oblique modes grow nearly as fast and can distort filaments.

Filament structures observed in simulations are consistent with the instability analysis.

Abstract

The instabilities of relativistic ion beams in a relativistically hot electron background are derived for general propagation angles. It is shown that the Weibel instability in the direction perpendicular to the streaming direction is the fastest growing mode, and probably the first to appear, consistent with the aligned filaments that are seen in PIC simulations. Oblique, quasiperpendicular modes grow almost as fast, as the growth rate varies only moderately with angle, and they may distort or corrugate the filaments after the perpendicular mode saturates.