Whistler instability in a semi-relativistic bi-Maxwellian plasma

TL;DR

This paper analyzes the Weibel instability in semi-relativistic bi-Maxwellian plasmas using the Vlasov-Maxwell system, revealing how relativistic effects and ambient magnetic fields influence instability thresholds and growth rates in astrophysical environments.

Contribution

It provides analytical dispersion relations and growth rate estimates for the Weibel instability considering semi-relativistic effects and ambient magnetic fields, extending understanding in relativistic plasma scenarios.

Findings

Relativistic effects suppress the instability and lower the threshold.

Ambient magnetic fields reduce growth rates in non-resonant cases.

Growth rates are also characterized for field-free semi-relativistic plasmas.

Abstract

Employing linearized Vlasov-Maxwell system, the Weibel instability embedded in an ambient magnetic field is discussed for a semi-relativistic bi-Maxwellian distribution hoping such a scenario occurs in some relativistic environments e.g., gamma-ray burst sources and relativistic jet sources, supernovae, and galactic cosmic rays where the perpendicular temperature is much dominated over the parallel . The dispersion relations are analyzed analytically along with the graphical representation and the estimates of the growth rate are presented along with the instability threshold condition in the limiting cases i.e., xi<=1 (resonant case) and xi>>1 (non-resonant case). It is observed that the relativistic effect suppresses the instability and also lowers the threshold for the instability to set in. The ambient magnetic field contribution to instability appears only in non-resonant case resulting in reduction of growth rate. However, the effect of the ambient magnetic field is diminished as we go from the weak relativistic regime to the highly relativistic one. We also note that the ambient magnetic field generates real oscillations and the reletivistic effect reduces these oscillations. Further for field free case i.e., B0=0, the growth rates for Weibel instabilities are also presented in a semi-relativistic bi- Maxwellian plasma for both the limiting cases.