Theory of the Jitter radiation in a magnetized plasma accompanying temperature gradient

TL;DR

This paper reexamines the stability of magnetized plasma with temperature gradients, deriving jitter radiation spectra emitted by relativistic electrons, and finds that plasma instabilities produce nearly unpolarized circularly polarized waves.

Contribution

It introduces the first derivation of jitter radiation spectra in magnetized plasma with temperature gradient-driven instabilities, linking plasma physics with radiation emission.

Findings

Plasma instability driven by temperature gradients excites circularly polarized magnetic waves.

Jitter radiation is emitted alongside synchrotron radiation from relativistic electrons.

The polarization degree of jitter radiation is very small due to balanced wave excitation.

Abstract

The linear stability of a magnetized plasma accompanying temperature gradient was reexamined by using plasma kinetic theory. The anisotropic velocity distribution function was decomposed into two components. One is proportional to the temperature gradient parallel to and the other is proportional to the temperature gradient perpendicular to the back ground magnetic field. Since the amplitude of the anisotropic velocity distribution function is proportional to the heat conductivity and the heat conductivities perpendicular to the magnetic field is strongly reduced, the first component of the anisotropic velocity distribution function is predominant. The anisotropic velocity distribution function induced by the temperature gradient along the back ground magnetic field drives plasma kinetic instability and the circular polarized magnetic plasma waves are excited. The instability is almost identical to Weibel instability in weakly magnetized plasma. However, depending on whether wave vectors of modes are parallel to or antiparallel to the back ground magnetic field, the growth rate is suppressed or enhanced due to back ground magnetic field. In the strongly magnetized plasma, one mode is stabilized and only one of the modes remains unstable. The Jitter radiation spectrum formulae emitted by relativistic electrons when they travel through the magnetized plasma with the plasma waves driven by the instability, are deduced at the first time. The synchrotron emission and the Jitter radiation are simultaneously emitted from the same relativistic electron. The Jitter radiation is expected to be circularly polarized but with a very small polarization degree since almost the same amount of left and right handed circular polarized magnetic waves are excited by the instability.