Radiative diagnostics for sub-Larmor scale magnetic turbulence

TL;DR

This paper introduces a method to diagnose small-scale magnetic turbulence in high-energy density plasmas by analyzing radiation from particles, enabling insights into magnetic field properties in laser experiments, shocks, and reconnection.

Contribution

It develops a general jitter radiation framework to relate emitted radiation spectra to the spectral distribution of turbulent magnetic fields, providing a new diagnostic tool.

Findings

Radiation depends on the magnetic field spectral distribution.

The method applies to filamentation instability regions.

Spectral analysis can reveal magnetic turbulence characteristics.

Abstract

Radiative diagnostics of high-energy density plasmas is addressed in this paper. We propose that the radiation produced by energetic particles in small-scale magnetic field turbulence, which can occur in laser-plasma experiments, collisionless shocks, and during magnetic reconnection, can be used to deduce some properties of the turbulent magnetic field. Particles propagating through such turbulence encounter locally strong magnetic fields, but over lengths much shorter than a particle gyroradius. Consequently, the particle is accelerated but not deviated substantially from a straight line path. We develop the general jitter radiation solutions for this case and show that the resulting radiation is directly dependent upon the spectral distribution of the magnetic field through which the particle propagates. We demonstrate the power of this approach in considering the radiation produced by particles moving through a region in which a (Weibel-like) filamentation instability grows magnetic fields randomly oriented in a plane transverse to counterstreaming particle populations. We calculate the spectrum as would be seen from the original particle population and as could be seen by using a quasi-monoenergetic electron beam to probe the turbulent region at various angles to the filamentation axis.