Magnetic field amplification by a nonlinear electron streaming instability

TL;DR

This paper introduces a new nonlinear instability in relativistic electron beams that significantly amplifies magnetic fields, with potential implications for astrophysics and laboratory plasma experiments.

Contribution

It identifies and analyzes a secondary nonlinear instability that enhances magnetic field amplification beyond linear predictions in relativistic electron streaming.

Findings

The instability can amplify magnetic fields by orders of magnitude.

It leads to large-scale plasma cavities with strong magnetic fields.

The analytical predictions agree with kinetic simulation results.

Abstract

Magnetic field amplification by relativistic streaming plasma instabilities is central to a wide variety of high-energy astrophysical environments as well as to laboratory scenarios associated with intense lasers and electron beams. We report on a new secondary nonlinear instability which arises for relativistic dilute electron beams after the saturation of the linear Weibel instability. This instability grows due to the transverse magnetic pressure associated with the beam current filaments, which cannot be quickly neutralized due to the inertia of background ions. We show that it can amplify the magnetic field strength and spatial scale by orders of magnitude, leading to large-scale plasma cavities with strong magnetic field and to very efficient conversion of the beam kinetic energy into magnetic energy. The instability growth rate, saturation level, and scale length are derived analytically and shown to be in good agreement with fully-kinetic simulations.