Evidence of new finite beam plasma instability for magnetic field generation

TL;DR

This paper presents evidence from simulations, experiments, and theory for a new finite beam plasma instability that generates magnetic fields at large scales, challenging previous assumptions based on infinite systems.

Contribution

It introduces a previously unknown instability in finite beam plasma systems responsible for large-scale magnetic field generation, supported by multiple methods.

Findings

Discovery of a new finite beam plasma instability

Magnetic fields generated at scales larger than electron skin depth

Finite boundaries cause radiative leakage absent in infinite models

Abstract

We demonstrate by computer simulations, laser plasma experiments, and analytic theory that a hitherto unknown instability is excited in the beam plasma system with finite transverse size. This instability is responsible for the generation of magnetic fields at scales comparable to the transverse beam dimension which can be much longer than the electron skin depth scale. This counterintuitive result arises due to radiative leakage associated with finite beam boundaries which are absent in conventional infinite periodic systems considered in earlier simulations as well as theoretical analyses and may trigger a reexamination of a hitherto prevalent idea.