Magnetic field generation by an inhomogeneous return current

TL;DR

This paper introduces a novel mechanism for magnetic field generation in inhomogeneous collisionless plasmas with beam components, supported by simulations, with implications for cosmic magnetic fields originating from early cosmic rays.

Contribution

The study proposes a new magnetic field generation mechanism in inhomogeneous plasmas, demonstrated through particle-in-cell simulations, relevant to cosmic ray interactions in the early universe.

Findings

Magnetic fields can be generated in inhomogeneous plasmas despite initial neutrality.

Simulation results confirm the viability of the proposed mechanism.

Implications for large-scale cosmic magnetic fields from early cosmic rays.

Abstract

A new generation mechanism of the magnetic field in an inhomogeneous collisionless plasma with a beam component is proposed. We show that even though the current and charge neutralities are initially satisfied, the current neutrality is eventually violated if there is an inhomogeneity, so that the magnetic field is generated. By conducting ab initio two-dimensional particle-in-cell simulations, we demonstrate that the magnetic field is generated as expected. The new generation mechanism of the magnetic field can play an important role in the current universe because cosmic rays can be regarded as the beam component in the astrophysical plasma. We propose that the first cosmic rays generate the magnetic field with a large scale at the redshift of z ~ 20.