Slow down of a globally neutral relativistic $e^-e^+$ beam shearing the vacuum

TL;DR

This study uses multidimensional PIC simulations to show that a relativistic electron-positron beam shearing through a hollow channel excites the Mushroom instability, converting kinetic energy into electromagnetic fields and slowing the beam.

Contribution

It demonstrates the excitation of the Mushroom instability in a globally neutral relativistic beam without contact with channel walls, revealing a new collisionless shear physics mechanism.

Findings

Mushroom instability is excited in relativistic $e^-e^+$ beams shearing through hollow channels.

The instability converts kinetic energy into magnetic and electric fields.

The process can slow down the beam without physical contact, relevant to astrophysical environments.

Abstract

The microphysics of relativistic collisionless sheared flows is investigated in a configuration consisting of a globally neutral, relativistic $e^-e^+$ beam streaming through a hollow plasma/dielectric channel. We show through multidimensional PIC simulations that this scenario excites the Mushroom instability (MI), a transverse shear instability on the electron-scale, when there is no overlap (no contact) between the $e^-e^+$ beam and the walls of the hollow plasma channel. The onset of the MI leads to the conversion of the beam's kinetic energy into magnetic (and electric) field energy, effectively slowing down a globally neutral body in the absence of contact. The collisionless shear physics explored in this configuration may operate in astrophysical environments, particularly in highly relativistic and supersonic settings where macroscopic shear processes are stable.