Wakefield decay in a radially bounded plasma due to formation of electron halo

TL;DR

This paper identifies a new damping mechanism for wakefields in bounded plasmas caused by electron halo formation, which can significantly limit wakefield lifetime in plasma-based acceleration.

Contribution

It introduces the electron halo effect as a novel damping process and emphasizes the importance of simulation window size for accurate modeling.

Findings

Electron halo formation leads to wakefield damping.

Halo electrons efficiently extract energy from the wave.

Proper simulation window size is crucial for accurate results.

Abstract

There is a new effect that can limit the lifetime of a weakly nonlinear wakefield in a radially bounded plasma. If the drive beam is narrow, some of the plasma electrons fall out of the collective motion and leave the plasma radially, forming a negatively charged halo around it. These electrons repeatedly return to the plasma under the action of the charge separation field, interact with the plasma wave and cause its damping. The lowest-energy halo electrons take the energy from the wave more efficiently, because their trajectories are bent by the plasma wave towards the regions of the strongest acceleration. For correct accounting of the wave damping in simulations, it is necessary and sufficient to take the simulation window twice as wide as the plasma.