Ion dynamics driven by a strongly nonlinear plasma wake

TL;DR

This paper investigates ion behavior in plasma wakefield accelerators post-wave breaking, revealing complex ion dynamics and structures driven by nonlinear plasma interactions through numerical simulations.

Contribution

It provides a detailed numerical analysis of ion dynamics driven by nonlinear plasma wakefields, highlighting four key physical effects and their interplay.

Findings

Formation of ion density peaks near the axis.

Generation of ion-acoustic solitons after wave decay.

Radial ion acceleration and plasma pinching observed.

Abstract

In plasma wakefield accelerators, the wave excited in the plasma eventually breaks and leaves behind slowly changing fields and currents that perturb the ion density background. We study this process numerically using the example of a FACET experiment where the wave is excited by an electron bunch in the bubble regime in a radially bounded plasma. Four physical effects underlie the dynamics of ions: (1) attraction of ions toward the axis by the fields of the driver and the wave, resulting in formation of a density peak, (2) generation of ion-acoustic solitons following the decay of the density peak, (3) positive plasma charging after wave breaking, leading to acceleration of some ions in the radial direction, and (4) plasma pinching by the current generated during the wavebreaking. Interplay of these effects result in formation of various radial density profiles, which are difficult to produce in any other way