Characterization of the equilibrium configuration for modulated beams in a plasma wakefield accelerator

TL;DR

This paper investigates the equilibrium states of modulated beams in plasma wakefield accelerators, identifying multiple configurations and analyzing their evolution and stability during propagation.

Contribution

It introduces a semi-analytical method to characterize equilibrium configurations and examines their dynamic behavior in plasma, highlighting the backward drift phenomenon.

Findings

Multiple equilibrium configurations exist for modulated beams.

The most suitable configuration for wakefield excitation is identified.

Equilibrium configurations exhibit a backward drift during propagation.

Abstract

We analyze the equilibrium configuration for a modulated beam with sharp boundaries exposed to the fields self-generated by the interaction with a plasma. Through a semi-analytical approach we show the presence of multiple equilibrium configurations and we determine the one more suitable for wakefield excitation. Once pointed out the absence of confinement for the front of the beam and the consequently divergence driven by the emittance, we study the evolution of the equilibrium configuration while propagating in the plasma, discarding all the others time-dependencies. We show the onset of a rigid backward drift of the equilibrium configuration and we provide an explanation in the increasing length of the first bunch.