The self-injection threshold in self-guided laser wakefield accelerators

TL;DR

This paper investigates the conditions under which laser wakefield accelerators self-inject electrons, extending a theoretical model to account for variable bubble size and validating it with experimental data.

Contribution

It introduces an extended theoretical model for the self-injection threshold that considers self-focusing and pulse compression effects, aligning well with experimental results.

Findings

Extended the self-injection threshold model to include variable bubble size.

Experimental validation shows good agreement with the extended model.

Identified key parameters influencing self-injection in laser wakefield accelerators.

Abstract

A laser pulse traveling through a plasma can excite large amplitude plasma waves that can be used to accelerate relativistic electron beams in a very short distance---a technique called laser wakefield acceleration. Many wakefield acceleration experiments rely on the process of wavebreaking, or self-injection, to inject electrons into the wave, while other injection techniques rely on operation without self-injection. We present an experimental study into the parameters, including the pulse energy, focal spot quality and pulse power, that determine whether or not a wakefield accelerator will self-inject. By taking into account the processes of self-focusing and pulse compression we are able to extend a previously described theoretical model, where the minimum bubble size required for trapping is not constant but varies slowly with density and find excellent agreement with this model.