Guided mode evolution and ionization injection in meter-scale multi-GeV laser wakefield accelerators

TL;DR

This paper demonstrates a new nonlinear propagation regime in meter-scale laser wakefield accelerators, where mode beating influences ionization injection and results in multi-GeV electron energy spectra with high monoenergeticity.

Contribution

It introduces a 3-stage model explaining mode beating effects and ionization injection in low-density plasma waveguides, advancing understanding of electron acceleration mechanisms.

Findings

Mode beating leads to ionization injection and multi-GeV peaks.

Single multi-GeV peaks with <10% energy spread achieved.

Experimental results explained by a new 3-stage model.

Abstract

We show that laser wakefield electron accelerators in meter-scale, low density hydrodynamic plasma waveguides operate in a new nonlinear propagation regime where sustained beating of lowest order modes of the ponderomotively modified channel plays a significant role, whether or not the injected pulse is linearly matched to the guide. For a continuously doped gas jet, this mode beating effect leads to ionization injection and a striated multi-GeV energy spectrum of multiple quasi-monoenergetic peaks; the same process in a locally doped jet produces single multi-GeV peaks with <10% energy spread. A 3-stage model of drive laser pulse evolution and ionization injection characterizes the beating effect and explains our experimental results.