Observation of beam loading in a laser-plasma accelerator

TL;DR

This paper presents an experimental study of beam loading in a laser-plasma accelerator, showing how increased beam charge affects energy, dark current, and energy spread, supported by 3D PIC simulations.

Contribution

It provides the first detailed experimental characterization of beam loading effects in laser-plasma accelerators, validated by simulations.

Findings

Beam loading causes energy decrease and increased energy spread.

Decelerating fields of about 1 GV/m/pC are generated.

Optimal beam loading occurs at around 20 pC charge.

Abstract

Beam loading is the phenomenon which limits the charge and the beam quality in plasma based accelerators. An experimental study conducted with a laser-plasma accelerator is presented. Beam loading manifests itself through the decrease of the beam energy, the reduction of dark current and the increase of the energy spread for large beam charge. 3D PIC simulations are compared to the experimental results and confirm the effects of beam loading. It is found that, in our experimental conditions, the trapped electron beams generate decelerating fields on the order of 1 GV/m/pC and that beam loading effects are optimized for trapped charges of about 20 pC.