Electron bunch generation from a plasma photocathode

TL;DR

This paper demonstrates a novel plasma photocathode method for generating ultra-bright, low-emittance electron beams using laser-triggered ionization in a plasma, advancing compact accelerator technology.

Contribution

It introduces a new optical injection technique in plasma wakefield accelerators that produces high-quality electron beams with unprecedented brightness.

Findings

Successful optical injection and acceleration of electron bunches.

Generation of electron beams with ultra-low transverse emittance.

Potential for high-brightness beams for advanced applications.

Abstract

Plasma waves generated in the wake of intense, relativistic laser or particle beams can accelerate electron bunches to giga-electronvolt (GeV) energies in centimetre-scale distances. This allows the realization of compact accelerators having emerging applications, ranging from modern light sources such as the free-electron laser (FEL) to energy frontier lepton colliders. In a plasma wakefield accelerator, such multi-gigavolt-per-metre (GV m$^{-1}$) wakefields can accelerate witness electron bunches that are either externally injected or captured from the background plasma. Here we demonstrate optically triggered injection and acceleration of electron bunches, generated in a multi-component hydrogen and helium plasma employing a spatially aligned and synchronized laser pulse. This ''plasma photocathode'' decouples injection from wake excitation by liberating tunnel-ionized helium electrons directly inside the plasma cavity, where these cold electrons are then rapidly boosted to relativistic velocities. The injection regime can be accessed via optical density down-ramp injection, is highly tunable and paves the way to generation of electron beams with unprecedented low transverse emittance, high current and 6D-brightness. This experimental path opens numerous prospects for transformative plasma wakefield accelerator applications based on ultra-high brightness beams.