All-optical density downramp injection in electron-driven plasma wakefield accelerators

TL;DR

This paper demonstrates a novel all-optical method for controlled electron injection in plasma wakefield accelerators using laser-induced plasma density spikes, enabling high-quality, customizable electron beams.

Contribution

First experimental demonstration of laser-controlled plasma density downramp injection in an electron-driven plasma wakefield accelerator.

Findings

Controlled injection of high-quality electron beams achieved.

Laser pulses create tunable plasma density spikes for injection.

Produced unique beam configurations like counter-oscillating twin beamlets.

Abstract

Injection of well-defined, high-quality electron populations into plasma waves is a key challenge of plasma wakefield accelerators. Here, we report on the first experimental demonstration of plasma density downramp injection in an electron-driven plasma wakefield accelerator, which can be controlled and tuned in all-optical fashion by mJ-level laser pulses. The laser pulse is directed across the path of the plasma wave before its arrival, where it generates a local plasma density spike in addition to the background plasma by tunnelling ionization of a high ionization threshold gas component. This density spike distorts the plasma wave during the density downramp, causing plasma electrons to be injected into the plasma wave. By tuning the laser pulse energy and shape, highly flexible plasma density spike profiles can be designed, enabling dark current free, versatile production of high-quality electron beams. This in turn permits creation of unique injected beam configurations such as counter-oscillating twin beamlets.