Optimization and stabilization of a kilohertz laser-plasma accelerator

TL;DR

This paper systematically investigates kilohertz laser-plasma accelerators, demonstrating stable operation over millions of shots, analyzing different regimes, and explaining processes through simulations, advancing towards reliable high-repetition-rate electron beams.

Contribution

It provides a comprehensive study of pulse duration and plasma density effects, and demonstrates unprecedented stability in laser-plasma acceleration over millions of shots.

Findings

High-quality electron beams achieved with short pulses in moderate plasma densities.

Stable operation over 18 million shots with consistent beam parameters.

Micro-scale density gradient injection is key to stability.

Abstract

Laser plasma acceleration at kilohertz repetition rate has recently been shown to work in two different regimes, with pulse lengths of either 30 fs or 3.5 fs. We now report on a systematic study in which a large range of pulse durations and plasma densities were investigated through continuous tuning of the laser spectral bandwidth. Indeed, two LPA processes can be distinguished, where beams of the highest quality, with 5.4 pC charge and a spectrum peaked at 2-2.5 MeV are obtained with short pulses propagating in moderate plasma densities. Through Particle-in-Cell simulations the two different acceleration processes are thoroughly explained. Finally, we proceed to show the results of a 5-hour continuous and stable run of our LPA accelerator accumulating more than $\mathrm{18\times10^6}$ consecutive shots, with 2.6 pC charge and peaked 2.5 MeV spectrum. A parametric study of the influence of the laser driver energy through PIC simulations underlines that this unprecedented stability was obtained thanks to micro-scale density gradient injection. Together, these results represent an important step towards stable laser-plasma accelerated electron beams at kilohertz repetition rate.