Stability of ionisation-injection-based laser-plasma accelerators

TL;DR

This study demonstrates the stable operation of ionisation-injection laser-plasma accelerators over 8 hours, analyzing shot-to-shot variations and the influence of plasma density fluctuations on beam quality and stability.

Contribution

It provides the first long-duration stability analysis of ionisation-injection LPA, linking plasma density fluctuations to beam charge jitter and emittance variations.

Findings

Beam charge remained stable over 8 hours with minimal drift.

Shot-to-shot charge jitter was 26%, correlated with plasma density fluctuations.

Simulations showed self-focusing effects increase charge and emittance at higher densities.

Abstract

Laser-plasma acceleration (LPA) is a compact technique to accelerate electron bunches to highly relativistic energies, making it a promising candidate to power radiation sources for industrial or medical applications. We report on the generation of electron beams from an 80 MeV-level LPA setup based on ionisation injection (II) over a duration of 8 hours at a repetition rate of 2.5 Hz, resulting in 72,000 consecutive shots with charge injection and acceleration. Over the full operation time the moving averages of the total beam charge of 14.5 pC and the charge between 70-80 MeV did not drift on a detectable level. The largest source of shot-to-shot jitter was in the beam charge (26% standard deviation), which was most strongly correlated with fluctuations in the plasma density (3.6% standard deviation). Particle-in-cell simulations demonstrate that this was chiefly caused by stronger laser self-focusing in higher density plasmas, which significantly increased the ionised charge along with the emittance of the beam. The nonlinearity of this process imposes tight constraints on the reproducibility of the laser-plasma conditions required for a low jitter II-LPA output if self-focusing plays a role in the laser evolution.