Ultra-high-gain water-window X-ray laser driven by plasma photocathode wakefield acceleration

TL;DR

This paper demonstrates through simulations how plasma wakefield accelerators can produce ultra-bright, tunable, femtosecond X-ray laser pulses in the water window, enabling compact and robust soft X-ray sources.

Contribution

It introduces a novel approach to generate high-gain, tunable water-window X-ray lasers using plasma photocathode wakefield acceleration, improving compactness and stability.

Findings

Achieved millijoule-gigawatt-class X-ray pulses

Demonstrated wavelength tunability via beam charge adjustment

Showed robustness against plasma wakefield variations

Abstract

X-ray free-electron lasers are large and complex machines, limited by electron beam brightness. Here we show through start-to-end simulations how to realise compact, robust and tunable X-ray lasers in the water window, based on ultra-bright electron beams from plasma wakefield accelerators. First, an ultra-low-emittance electron beam is released by a plasma photocathode in a metre-scale plasma wakefield accelerator. By tuning the beam charge, space-charge forces create a balance between beam fields and wakefields that reduces beam energy spread and improves energy stability - both critical for beam extraction, transport, and focusing into a metre-scale undulator. Here, the resulting ultra-bright beams produce wavelength-tunable, coherent, femtosecond scale photon pulses at ultra-high gain. This regime enables reliable generation of millijoule-gigawatt-class X-ray laser pulses across the water window, offering tunability via the witness beam charge and robustness against variations in plasma wakefield strength. Our findings help democratise access to coherent, high-power, soft X-ray radiation.