Development of a LWFA target for fine electron injection control

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Laser-plasma accelerators (LPAs) employ intense laser pulses focused into a gas target to drive plasma waves with electric fields strong enough to accelerate electrons to relativistic energies, offering accelerator facilities orders of magnitude more compact than conventional ones. Recent advances have demonstrated high-quality electron beams with up to 8 GeV energy gain [1], per- mille-level energy spread [2], 10–100 pC charge, few-femtosecond duration [3], sub-milliradian divergence, and repetition rates on the kilohertz range [4].

However, reproducibility remains a major limitation due to shot-to-shot fluctuations arising from laser instabilities, plasma density variations, and stochastic injection dynamics, hindering precision applications such as medical therapy [5] and LPA-driven X-FELs [6]. We present a novel two-chamber gas cell enabling precise, tunable control of the plasma density profile via independent temperature regulation, supporting reproducible, charge-tunable electron beam generation through a down-ramp injection scheme.

The adjustable cell length facilitates energy tuning and compatibility with diverse experimental setups. Computational Fluid Dynamics (CFD) simulations using OpenFOAM [7] confirm the feasibility of the designed density profiles, while Bayesian optimization applied to particle-in-cell simulations using OSIRIS [8] identifies optimal laser–plasma parameters. Experimental assembly and testing of the gas target, including the temperature and gas injection control system, are also reported.