Elsa Baynard

The present article reports on the generation of stable 50 pC low-divergence electron beams above 150 MeV from laser-driven wakefield acceleration using a continuous-flow gas target prototype tested at the 60 TW Salle Jaune facility at LOA. The gas target design is meant to be easily transported and integrated as an element of the beamline with a differential pumping system offering some 10⁻⁴ mbar pressure in the rest of the line. A dedicated gas injection system allows for the control of the gas mixture concentration and gas pressure in two different regions of the target within the frame of controlled ionisation injection schemes. The measured electron beam parameters show the importance of gas density profiles and longitudinal gas mixture confinement.

Exploring novel target schemes for laser wakefield accelerators is essential to address the challenge of increasing repetition rates while ensuring the stability and quality of the produced electron beams. This paper introduces and discusses the prototyping of a two-chamber gas target, integrated into the beamline and operating under continuous gas flow, in the framework of ionization injection. We present the numerical fluid modeling employed to assist the density profile shaping, with a focus on gas mixing and dopant confinement. The importance of localized high-Z gas for ionization injection is demonstrated through particle-in-cell simulations using the simulated gas profiles. We describe the test bench used for prototype evaluation, specifically addressing the plasma electron density and the longitudinal distribution of species relevant to ionization injection. The lifetime of the target at 10 Hz and 60 mJ is measured for different materials, and its effect on the resulting electron beam is assessed using particle-in-cell simulations. Finally, we outline perspectives on high-power operation.