Differential pumping for kHz operation of a laser wakefield accelerator based on a continuously flowing hydrogen gas jet.

Laser-Wakefield Accelerators (LWFAs) running at kHz repetition rates hold great potential for applications. They typically operate with low-energy, highly compressed laser pulses focused on high-pressure gas targets. Experiments have shown that the best-quality electron beams are achieved using hydrogen gas targets. However, continuous operation with hydrogen requires a dedicated pumping system. In this work, we present a method for designing a differential pumping system, which we successfully implemented in our experiments. This enabled the first demonstration of continuous operation of a kHz LWFA using a high-pressure hydrogen gas jet. The system effectively maintained a pressure below 3 × 10-4 mbar, even with a free-flowing gas jet operating at 140 bar backing pressure. Numerical fluid dynamics and optical simulations were used to guide and validate the system's design.