Optimized design of the thermionic cathode injector for the 1.0 GeV linear accelerator at the WALS

Abstract

Thermionic cathode injection systems are widely adopted for commissioning advanced light sources and linear accelerators due to their high bunch charge and operational reliability, and this robustness also makes them the preferred choice for high-dose irradiation accelerators. The 1.0 GeV linear accelerator at Wuhan University adopts a dual-injector scheme, where the thermionic cathode injector must satisfy compatibility with the photocathode injector beamline and adhere to the spatial constraints of the laboratory corridor, necessitating a compact layout design. This paper focuses on the optimized design of the tapered buncher, which is commonly integrated with thermionic cathode gun to deliver stable and high-quality electron beams, with phase velocity design as the primary optimization objective​​. Two design methodologies, numerical optimization and particle tracking optimization, were applied to determine the structural parameters of the buncher. Start-to-end optimization of the beamline incorporating space charge effects was performed by using the General Particle Tracer software, achieving matching between the injector exit beam and the main accelerator. Optimization calculations were further conducted for different injected charge levels, all yielding a transmission efficiency exceeding 60%.