Fabrication and cold test of photonic ba

This study presents a detailed description of the design and cold testing of photonic band gap (PBG) resonators and traveling-wave accelerator structures, which were essential for the subsequent hot test demonstration of the first PBG accelerator structure at 17.140 GHz. The PBG resonators were specifically designed to support only the main TM01-like accelerator mode, effectively avoiding the confinement of higher-order modes (HOM) or wakefields. A triangular lattice of rods with a missing central rod was employed for designing the PBG resonators, with a controlled rod radius-to-spacing ratio to enhance performance. The cold tests conducted at X-band (11 GHz) and Ku-band (17.140 GHz) yielded results that closely matched theoretical predictions, demonstrating excellent HOM suppression and a high Q factor. Additionally, the six-cell copper PBG accelerator traveling-wave structure showed significant reductions in long-range wakefields and was successfully tuned via rod etching. The promising outcomes of the cold tests laid the groundwork for the later hot testing of the structure, which confirmed the acceleration of the electron beam, thereby validating the design's efficacy.