RF breakdown and dark current studies in short-pulse acceleration

Recent experimental studies at the Argonne Wakefield Accelerator (AWA) have shown that operating RF cavities with short pulses, only a few nanoseconds in duration, can raise the accelerating gradient to nearly 400 MV/m in a series of X-band structure tests. These results motivate further investigation into the breakdown physics underlying the short-pulse acceleration regime. In this work, we present analytical models and numerical simulations of dark current dynamics in X-band cavities driven by short RF pulses. These studies explore key phenomena associated with RF breakdown across various time scales, including field emission, secondary electron emission, and plasma formation, with particular focus on their dependence on RF pulse length. Building on these insights, we describe the design and experimental plan for a single-cell X-band RF cavity operating at 11.7 GHz, optimized for high-gradient operation with 6~ns long RF pulses and integrated with RF breakdown diagnostics. This work aims to deepen the understanding of RF breakdown physics in the short-pulse regime and support the development of compact linear accelerators for future applications.