Beam-dynamics-informed determination of subharmonic buncher phase and amplitude in the High Energy Photon Source Linac

The High Energy Photon Source (HEPS) Linac is a normal-conducting electron linear accelerator capable of producing high bunch charge beam. Its bunching system includes two subharmonic bunchers (SHBs), one prebuncher, one buncher, and one accelerating structure. The SHB is commonly used in the low-energy section for longitudinal bunching to increase the bunch charge. The phase and voltage of the SHB are crucial for obtaining a high-quality electron beam in Linac. This paper presents a method for calibrating the phase and voltage of the SHB using the time-of-flight technique. Experiments were conducted at the HEPS Linac using two beam position monitors. According to the simulations, we found that bunch length and space charge effect have a significant impact on the results, and we propose corrective measures to address them. To enhance experimental efficiency, we propose a data processing method called the truncated averaging technique that eliminates the need for corrective measures, which has been validated through both simulations and experiments, yielding outstanding results. This paper presents detailed insights into both the simulation and experimental procedures.