A compact energy-recovery linac (cERL) has been under development at KEK to drive key accelerator technologies, demonstrate energy recovery under various conditions, and support beam applications. cERL began beam operations in 2013 to create stable, low-emittance, energy-recovered beams. The project focused on gradually increasing the current transported in a stepwise fashion while maintaining low beam losses at each step. However, the energy recovery of high-current beams is an issue that needs to be addressed. In this study, we propose a method for high-current beam tuning of approximately 1 mA under energy-recovery conditions with extremely small beam loss. We prepared a collimator and a local fast beam loss monitor to reduce the beam loss. We report successful results at approximately 1 mA, demonstrating 100.0% energy recovery with extremely small beam loss. The radiofrequency (rf) amplitude and phase varied by less than 0.02% and 0.02°, respectively. The study findings are expected to provide insights into steady beam operation for high-brightness beams and high-efficiency energy-recovery operations required for future extreme ultraviolet free-electron lasers.
Sakai et al. (Fri,) studied this question.