Global spill control in RF-knockout slow-extraction

The time structure of extracted beams has been improved in synchrotron rings with resonant slow-extraction including RF-knockout extraction. In order to control the global spill structure in the RF-knockout slow-extraction method, it is necessary to improve the amplitude modulation (AM) function of the transverse RF-field. For this purpose, a scheme with a simple model of the extraction process has been proposed. Using this simple model, an analysis was carried out for determining the parameter relevant to the diffusion process in the separatrix. With this parameter, the new AM function obtained by the analytical approach could provide a flat spill within ±23% in both a simulation and an experiment at the HIMAC synchrotron. Cooperating with the feedback system, the global spill structure was significantly suppressed to be less than ±5%.