• K. Yoshimura, Y. Hashimoto, Y. Hori, Y. Igarashi, S. Mihara, H. Nishiguchi, Y. Sato, M. Shimamoto, Y. Takeda, M. Uota
  KEK, Ibaraki
• M. Aoki, N. Nakadozono, T. Tachimoto
  Osaka University, Osaka

Pro­ton beam ex­tinc­tion, de­fined as a resid­u­al to pri­ma­ry ratio of beam in­ten­si­ty, is one of the most im­por­tant pa­ram­e­ters to re­al­ize the fu­ture muon elec­tron con­ver­sion ex­per­i­ment (COMET) pro­posed at J-PARC. To achieve the re­quired ex­tinc­tion level of 10^-9, we start­ed mea­sur­ing beam ex­tinc­tion at main ring (MR) as the first step. The newly de­vel­oped beam mon­i­tor was in­stalled into the abort beam line and the first mea­sure­ment was suc­cess­ful­ly per­formed by using the fast-ex­tract­ed MR beam. We found that empty RF buck­ets of RCS, in which all pro­tons were con­sid­ered to be swept away by a RF chop­per be­fore in­jec­tion to RCS,, con­tained about 10^-5 of the main beam pulse due to chop­per in­ef­fi­cien­cy. We are now de­vel­op­ing a new beam mon­i­tor with im­proved per­for­mance for fur­ther stud­ies at the abort line. In ad­di­tion, we have start­ed new mea­sure­ments at the dif­fer­ent stage of pro­ton ac­cel­er­a­tion, i.e. at Linac, 3-50 BT line, and the main ring. In this paper, we pre­sent re­cent re­sults and fu­ture prospect of beam ex­tinc­tion mea­sure­ments.