Detection of Wakefield using test-bunch method at photon factory advanced ring

Curious phenomena which depend on the beam current have been appeared during injection into PF-AR. In order to get information on the wake field, a test-bunch method has been carried out: a main bunch with a large current and a test bunch with a smaller current are stored and wake field excited by the main bunch is estimated from the motion of the test bunch. Experimental results and an analytical calculation suggest that the wake field excited in rf cavities influence the injection rate. The wake field estimated by the test bunch method is compared with the calculated field and the motions of the stored and injected beam are discussed.