CAS, Inst High Energy Phys, Beijing 100049, Peoples R China
; KEK, High Energy Accelerator Res Org, Tsukuba, Ibaraki 3050801, Japan
The medium-energy beam-transport line (MEBT) plays an important role in reducing the beam loss in the Japan Proton Accelerator Research Complex (J-PARC). A MEBT was designed and constructed, with good beam matching and lower beam loss. A brief introduction to the MEBT,and its beam test results are given. To further reduce the beam loss during the transient time of the chopper, a medium-energy beam-transport line with an anti-chopper has been designed. It accomplishes three tasks: matching the beam from the RFQ to the acceptance of the DTL, chopping the beam to produce gaps for injection into the rapid cycling ring which follows the linac, and returning the partially deflected beam back to the acceptance of the DTL. An RF chopper and an anti-chopper have been adopted in the beam line, and the optimization of the design of the chopper cavity is discussed. Details of the beam dynamics analysis are given.