Beam study on MEBT1 at the J-PARC LINEAC

Okabe, Kota  ; Liu, Y.*; Otani, Masashi*; Moriya, Katsuhiro  ; Miyao, Tomoaki*; Kitamura, Ryo   ; Hirano, Koichiro  ; Oguri, Hidetomo  ; Kinsho, Michikazu  

The J-PARC linac has a medium energy beamline (MEBT1) between RFQ and DTL. The MEBT1 is equipped with an RF beam chopper system to control the macro-bunch beam shape in the longitudinal direction so as to match the Circular Accelerator (RCS) in the latter stage. Two buncher cavities are installed in the existing MEBT1 for the matching the longitudinal shape of the beam with the chopper system and the downstream DTL. However, in principle, a total of three bunchers are required: one for the chopper system and two for beam shape matching with the DTL. Therefore, there have been long discussions about the design of the new MEBT1, which is an MEBT1 with a buncher added. On the other hand, in MEBT1, the space charge effect is very strong, and it is difficult to install beam monitors in the DTL section, so it is difficult to clarify the current experimental results using numerical simulations. We first conducted systematic beam experiments to investigate how the beam quality could be improved by adding a buncher to the MEBT1. As a result of examining the risks and benefits that would improve from remaking MEBT1 from the results of beam experiments, it was found that there was little merit in installing the new MEBT1 in terms of achieving a beam power of a little over 1 MW at the J-PARC accelerators. It was determined that the MEBT1 of 1 can be adequately handled. In this paper, we report the results of beam experiments on the MEBT1 and the review process of the new MEBT1.