Study of the beam loss localization in the J-PARC RCS

Kojima, Kunihiro ; Harada, Hiroyuki  ; Saha, P. K.   

Uncontrolled beam loss in the 3 GeV rapid-cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) was investigated. A significant amount of uncontrolled beam loss was observed, especially at each arc section, despite the RCS being equipped with a collimation system designed to collect halo particles with one scatterer and five absorbers. Based on the time-dependence of the beam loss measured in the collimation system and arc sections, the particles lost at the arc sections are found to be likely scattered by the absorber rather than the scatterer, contrary to the design of the collimation system. By changing the configuration of the collimation system, it was determined that the absorber through which the majority of the lost particles passed was the second absorber. In addition, the trajectory of such a particle was identified by using numerical simulation assuming the lattice structure of the RCS.