Life cycle of the proton beam window in J-PARC MLF

Oi, Motoki ; Yamaguchi, Yuji   ; Kinoshita, Hidetaka   ; Meigo, Shinichiro   ; Haga, Katsuhiro  

Material and Life science experimental facility (MLF) in J-PARC is a spallation neutron source which uses 3 GeV proton beam with 1 MW power. The neutron production target is made with mercury and the target vessel is installed in the helium vessel. On the other hands, proton beam transport line is kept in high vacuum, less than 10 Pa to reduce the beam loss. As a boundary of the helium atmosphere and the vacuum region, proton beam window (PBW) is installed. The proton beam window is made with aluminum alloy. Due to the radiation damage of the window, lifetime of the PBW is estimated 10000 MWh. In this summer maintenance period, we replace from the PBW No. 4 to PBW No. 5. In this presentation, we report about life cycle, the structure and replacement work of the PBW.