Radiation damage and lifetime estimation of the proton beam window at the Japan Spallation Neutron Source

The proton beam window (PBW) is a component that separates the high-vacuum area of the accelerator from the target area in the Japan Proton Accelerator Research Complex's Japan Spallation Neutron Source USNS). It is important to estimate the damage accumulated from proton beam irradiation to establish a safe lifetime for the window. The PBW is made of an aluminum alloy, which was chosen because of its successful use in the target safety hull of the Swiss Spallation Neutron Source (SINQ). Post-irradiation examination (PIE) performed on SINQ Target 3 after irradiation with a 0.6 GeV proton beam measured the gas production in its aluminum safety hull. To estimate a safe lifetime for the JSNS PBW, we calculated the displacement per atom (DPA) and gas production rate using the Particle and Heavy Ion Transport code System (PHITS) for 0.6- and 3-GeV protons. For the hydrogen gas production rate, PHITS shows good agreement with the SINQ PIE results; however, for the helium production rate, it predicts a 45% lower value than the experimental result of 1125 appm. The calculated result for helium production was normalized to fit the experimental results of SINQ. We conservatively estimate the lifetime of the JSNS PBW using the condition that the hydrogen production rate does not exceed the value measured at SINQ. The lifetime of the PBW corresponds to a proton beam fluence of 1.8 x 10(21) cm(-2), which is equivalent to an integrated beam power of 8000 MW h with the designed current density of 10 mu A cm(-2). The peak density will be reduced to 8.4 mu A cm(-2) to suppress cavitation pitting damage in the mercury target vessel. Consequently, the lifetime of the PBW will be 9500 MW h. (C) 2014 Elsevier B.V. All rights reserved.