Radiation Damage in Aluminum Proton Beam Windows for SNS

Calculations of radiation damage are described for an aluminum-6061 proton-beam entrance window to the target station at the SNS, employing a 2-mA current of 1-GeV protons. The entrance window consists of two contoured plates of Al6061 separated by a cooling water gap. The incident proton current density at the center of the window is 0.28 A/m2. The neutron flux at the window is calculated using MCNPX. The neutron displacement cross sections stem from three types of calculations depending on neutron energy: (A) Below 20 MeV, SPECTER code; (B) 20 to 150 MeV, LA-150 calculations; and (C) Above 150 MeV, LAHET code. The total neutron-produced displacement rate is calculated to be 0.42 dpa/full-power year, with contributions of type (A), (B), and (C) of 73, 25, and 2%, respectively. The proton-produced displacement rate due to the incident 1-GeV protons is calculated to be 3.7 dpa/full-power year, thus giving a total displacement rate of 4.2 dpa/full-power year or 2.4 dpa/5000-hr operating year. The production rates for He and H are calculated to be about 300 appm He/dpa and 900 appm H/dpa. The significance of radiation damage is discussed with regard to the lifetime of the entrance window. (authors)