Life time of carbon stripping foils for the Spallation Neutron Source

SNS requires thick carbon stripping foils (200 to 400 μg/cm² thick) to minimize the injection loss due to H⁰ emerging from the foil and the circulating beam loss due to Coulomb and nuclear scattering on the foil. Lifetimes of different types thick carbon foils had been measured in BNL Linac, using a 750 keV 6.7 Hz H^- beam. Beam current (~2 mA over a beam pulse) was selected such that the energy deposition on the foil would be equivalent to that by the SNS injected beam, which will be a 1 GeV 60 Hz H^b eam with a maximum average beam current of 2 mA (or 32 mA over a beam pulse). The tested foils included commercial carbon foils (made by Arizona Carbon Foil Co.), LANL carbon foils (by the mCADAD method), and diamond films prepared from a silicon wafer with a diamond film coating (made by Goodfellow Corp.). Foils were either single-layered or double-layered and were either with or without carbon fiber supports. The results showed that the diamond film had the longest lifetime. The relationship between the foil lifetime and the expected maximum temperature on the foil is also presented in the paper, using the 200 μg/cm² thick Arizona carbon foils, which are supported by 5 μm diameter carbon wires