Quantitative monitoring of the stripper foil degradation in the 3-GeV rapid cycling synchrotron of the Japan proton accelerator research complex

A hybrid-type boron doped carbon stripper foil of 200 μg/cm 2 is used for the present H − injection beam energy of 181 MeV in the 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC). A stripper foil has a certain lifetime and usually lifetime goes shorter for high power operation. Foil degradation such as foil thinning and pinhole formation caused by the radiation might be a signal of the foil breaking. As a result, one can avoid sudden foil breaking by an efficient monitoring of the foil degradation. We have succeeded measuring even a little change of the stripper foil thickness during user operation of the RCS. It is the main motivation of the present study. A single foil was irradiated with a total of 2.7 × 10 21 particles (injected H − itself) during 4 months continuous operation of the RCS but we did not observe any indication of the foil degradation.