Measurement of continuous degradation of a stripper foil during ths operation with 300 kW beam power in the 3-GeV RCS of J-PARC

In the 3-GeV rapid cycling synchrotron of Japan Proton Accelerator Research Complex, we have clearly measured a continuous degradation of a stripper foil during more than 6 months operation with a beam power of 300 kW. A hybrid-type boron doped carbon stripper foil of 200 μg/cm2 was used for 181 MeV H− stripping injection. In order to know an absolute change of the foil thickness as well as information on the pinhole formation, we precisely measured an absolute change of the partially-stripped H0 and the un-stripped H− waste beams. Two absolutely independent monitor systems were used and the results were found to be very consistent with each other. The foil thickness at the injected beam spot was measured to be gradually thickening and it was more than 10 % thicker at the end compared to the initial thickness, where the measurement accuracy was obtained to be better than 2 %. The missing un-stripped H− were also measured to be gradually increasing due to foil deformation and curling but there was however no clear indication of foil thinning or pinhole formation.