Analyses and the effect of impurities contained in charge stripper foils for the 3-GeV RCS of J-PARC

In J-PARC, the 3 GeV rapid cycling synchrotron (RCS) applied hybrid type thick boron-doped carbon (HBC) foils as charge stripper in the multi-turn injection. Although HBC foils have successfully operated to provide a high-power beam for experimental users since the operation of the accelerator started, the deformation and radio-activation of the foils occurred as serious problems. We investigated the cause of the problems, as result we found that impurities in the foil led to these phenomena. In this report, we describe why impurities were mixed in the foil, and which kinds of impurities were found by various methods of analysis. The effect of impurities is also discussed. (author)