Thermal desorption characteristics of several charge stripper carbon films for J-PARC RCS

Multi-turn H^- beam injection method is used in the J-PARC 3 GeV synchrotron to match the incident beam and the circulating beam. In this method, two electrons of the H^- beam from the Linac are stripped by passing through the carbon thin film at the beam injection point. The remaining protons are made to go around and combined with the next injection beam bunch to increase the beam intensity. During the beam injection, the charge stripping thin film is heated due to the beam energy deposition in the film and the outgassing is released. Therefore, investigating of the outgassing characteristics of the charge stripping thin films is essential for maintaining the beam line at ultra-high vacuum. Released outgassing from heated thin films was measured by thermal desorption spectroscopy. Several types of thin films, which are used or candidate for the injection beam charge stripping films, were prepared as samples. Each type of film showed different outgassing characteristics during the heating. It was found that the heat treatment at high temperature effectively reduced the outgassing even after the films were taken out to the atmosphere. For the thin film formed by the vacuum evaporation method, the bake-out at 100°C was effective to reduce the outgassing other than hydrogen. The results of this survey gave the guide to not only the outgassing reduction process but also the improvement of the making process of the thin films. (author)