Hydrogen concentration of co-deposited carbon film produced in the vicinity of LHD divertor tiles

Abstract In order to investigate the hydrogen retention and desorption behavior in co-deposited carbon film, a unique sample holder was mounted on the plasma-facing wall close to the graphite divertor tiles in the LHD during the 13th experimental campaign. The amount of deposited carbon for the sample with a large visual angle against the divertor tile was much larger than that with a small visual angle. The amount of retained hydrogen increased with the film thickness, but not proportional to the thickness. The carbon films contained boron caused by boronization and the retained hydrogen was trapped mainly by C–H and B–H bonds. Hydrogen concentration for the carbon film with a large visual angle against the graphite tile was much smaller than that with a small visual angle, possibly owing to the difference of the ratio of hydrogen influx to carbon influx.