Characteristics of carbon sheet pump in application experiments to a high-temperature plasma device

Abstract

Carbon sheet pump (CSP), which has been developed for reduction of hydrogen recycling in the large helical device (LHD) of National Institute for Fusion Science, is applied to an actual plasma device for the first time to evaluate the pumping characteristics. A small scale of pump module is manufactured and installed in the GAMMA-10 tandem mirror device and the module is exposed to charge-exchange neutrals emitted from ICRF-heated hot-ion plasmas. Temporal evolution of the pressure is measured with a fast ionization gauge installed in the test chamber during the plasma discharge and a significant difference between CSP-on and CSP-off is observed under good reproducibility. The dependence on the ICRF power is investigated and the pressure difference between on and off is found to increase with the ICRF power. These phenomena indicating the pumping ability of CSP are observed to continue during more than 300 plasma shots, which shows the effectiveness of CSP in controlling hydrogen recycling. The result of thermal desorption experiments of CSP after being exposed to charge-exchange neutrals is also described.