HELIUM RETENTION PROPERTIES OF PLASMA-FACING MATERIALS

In a fusion reactor, the continuous removal of helium from the core pl asma is needed in order to sustain the ignition condition. For this pu rpose, it has been proposed to place helium selective pumping metals, which can trap more helium than hydrogen, in the vicinity of the diver tor. In this study, the helium and hydrogen trapping properties of nic kel, tungsten, molybdenum. SS 304 and Inconel 625 were examined. Namel y, the dependencies of irradiation temperature on the amount of trappe d helium and hydrogen were obtained by thermal desorption spectroscopy (TDS), after helium or hydrogen plasma irradiation. In those metals, nickel showed the most suitable selective pumping capability. Nickel h ad the helium selective pumping property above 100 degrees C. The maxi mum amount of trapped helium was (2-3) x 10(16) He/cm(2) at an irradia tion temperature of 200 degrees C and 600 degrees C. The optimum tempe rature becomes about 600 degrees C when nickel is used for a selective pumping material.