Helium pumping properties of nickel and tungsten

Abstract In order to reduce helium ash concentration in a core plasma of fusion reactor, it has been proposed to place the helium selective pumping metals in the vicinity of the divertor. It is known that metals such as nickel and tungsten may trap helium particles selectively, compared with the fuel hydrogens. In this study, the helium trapping properties of those metals, namely, the dependences of irradiation temperature, helium fluence and helium energy, were examined by a technique of thermal desorption spectroscopy, after the helium and the hydrogen plasma irradiations. It was observed that nickel selectively pumped the heliums but the helium pumping amount of tungsten was comparable with that of the hydrogens. For the case of nickel, a suitable temperature to selectively pump the helium was about 600 °C and the saturation level (2–;3) × 10 16 He cm −2 when the helium acceleration voltage was −1 kV. Based on these results for the case of nickel, it may be possible to consider rough design parameters.