Helium retention of nickel

Abstract In a fusion reactor, in order to enhance the pumping efficiency for helium ash, the use of a metal such as nickel has been conceived because of its capability to selectively retain helium. In the present study, the nickel was irradiated by He plasma, H 2 plasma or both by H 2 and He plasma, in the ECR plasma irradiation apparatus. The range of the helium fluence and irradiation temperature were about 4 ∼ 5 × 10 18 He/cm 2 and from RT to 700°C, respectively. The amount of trapped helium was examined by the thermal desorption spectroscopy (TDS) technique. The retained hydrogen rapidly decreased with the irradiation temperature, and no retention was observed for temperatures higher than 100°C. In the TDS spectrum, several helium desorption peaks appeared in the low temperature region (200 ∼ 700°C), and the dominant peak at high temperature was about 800°C. The total amount of helium retained as a function of irradiation temperature, had two peaks at 100 ∼ 200 and 500 ∼ 600°C. It is suggested that the optimum temperature for the selective pumping of helium thus becomes 500 ∼ 600°C, since the nickel may be used on the vacuum chamber where the temperature is higher than about 300°C.