The dependence on ion energy and temperature of helium trapping in nickel

The reduction of helium concentration in the core of the plasma is a major issue to control the fusion reaction. Nickel has been proposed to be used i n the vicinity of the divertor as a helium selective pumping material. In t his study, the amount of trapped helium in nickel after helium plasma irrad iation was measured by thermal desorption spectroscopy (TDS). The incident energy of helium ion was adjusted by the negative bias voltage. The depende nce of the trapped amount of helium on the helium incident energies was stu died using different irradiation temperature. Besides a peak at low tempera ture, desorption peaks of helium appeared in the high temperature region wh en the energy of the helium ion is relatively high. For irradiation tempera tures below 400 degrees C, the amount of trapped helium increased linearly with the energy of the helium ion. For irradiation temperatures higher than 500 degrees C, the trapping of helium needed of relatively high incident i on energies. The dependence of the amount of trapped helium on the irradiat ion fluence was also investigated. (C) 1998 Elsevier Science B.V. All right s reserved.