Positron annihilation study of tungsten exposed to low-energy deuterium plasma

Hirade, Tetsuya  ; Furuta, Hikaru*; Torikai, Yuji*; Fujimura, Yuki; Michishio, Koji*

Positron annihilation lifetime (PAL) measurements by use of a positron source of Na were performed for polycrystalline ITER-grade tungsten samples exposed to low-energy deuterium plasma. The energy of deuterium plasma was low and then it was expected that it would affect just near-surface region. However, we obtained the longer mean positron annihilation lifetime in the tungsten samples exposed to the low-energy deuterium plasma than the virgin tungsten samples. Moreover, almost same longer values were obtained even on the other (no exposed) side of the samples, although the thickness of the samples were about 2 mm. Although, there has been no report of observation of defect formation by existence of hydrogen or deuterium in tungsten, the results indicated that deuterium existence in tungsten can be one of reasons of defects formation.