REFLECTION, REEMISSION AND PERMEATION OF DEUTERIUM IMPLANTED IN TI-6AL-4V ALLOY

A Ti-6Al-4V alloy has been selected as the vacuum vessel structural ma terial in the tokamak physics experiment (TPX) [1] and in the steady s tate tokamak JT-60 Super Upgrade (JT-60 SU) [2]. To determine the amou nt of hydrogen retained in titanium alloy during glow discharge cleani ng and plasma operation the knowledge of the parameters such as a reco mbination coefficient K and a particles reflection coefficient R-N is necessary. Presence of the non-metallic impurities on the surface stro ngly affects both the above mentioned parameters. In the present work, the permeation behavior of deuterium has been investigated for deuter ium implanted into Ti-6Al-4V membrane with an incident ion energy 150- 1500 eV/D. R-N has been determined by means of the thermal desorption technique. The surface chemical composition was controlled in-situ by means of AES and SIMS analyses. Experimentally obtained values of R-N are larger than computer simulation results for both the clean Ti-6Al- 4V surface and the surface layer with the concentration of the chemica l elements same as that experimentally observed. The calculated values of R-N are not significantly different from one another, The amount o f retained hydrogen was estimated for TPX condition taking into accoun t the contribution of the reflected particles to the flux balance.