Influence of neon seeding on the deuterium retention and surface modification of ITER-like forged tungsten

Abstract

In order to investigate the effect of neon seeding on deuterium retention and surface modification of ITER-like forged tungsten with grains elongated perpendicular to the surface, pure and neon-seeded deuterium plasma exposures were performed in the linear plasma device PSI-2. The ion percentage of neon in the mixed plasma was around 10%. The sample temperature and deuterium ion fluence were kept at 450 K and 1 × 1026 m−2, respectively. The incident ion energy was 40 eV, just reaching the tungsten sputtering threshold for neon. Surface observations show that neon seeding leads to pronounced cracking and erosion of blister caps and a significant reduction of small blisters (<0.8 μm). This is possibly attributed to surface sputtering and the inhibitory effect of neon-induced defects on blister nucleation by hindering dislocation movements. On the other hand, neon seeding increases the total deuterium retention by ∼70% according to the thermal desorption spectroscopy (TDS) measurements. A low-temperature desorption peak (∼660 K) which should be mainly ascribed to deuterium de-trapping from dislocations is observed to be broadened and shifts towards higher temperature in the case of neon seeding, suggesting enhanced inward diffusion and trapping of deuterium. An additional deuterium release peak appears at a higher temperature (∼803 K), indicating the creation of new deuterium-traps induced by neon. A comparison of the results of nuclear reaction analysis and TDS reveals that neon seeding not only increases deuterium retention in the surface region (<7.2 μm) but also in the bulk (>7.2 μm). We ascribe the enhanced deuterium retention to the increased deuterium-traps in the top-surface induced by Ne irradiation and the vertical grain boundary configuration of the forged W promoting the inward diffusion of deuterium.