Temperature impact on W surface exposed to He plasma in LHD and its consequences for the material properties

A new temperature controlled material probe was designed for the exposure of W samples to He plasma in the LHD (Large Helical Device). TEM (Transmission Electron Microscopy) analysis allowed the study of the impact of He irradiation under high temperatures (up to 600 °C) on W microstructure: bubbles and dislocation loops are formed at the surface. A heavily damaged layer rich in both damages is formed at the very surface layer whose thickness increases with the incident fluence; beyond this layer, bubbles are observed much deeper than expected, rising concerns about the consequences for the material properties conservation. Nano-indentation measurements showed that the hardness of exposed tungsten indeed increases as the dislocation loops are formed and large bubbles appear in the material.