Deuterium retention, blistering and local melting at tungsten exposed to high-fluence deuterium plasma

Blistering, deuterium retention and local melting at tungsten exposed to high-fluence (up to 1027 D/m2) of high-flux (1022 D+/m2/s) and low-energy (38 eV) deuterium plasma at varying temperature were examined with scanning electron microscopy (SEM), focused ion beam (FIB), thermal desorption spectroscopy (TDS) and electron probe microanalysis (EPMA). Blisters with various shapes were observed after the plasma exposure, and both deuterium retention and blistering showed a significant dependence upon the exposure temperature and fluence. Local melting and flakes on some grains were observed even if the heat flux is less than 0.1 MW/m2, suggesting that the local melting is caused by flakes due to the loss of heat conduction between the flakes and the bulk during the plasma exposure.