Effect of heavy ion pre-irradiation on blistering and deuterium retention in tungsten exposed to high-fluence deuterium plasma

Surface blistering and deuterium (D) retention of heavy ion pre-irradiated (1 dpa) tungsten (W) exposed to low-energy (40 eV) and high-flux (1-2 × 1022 D/m2s) D plasma has been investigated with low fluence of 0.1 × 1027 D/m2 and a high fluence of 2.2 × 1027 D/m2. Surface morphology observations show that a large number of blisters are formed on the undamaged W after low-fluence exposure while the area density of the blister will have significantly increased and blister bursting will be triggered in the case of high-fluence exposure. In contrast, the heavy ion pre-irradiation noticeably reduces the area density of blisters for both low- and high-fluence exposures. The thermal desorption spectroscopy (TDS) shows that the total D retention in the pre-damaged W is greater than that of the undamaged sample, and this trend is more significant with increasing fluence/duration of D plasma exposure. The results of positron annihilation Doppler broadening spectrometry (PA-DBS) and TDS indicate that a large number of vacancy-type defects, especially those with a higher trapping energy of D, are induced by the heavy ion pre-irradiation. The increasing defects/D-trap sites may result in two outcomes, the D concentration will disperse at each blister nucleation site and D inward diffusion is enhanced and, therefore, lead to the mitigation of D-induced blistering and increase the D retention. In addition, combined with the enhanced D inward diffusion caused by increasing exposure duration, the D retention is therefore much higher in the pre-damaged W in the case of high-fluence exposure.