Deuterium retention in recrystallized tungsten exposed to high-flux plasma with fluences up to 1×1029 m-2

Plasma fluence at the divertor of a future magnetic confinement fusion device can accumulate up to ~1028-1029 m-2 per year. Yet hydrogen isotope retention under such high-fluence plasma exposure has been rarely reported. To investigate deuterium (D) retention in tungsten (W) exposed to such high-fluence plasma, a series of high-flux D plasma exposures were preformed using recrystallized W samples at ~500 K in Magnum-PSI. The highest fluence achieved was ~1×1029 m-2. Surface morphology observations indicate an initial increase in the number of blisters at the sample surface with increasing fluence, followed by saturation at ~1×1029 m-2. Multiple bursts of blisters with open cracks or edges were observed under the two highest fluences of ~1×1028 m-2 and ~1×1029 m-2. 3He nuclear reaction analysis (NRA) shows a maximum D concentration up to 0.012 at.fr., distributed within the first 4 μm from the sample surface under the highest fluence. D retention, as measured by NRA and thermal desorption spectroscopy, tends to saturate with increasing fluence. Simulations of D2 thermal desorption, performed using the TMAP rate equation code, show a maximum D trapping depth of ~10 µm, consistent with the defect depth profile revealed by transmission electron microscopy. D retention saturation observed in this work is attributed to the sample surface morphology modifications and the saturation of plasma-induced defects. This investigation provides a valuable reference for understanding the evolution of total hydrogen isotope retention in W under high-fluence plasma exposure in future fusion devices.