In situ measurements of low energy D plasma-driven permeation through He pre-damaged W

Experiments concerning the effect of helium (He) plasma exposure on deuterium (D) plasma-driven permeation through tungsten (W) foils in a linear plasma facility have been performed. 0.05 mm thick W foils were exposed to similar to 2 x 10(20) m(-2) s(-1) He plasma with various fluences at 883 K. After He irradiating, D permeation tests were performed for the samples and retention was also measured by high-resolution thermal desorption spectroscopy. It was observed that He pre-irradiation resulted in a significant reduction of D permeation and retention in W. Microstructure observation indicated that the surfaces of the samples after He irradiation turned rough and He nanobubbles were formed near the surface. Defective structures including He nanobubbles likely enhance D reemission and accordingly reduce the permeation and retention in He pre-irradiated W.