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Effects of Steady-State Plasma Exposure on Tungsten Surface Cracking due to Elm-Like Pulsed Plasma Bombardment

D. Nishijima, Y. Kikuchi, M. Nakatsuka, M. J. Baldwin, R. P. Doerner, M. Nagata, Y. Ueda

Fusion Science and Technology / Volume 60 / Number 4 / November 2011 / Pages 1447-1450

Interaction with Materials / Proceedings of the Ninth International Conference on Tritium Science and Technology (Part 2) /

Sequential exposures of W surfaces to steady-state and pulsed (~0.5 ms) plasmas have been performed in a linear divertor plasma simulator and a magnetized coaxial plasma gun to investigate effects of D blisters, nano-sized He bubbles, and He-induced W fuzz on surface cracking by pulsed plasma loads. Surface cracks appeared on samples containing D blisters or He bubbles following 10 shots at ~0.5 MJ/m2 per shot, while a mirror-polished sample with no pre-plasma exposure did not exhibit cracks after similar transient exposures. Note that the cracking is limited to the edge region for a sample with D blisters. This means that the energy density threshold for surface cracking is lowered by the existence of D blisters and, especially, He bubbles. On the other hand, it is found that fuzzy surfaces possess a good resistance to surface cracking, although arcing is prone to occur.

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