Deuterium release and microstructure of tantalum-tungsten twin limiter exposed in TEXTOR-94

Ta-W twin limiter experiments had been carried out in TEXTOR-94. D(beta) and D(gamma) intensities were observed during discharges. As a result, the intensities from the Ta surface were less than those from the W surface. This is attributed to the release ratio of molecules and atoms from the surface, i.e. less atomic release and more molecular release from Ta. Concerning long term D retention in Ta, D distributed uniformly over the limiter and the content was about 4 x 10(-5) D per Ta atom. The total amount in the Ta limiter was estimated 3 x 10(20) D in the half limiter. After exposure, the Ta bulk showed a significantly modified surface: grain growth, wrinkle like deformations and local recrystallization. However, open cracks were not observed in Ta exposed in the same condition in which W created big open crack. (C) 2002 Elsevier Science B.V. All rights reserved.