Development of vacuum transfer techniques for tokamak in-situ surface analysis

Plasma-wall interactions in tokamaks can in general be divided into atomic scale and grain size effects. The former class of effects include desorption, sputtering, recoil doping, and other related subjects, while the latter includes larger scale phenomena such as blistering, flaking, cracking and evaporation. These latter effects can be analysed using conventional metallurgical techniques. However, atomic scale processes require that the samples be maintained and analysed in a vacuum environment since monolayer changes can occur in minutes at 10-6 Pa (approximately=10-8 Torr). For this reason it is essential that surface analysis either be done in the tokamak during or briefly after a discharge or the surface of interest should be quickly transferred under vacuum to an ultra high vacuum (UHV) instrument for immediate analysis. However, under certain conditions it is desirable to transfer exposed samples or specially prepared substrates under vacuum for analysis in other UHV instruments not on-line. This requires the use of an ultra high vacuum transfer device (VTD). (Auth.)