Analysis of TdeV guard limiters by surface spectroscopies

In this study we have analysed coupons cut from one of the internal components of the TdeV tokamak, the stainless-steel side sheeting of a guard limiter, which was removed when the tokamak was modified at the end of 1988. Depth profiles of the accumulated layer of contaminants have been compiled by a variety of surface analytical techniques, including Auger electron spectroscopy, elastic recoil detection and scanning electron microscopy. Melting, arcing, bubbles and large exfoliated layers of coating are observed on the surface of the guard limiter. The damage becomes less severe with increasing distance from the plasma and disappears near the wall. The deposits consist of a mixture of carbon, oxygen, stainless steel and Inconel. Most of the deposited impurity is carbon. Of the deposited metal mixture, only about 6% is Inconel, implying that metal impurities originated mainly from the stainless-steel foils that form a frame around the guard limiter, whereas the Inconel bars were relatively untouched. The metal concentration is a maximum at the surface, coinciding with the maximum concentration of oxygen. Metal carbide appears to be formed with the metal deposits near the surface and at the interface with the substrate, whereas the middle layer consists mainly of ''amorphous'' carbon. (Author)