ANALYSIS OF TDEV GUARD LIMITERS BY SURFACE SPECTROSCOPIES

In this study we have analysed coupons cut from one of the internal co mponents of the TdeV tokamak, the stainless-steel side sheeting of a g uard limiter, which was removed when the tokamak was modified at the e nd of 1988. Depth profiles of the accumulated layer of contaminants ha ve been compiled by a variety of surface analytical techniques, includ ing Auger electron spectroscopy, elastic recoil detection and scanning electron microscopy. Melting, arcing, bubbles and large exfoliated la yers of coating are observed on the surface of the guard limiter. The damage becomes less severe with increasing distance from the plasma an d disappears near the wall. The deposits consist of a mixture of carbo n, 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-st eel foils that form a frame around the guard limiter, whereas the Inco nel bars were relatively untouched. The metal concentration is a maxim um 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 la yer consists mainly of 'amorphous' carbon.