WALL CONDITIONING EXPERIMENTS ON TFTR USING IMPURITY PELLET INJECTION

This work describes experiments intended to optimize the limiter condi tioning for TFTR supershots. It is shown that deposition of thin layer s of lithium on the limiters by impurity pellet injection changes the plasma-wall interaction and improves supershot performance. Series of up to ten Ohmic plasmas each with two lithium pellets were useful in p re-conditioning the limiter. Generally, plasma performance increased w ith the amount of lithium deposited up to the maximal amount which cou ld be deposited. Experiments were performed with different materials b eing deposited (carbon, boron and lithium) and with different methods of deposition.