Experiments on TFTR supershot plasmas

Improvements to the TFTR limiter have extended the threshold for carbon blooms (an uncontrolled massive influx of carbon) to greater than 32 MW for 1 s so that blooms seldom occur in present TFTR supershot experiments. As a result of the progression from strong blooms to modest blooms to no blooms, improvements in confinement could be correlated with the occurrence of a carbon bloom in the plasma which immediately preceded the supershot. It is speculated that the carbon influx during a carbon bloom results in a limiter surface which has a slightly reduced self-sputtering yield for the subsequent discharge. The influence on the supershot plasma seems similar to phenomena obtained by conditioning with lithium pellets.