TFTR confinement results

The characteristics of plasma operation on the axisymmetric inner toroidal limiter in TFTR are described. After a conditioning procedure, plasmas with low metal content and low zsub(eff) have been obtained with this limiter. There is no substantial increase in Zsub(eff) with total input power during neutral beam injection. Compared to operation on the outer blade limiter, additional gas is required to fuel plasmas on the inner limiter, but not by a large factor. Injection of deuterium pellets has increased the plasma density substantially and produced energy confinement times up to 0.5s in ohmically heated plasmas. The four neutral beam lines have injected up to 13.5MW total power into the plasma for 0.5s with up to 90kV accelerating voltage. The scaling of the plasma stored energy has been studied as a function of the input power, plasma current and plasma density. In the range 1.4 to 2.2 MA, the overall and incremental confinement times for both the total and thermal stored energies increase with plasma current at fixed density. There appears to be a weak negative scaling of the total stored energy, determined magnetically, with density at high injection power. (author)