Performance of ICRF-heated D-T plasmas fueled by neutral beam injection in TFTR

The first experiments to heat neutral‐beam‐fueled D‐T plasmas with ICRF were conducted during the past year on TFTR. These experiments were performed with full‐bore (R∼2.62 m) plasmas in the low recycling, ‘‘supershot’’ regime with confinement times exceeding two times the empirical L‐mode value. Up to 6 MW of RF were coupled into plasmas fueled by up to 24 MW of D‐T beam injection. Some discharges utilized all T beam fueling to maximize the effect of the second harmonic tritium absorption. Extensive Li‐pellet injection was employed in this regime in an attempt to reduce wall recycling and improve plasma confinement. Although significant second harmonic tritium heating was seen in some plasmas, many discharges were characterized by a degradation in performance and reactivity early in the neutral beam pulse as a result of enhanced recycling of impurities and deuterium from the carbon tile limiter. The proximity of the outboard limiter appears to have exacerbated attempts to limit this enhanced influx.