HYDROGEN-DEUTERIUM RECYCLING AND INITIAL RESULTS OF HELIUM ASH STUDY IN JT-60U

Reduction of particle recycling is an important technique in present plasma devices to improve energy confinement characteristics. Besides obtaining long pulse DT burning plasmas, controlled fuelling of the plasma with the primary species and removal of the helium ash are important issues. In the JT-60U tokamak, about 90% of the inner surface is covered with graphite tiles. Because recycling becomes more important with graphite surfaces, recycling characteristics of an all graphite first wall is important. In this paper, experimental results of JT-60U on recycling and helium ash removal are presented. The effect of wall temperature on recycling was observed. Significant hydrogen dilution was observed during deuterium discharges. Recycling characteristics in the ELMy H-mode discharges are also described where the neutral pressure increases with the electron density similar to L-mode discharges. In high betarho/hot ion discharges, a highest neutron production rate of 1.3 X 10(16) s-1 was obtained with the lowest recycling. Initial results of helium ash experiment with strong He gas puffings in ohmically and neutral beam heated discharges are reported.