CONFINEMENT AND FUELING STUDIES DURING ADDITIONAL HEATING PHASE IN THE JFT-2M TOKAMAK

Increments of peripheral hydrogen/deuterium neutral gas pressures during the additional heating phase (neutral beam and RF heatings) have been observed in a D//2 gas-puff fueled JFT-2M tokamak with H//2-absorbed graphite limiters/divertor plates. In the beam heating phase, a large increment of P//H//2 raises the plasma density 2 times or more without the degrading energy confinement time. The D//2 gas-puff valve is closed in this phase. This improvement is interpreted as being due to 'wall fueling', i. e. , fueling by desorbed hydrogen from the graphite wall by energetic particles. The first observation of the H-mode in the INTOR-type stubby open divertor with a short divertor channel (1-8 cm) at the high density regime (4 minus 7 multiplied by 10**1**3 cm** minus **5) enhanced by the wall fueling is presented. The improved energy confinement time is comparable to or higher than that of ohmically heated discharges.