Wall pumping and saturation in divertor tokamaks

Asakura, Nobuyuki

Particle control of the main plasma density and exhaust of impurities ions have been demonstrated using the divertor pumping under saturated divertor condition. In JT-60U, ELMy H-mode operation was recently extended to 30s (with NB heating of 8-14 MW). Total number of injected particles reached (1-4)x1023 to maintain high densities. During the long pulse ELMy H-mode of JT-60U, gas puff rate was decreased from 15 to 3Pam3/s, while pumping rate was relatively constant of ~10 Pam3/s. Thus, the divertor plate was mostly saturated. It was found that 40-50% of the injected D was retained, which are comparable to Tore-Supra long pulse and JET high density ELMy H-mode pulse. Particle balance for long pulse and/or high density plasmas are discussed. Carbon flux generated by the chemical process was increased due to increase in the target temperature. Carbon generation and carbon ion emission were gradually increased in the outer leg of the divertor and the X-point. Shielding effect of the divertor was sustained and increment of the radiation power fraction was small in 30s.