Initial Results of Helium Ash Experiment in the JT-60 Lower Divertor

Helium ash exhaust characteristics have been studied in the JT-60 lower divertor with ohmic heating (OH) and neutral beam heating (NBH) of P_NB ≦ 18 MW and I_p = 1 MA. Helium fueling was done by gas puff. The divertor neutral pressures of hydrogen (H₂) and helium were measured by a residual gas mass analyzer. The helium enrichment in the divertor was also measured. In OH discharges with helium gas puff, no buildup of helium neutral pressure was observed and helium was depleted. On the other hand, in NBH discharges with helium gas puff although enrichment of helium is not observed, the neutral pressures of H₂ and helium increase in proportion to . The density dependence of the helium neutral pressures in NBH discharges is promising for efficient helium ash exhaust in fusion reactors.