Showing papers by "Tatsuo Sugie published in 1990"

Observation of the limiter H mode in the JT-60 tokamak with lower-hybrid current drive

Abstract: The {ital H} mode was achieved in limiter discharges of a tokamak with lower-hybrid current drive for the first time. Simultaneous application of rf powers at two different frequencies such as 1.74 and 2.23 GHz or 1.74 and 2.0 GHz appeared to be effective in the attainment of the {ital H} mode. The threshold lower-hybrid power was as low as Ohmic-heating power with hydrogen plasmas. A nearly steady-state edge-localized-mode-free {ital H} mode with a duration up to 3.3 sec was established without significant impurity accumulation.

Measurements of neutral beam stopping for hydrogen and helium in the JT-60 plasma

Abstract: Shine-through for hydrogen and helium beams in a plasma was measured. Shine-through for an atomic hydrogen beam with f1:f2:f3=7%:32%:61% (where f1, f2 and f3 represent fractions of the full, half and third energy, respectively) and a full energy of 140 keV, was smaller than the value predicted by usual cross-sections without inclusion of excitation processes at an electron density (ne) above 3*1013 cm-3. A fractional beam stopping increment ( delta ), which was defined by delta =( sigma s- sigma s(0)) sigma s(0) (here sigma s was an experimental stopping cross-section and sigma s(0) was the cross-section without including multistep processes via excited states), was about 0.2 at ne=(3.1-5.0)*1013 cm-3 and Zeff=1.6-2.5. The value of delta was consistent with the calculation by Janev et al. (1989, Nucl. Fusion 29, 2125). For a 160-190 keV helium beam, the enhancement of the stopping cross-section was not observed, as expected.

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

Abstract: Helium ash exhaust characteristics have been studied in the JT-60 lower divertor with ohmic heating (OH) and neutral beam heating (NBH) of PNB ≦ 18 MW and Ip = 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.