Confinement and fueling studies during additional heating phase in the JFT-2M tokamak

Regime of improved confinement in neutral-beam–heated limiter discharges of a tokamak

“…This is different in the phase with additional heating. 6 The density dependence of the L-mode incremental confinement time obtained here contradicts the claim of Ref. 15 where no dependence on the density is reported.…”

“…2 Secondly, the control of the pressure of neutral particles and of the particle recycling at the plasma edge yields the transition from L mode to H mode or vice versa in the following experiments: Doublet-Ill LR (low recycling) divertor experiment, 3 poloidal divertor open/ closed-divertor experiment, 5 Doublet-Ill P-mode/Hmode experiment, 10 and JFT-2M non-neutral-buildup divertor experiment. 6 These experiments imply that the plasma-edge cooling by impurities or by neutral particles prevents the development of the H mode in limiter discharges.…”

“…6 For a discharge with an international-tokamak-reactor-type stubby open divertor, x l the H mode is observed first for relatively low beam power (about 0.2 MW of the minimum threshold power). 6 With use of a similar fueling situation the //-mode-type discharge is observed now even in limiter discharges.…”

“…3(a) and 3(b). In the OH phase, T£ ,am increases in proportion to n e up to a critical density (Fie = 2.0x 10 13 cm -3 ; above this limit the peripheral neutral pressure builds up 6 ) and saturates at around 40 ms. This degradation of rjf lam , or Ohmic stored energy Won, is always accompanied with the enhancement of radiative cooling as shown in Fig.…”

“…The discharges with enhanced energyconfinement time (first discovered in the Asymmetric Divertor Experiment tokamak as the H mode 2 and then in other medium-size tokamaks [3][4][5][6] ) provide the possibility of overcoming this problem. Since the energyconfinement times of Ohmic, H-and L-mode discharges are comparable at low density, an //-mode discharge is defined here as a discharge with sudden transitions.…”