H-mode operation is the choice for next step tokamak devices based either on conventional or advanced tokamak physics. This choice, however, comes at a significant cost for both the conventional and advanced tokamaks because of the effects of edge localized modes (ELMs). ELMs can produce significant erosion in the divertor and can affect the beta limit and reduced core transport regions needed for advanced tokamak operation. Experimental results from DIII-D over the past four years have

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... ated a new operating regime, the quiescent H-mode regime, which solves these problems. QH-mode plasmas have now been run for over 4!s (>30 energy confinement times). Utilizing the steady-state nature of the QH-mode edge allows us to obtain unprecedented spatial resolution of the edge ion profiles and the edge radial electric field E r by slowly sweeping the edge plasma past the viewpoints of the charge exchange spectroscopy system. We have investigated the effects of direct edge ion orbit loss on the creation and sustainment of the QH-mode. Direct loss of ions injected into the velocity-space loss cone at the plasma edge is not necessary for creation or sustainment of the QH-mode. The direct ion orbit loss has little effect on the edge E r well. The E r at the bottom of the well in these cases is about -100!kV/m compared to -20 to -30!kV/m in standard H-mode. The well is about 1!cm wide, which is close to the diameter of the deuteron gyro-orbit. We also have investigated the effect of changing edge triangularity by changing the plasma shape from upwardly biased single null to magnetically balanced double null. We have now achieved QH-mode in these double-null plasmas. The increased triangularity allows us to increase pedestal density in QH-mode plasmas by a factor of about 2.5 and overall pedestal pressure by a factor of two. Pedestal beta and " * values matching the values desired for ITER have been achieved. In these higher density plasmas, the E r well is significantly shallower and broader.