H-MODE PEDESTAL CHARACTERISTICS, ELMS, AND ENERGY CONFINEMENT IN ITERSHAPE DISCHARGES ON DIII-D

The H-mode confinement enhancement factor, H, is found to be strongly correlated with the height of the edge pressure pedestal in ITER shape discharges. In discharges with type I edge-localized modes (ELMs) the pedestal pressure is set by the maximum pressure gradient before the ELM and the width of the H-mode transport barrier. The pressure gradie nt before type I ELMs is found to scale as would be expected fora stab ility limit set by ideal ballooning modes, but with values significant ly in excess of that predicted by stability code calculations. The wid th of the H-mode transport barrier is found to scale equally well with pedestal rho POL2/3 or beta(POL)(1/2) The improved H value in high-be ta(POL) discharges may be due to a larger edge pressure gradient and w ider H-mode transport barrier consistent with their higher edge balloo ning mode limit. Deuterium puffing is found to reduce H, which is cons istent with the smaller pedestal pressure which results from the reduc ed barrier width and critical pressure gradient. Type I ELM energy los s is found to be proportional to the change in the pedestal energy.