Time Evolution of the H-mode Pedestal Characteristics in Type I ELM Discharges on DIII-D

The time evolution of H-mode pedestal profiles leading up to a Type I edge localized mode (ELM) is studied in low ELM frequency discharges with electron cyclotron or neutral beam heating. A continuous increase of the pedestal pressure gradient, $\nabla p^{PED}$, and/or the edge transport barrier, ETB, width was observed in all cases. Simulations and Li-beam measurements indicated a continuous increase in pedestal current, resulting in conditions consistent with destabilization of a peeling-ballooning mode. $P^{PED}$ evolution was dominated by changes in the $n_e$ profile while $T_e$ stopped evolving after about 25\% of the inter-ELM period, near the time of onset of density fluctuations observed by BES. However the $T_e^{PED}$ and $\nabla T_e$ varied with heating power. $P^{PED}$ in higher $I_p$ discharges grew mainly through $\nabla p$ increases. In this case $\nabla p$ was below the KBM limit predicted by the EPED model early in the inter-ELM period, although all cases were near the EPED predictions at the ELM. The evolution of $n_e$ and $T_e$ in higher $I_p$ cases was consistent with the paleo-classical model predictions.