Effect of ECRH on pedestal structure, turbulence and ELM dynamics in DIII-D

Pedestal structure and instabilities, in different operating scenarios, is a key area of tokamak research as pedestal pressure is a factor for core plasma performance. In DIII-D, ECRH is applied (at $\rho =$0.2) in increments in NBI shots to study the effects of $T_{e}$/$T_{i\thinspace }$\textgreater 1 and density pump-out on the pedestal. For NBI, there are rapid ELMS of varied amplitude, while, for ECRH, the ELM frequency is well-defined, lower than in the NBI shots, and each type-I ELM is followed by one or two very small ELMs. Fast-magnetics show a group of modes at 13\textasciitilde 116 kHz consisting of 3 distinct modes in ECRH shots only. Phase-locked analysis shows that 2 modes at 13\textasciitilde 70 kHz do not grow for the first 10 ms of the inter-ELM period ( $\Delta t=$0\textasciitilde 10 ms, w.r.t. the ELM crash) and then grow to saturation for $\Delta t=$10\textasciitilde 25 ms. Note that $\nabla n_{e}$, $\nabla T_{e}$ and $\nabla p_{e}$ saturate after $\Delta t=$10 ms. These results may indicate that, either $\nabla p_{e}$ needs to reach a certain threshold to trigger the growth of these modes and/or the growth of the modes clamps $\nabla p_{e}$. An alternative possibility is that the changes in $\nabla E_{r}$ (and hence \textbf{E}x\textbf{B}) may affect $\nabla p_{e}$ and/or the modes. Note that changes in rotation have been observed at the pedestal for $\Delta t=$0\textasciitilde 25 ms. Analysis of pedestal recovery, transport and stability with ECRH will be reported.