Extended-MHD dynamics of a Wide Pedestal Quiescent-H mode DIII-D plasma

Abstract We present nonlinear simulations of a Wide Pedestal QH (WPQH)-mode DIII-D plasma with the NIMROD code. We use a full extended-MHD model that retains shear Alfvén and magnetoacoustic waves and includes two-fluid, ion gyroviscosity, cross heat flux, electron inertia, and ion multispecies collisional effects. The steady-state transport calculations use novel-to-MHD local relaxation sources. First, we perform a nonlinear simulation without the fluctuation-induced transport to understand the role of our local relaxation sources. In these simulations, the sources constrain the profiles in the outboard midplane and they remain close to the experimental fits. Second, a nonlinear simulation including the fluctuation-induced transport is carried out. The n ≠ 0 modes flatten the pedestal gradient profiles, however they approximately remain within the experimental error bars. The global dynamics are mediated by both low-n and intermediate-n mode numbers. The local dynamics, though, are much more complicated. The largest-amplitude mode numbers depend on both the MHD-field examined and the spatial location. At the pedestal top, the modes rotate in the E x B/electron diamagnetic drift direction, whereas at both the pedestal bottom and scrape-off layer, the modes rotate in the ion diamagnetic drift direction. The simulation qualitatively agrees with electron cyclotron emission imaging and beam emission spectroscopy measurements. Examination of the convective cross phase indicates that, in WPQH-mode plasmas, energy and particle transport can be mediated by non-ideal, extended-MHD intermediate-n modes, highlighting the critical role of extended-MHD dynamics in pedestal transport.