MHD modeling of a DIII-D low-torque QH-mode discharge and comparison to observations

Abstract

Extended-MHD modeling of DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 2002] QH-mode discharges with nonlinear NIMROD [C. R. Sovinec et al., JCP 195, 355 2004] simulations saturates into a turbulent state, but does not saturate when the steady-state flow inferred from measurements is not included. This is consistent with the experimental observations of the quiescent regime on DIII-D. The simulation with flow develops into a saturated turbulent state where the n φ =1 and 2 toroidal modes become dominant through an inverse cascade. Each mode in the range of n φ =1-5 is dominant at a different time. Consistent with experimental observations during QH-mode, the simulated state leads to large particle transport relative to the thermal transport. Analysis shows that the amplitude and phase of the density and temperature perturbations differ resulting in greater fluctuation-induced convective particle transport relative to the convective thermal transport. Comparison to magnetic-coil measurements shows rotation frequencies differ between the simulation and experiment which indicates that more sophisticated extended-MHD two-fluid modeling is required.

The JOREK non-linear extended MHD code and applications to large-scale instabilities and their control in magnetically confined fusion plasmas

“…Section 5.7 finally, contains a very brief outlook. For investigations of ELMs and ELM control with other non-linear MHD codes, refer to the review provided in reference [3] and for more recent work to references [181][182][183][184][185][186][187][188][189][190][191] and references therein.…”

Impact of rotation and ion diamagnetic drift on MHD stability at edge pedestal in quiescent H-mode plasmas

“…Nonlinear simulation with the JOREK code solving the reduced MHD model derived from the visco-resistive MHD equations also showed that the kink/peeling mode is the most unstable mode and is saturated non-linearly in QH-mode plasmas [8,9]. Nonlinear simulation using the NIMROD code with a resistive MHD model including an anisotropic stress tensor and anisotropic thermal heat conduction did not identify the branch of MHD mode unstable in a DIII-D QH-mode plasma, but indicated that MHD modes with low toroidal mode numbers are unstable and can be saturated as quasi-turbulent state when taking into account plasma rotation [10], where an MHD mode with low toroidal mode number is usually current-driven one.…”

Excitation Mechanism of Low- n Edge Harmonic Oscillations in Edge Localized Mode-Free, High Performance, Tokamak Plasmas

“…The excitation mechanism of such instabilities is still unclear. Previous theoretical interpretations suggested that short wavelength modes exhibiting infernal features [13][14][15][16], though dominant in the linear phase, were suppressed nonlinearly and superseded by steady low-n modes [17,18] with no significant effects of the parallel flow [17,19]. Recent experimental findings point to the E × B shearing rate as the key ingredient for the development of the characteristics of these oscillations [19].…”