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

## TL;DR

This study uses nonlinear MHD simulations to model DIII-D QH-mode discharges, revealing turbulent states and transport behaviors consistent with experiments, but highlighting the need for more advanced modeling to match observed rotation frequencies.

## Contribution

It demonstrates the importance of flow in MHD modeling of QH-mode and compares simulation results with experimental observations, emphasizing the need for improved modeling of plasma rotation.

## Key findings

- Simulations saturate into turbulence without flow, matching experimental quiescent behavior.
- Turbulent modes evolve through inverse cascade, with dominant modes changing over time.
- Particle transport is significantly larger than thermal transport, consistent with experiments.

## Abstract

Extended-MHD modeling of DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] quiescent H-mode (QH-mode) discharges with nonlinear NIMROD [C. R. Sovinec et al., J. Comput. Phys. 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=1 and 2 toroidal modes become dominant through an inverse cascade. Each mode in the range of n=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 that rotation frequencies differ between the simulation and experiment, which indicates that more sophisticated extended-MHD two-fluid modeling is required.