Progress in two-fluid nonlinear MHD NIMROD modeling of edge harmonic oscillations in DIII-D quiescent H-mode*

Recent nonlinear extended-MHD modeling [1] of low-torque quiescent H-modes discharges on DIII-D yield several insights: a state with low-n modes is only achieved in the presence of the flow inferred from experiment and the amplitude and phase of the perturbations lead to strong density transport relative to thermal losses. However, discrepancies with experimental measurements remain. In this work we extend the modeling of edge harmonic oscillations (EHO) with the NIMROD code to well-diagnosed DIII-D discharges. Similar to the previous NIMROD [1] and M3D-C¹ [2] simulations, the new linear NIMROD results confirm that the flows can destabilize the low-n modes. In this work, the linear NIMROD simulations are continued to nonlinear stages that show the formation of saturated EHO states. The simulations are compared to the electron-cyclotron emission (ECE) measurements. Progress to enable two-fluid modeling is discussed along with a comparison of the nonlinear dynamics of this EHO case relative to the previous NIMROD modeling results which produced a weakly turbulent state.

 

[1] J.R. King et al. Phys. of Plasmas 24, 055902 (2017).
[2] Xi Chen et al. Nuclear Fusion 56, 076011 (2016).