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

Abstract

Extended-MHD modeling of DIII-D tokamak quiescent H-mode (QH-mode) discharges with nonlinear NIMROD 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. As a result, 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.

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2];  [2];  [2];  [2];  [3];  [4];  [2]
  1. Tech-X Corp., Boulder, CO (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Oak Ridge Associated Universities (ORAU), Oak Ridge, TN (United States)
  4. Tech-X Corp., Boulder, CO (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Tech-X Corp., Boulder, CO (United States); General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1347994
Alternate Identifier(s):
OSTI ID: 1348026; OSTI ID: 1406354
Grant/Contract Number:
FC02-06ER54875; AC02-05CH11231; AC02-06CH11357; FC02-04ER54698; FC02-08ER54972
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 5; Conference: manuscript associated with invited talk at APS-DPP Annual Meeting, 2016, in San Jose; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; extended-MHD modeling; quiescent H-mode; peeling-ballooning modes; nonlinear simulation; tokamak pedestal

Citation Formats

King, Jacob R., Kruger, S. E., Burrell, K. H., Chen, X., Garofalo, A. M., Groebner, R. J., Olofsson, K. E. J., Pankin, A. Y., and Snyder, P. B.. MHD modeling of a DIII-D low-torque QH-mode discharge and comparison to observations. United States: N. p., 2017. Web. doi:10.1063/1.4977467.
King, Jacob R., Kruger, S. E., Burrell, K. H., Chen, X., Garofalo, A. M., Groebner, R. J., Olofsson, K. E. J., Pankin, A. Y., & Snyder, P. B.. MHD modeling of a DIII-D low-torque QH-mode discharge and comparison to observations. United States. doi:10.1063/1.4977467.
King, Jacob R., Kruger, S. E., Burrell, K. H., Chen, X., Garofalo, A. M., Groebner, R. J., Olofsson, K. E. J., Pankin, A. Y., and Snyder, P. B.. Tue . "MHD modeling of a DIII-D low-torque QH-mode discharge and comparison to observations". United States. doi:10.1063/1.4977467. https://www.osti.gov/servlets/purl/1347994.
@article{osti_1347994,
title = {MHD modeling of a DIII-D low-torque QH-mode discharge and comparison to observations},
author = {King, Jacob R. and Kruger, S. E. and Burrell, K. H. and Chen, X. and Garofalo, A. M. and Groebner, R. J. and Olofsson, K. E. J. and Pankin, A. Y. and Snyder, P. B.},
abstractNote = {Extended-MHD modeling of DIII-D tokamak quiescent H-mode (QH-mode) discharges with nonlinear NIMROD 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 nΦ = 1 and 2 toroidal modes become dominant through an inverse cascade. Each mode in the range of nΦ = 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. As a result, 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.},
doi = {10.1063/1.4977467},
journal = {Physics of Plasmas},
number = 5,
volume = 24,
place = {United States},
year = {Tue Mar 07 00:00:00 EST 2017},
month = {Tue Mar 07 00:00:00 EST 2017}
}

Journal Article:
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  • Extended-MHD modeling of DIII-D tokamak quiescent H-mode (QH-mode) discharges with nonlinear NIMROD 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 particlemore » 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. As a result, 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.« less
  • Experiments conducted at DIII-D investigate the role of drift kinetic damping and fast neutral beam injection (NBI)-ions in the approach to the no-wall β N limit. Modelling results show that the drift kinetic effects are significant and necessary to reproduce the measured plasma response at the ideal no-wall limit. Fast neutral-beam ions and rotation play important roles and are crucial to quantitatively match the experiment. In this paper, we report on the model validation of a series of plasmas with increasing β N, where the plasma stability is probed by active magnetohydrodynamic (MHD) spectroscopy. The response of the plasma tomore » an externally applied field is used to probe the stable side of the resistive wall mode and obtain an indication of the proximity of the equilibrium to an instability limit. We describe the comparison between the measured plasma response and that calculated by means of the drift kinetic MARS-K code, which includes the toroidal rotation, the electron and ion drift-kinetic resonances, and the presence of fast particles for the modelled plasmas. The inclusion of kinetic effects allows the code to reproduce the experimental results within ~13% for both the amplitude and phase of the plasma response, which is a significant improvement with respect to the undamped MHD-only model. The presence of fast NBI-generated ions is necessary to obtain the low response at the highest β N levels (~90% of the ideal no-wall limit). Finally, the toroidal rotation has an impact on the results, and a sensitivity study shows that a large variation in the predicted response is caused by the details of the rotation profiles at high β N.« less
  • A stationary, quiescent H-mode (QH-mode) regime with a wide pedestal and improved confinement at low rotation has been discovered on DIII-D with reactor relevant edge parameters and no ELMs. As the injected neutral beam torque is ramped down and the edge ExB rotation shear reduces, the transition from standard QH to the wide pedestal QH-mode occurs. And at the transition, the coherent edge harmonic oscillations (EHO) that usually regulate the standard QH edge cease and broadband edge MHD modes appear along with a rapid increase in the pedestal pressure height (by ≤60%) and width (by ≤50%). We posit that themore » enhanced edge turbulence-driven transport, enabled by the lower edge ExB flow shear due to lower torque reduces the pedestal gradient and, combined with the high edge instability limit provided by the balanced double-null plasma shape, permits the development of a broader and thus higher pedestal that is turbulence-transport-limited. Even with the significantly enhanced pedestal pressure, the edge operating point is below the peeling ballooning mode stability boundary and thus without ELMs. Improved transport in the outer core region (0.8≤ρ≤0.9) owing to increased ExB flow shear in that region and the enhanced pedestal boost the overall confinement by up to 45%. Our findings advance the physics basis for developing stationary ELM-free high-confinement operation at low rotation for future burning plasma where similar collisionality and rotation levels are expected.« less