NIMROD modeling of quiescent H-mode: reconstruction considerations and saturation mechanism

King, Jacob; Burrell, K.H.; Garofalo, A. M.; Groebner, R. J.; Kruger, Scott; Pankin, A.Y.; Snyder, P. B.

doi:10.1088/0029-5515/57/2/022002

Cited by 13 publications

(17 citation statements)

References 34 publications

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“…This result is surprising as the magnetic field is stochastic within the pedestal (see Ref. [16]). With the highly anisotropic thermal conduction as included in the model, one would naively expect that thermal transport should be enhanced relative to the particle transport instead of the reverse.…”

Section: Transport Analysismentioning

confidence: 99%

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

et al. 2017

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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.

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Section: Transport Analysismentioning

confidence: 99%

“…In Ref. [16], initial analysis of nonlinear NIMROD [17] simulations of a QH-mode discharge with broadband activity is presented.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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“…Ref. [5]), as opposed to modeling the symmetric fields with the full extended-MHD equations (e.g. Ref.…”

Section: Introductionmentioning

confidence: 99%

“…One notable case that uses this method is the DIII-D QH-mode modeling in Ref. [5]. The difficulties with the current and flow discontinuities and a desire for more accurate modeling of the QH-mode instabilities motivated the development of our methods that include SOL profile gradients.…”

Section: Introductionmentioning

confidence: 99%

Effect of scrape-off-layer current on reconstructed tokamak equilibrium

et al. 2017

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Methods are described that extend fields from reconstructed equilibria to include scrape-off-layer current through extrapolated parametrized and experimental fits. The extrapolation includes both the effects of the toroidal-field and pressure gradients which produce scrape-off-layer current after recomputation of the Grad-Shafranov solution. To quantify the degree that inclusion of scrapeoff-layer current modifies the equilibrium, the χ-squared goodness-of-fit parameter is calculated for cases with and without scrape-off-layer current. The change in χ-squared is found to be minor when scrape-off-layer current is included however flux surfaces are shifted by up to 3 cm. The impact on edge modes of these scrape-off-layer modifications is also found to be small and the importance of these methods to nonlinear computation is discussed. Published version: Phys. Plasmas 24, 012504 (2017) [http://dx

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“…13 Consistent with experimental observations during the QH-mode, the simulation results using the NIMROD code illustrate that the particle transport is larger relative to the thermal transport in the QH-mode. 14 It has great realistic significance for the future fusion devices.…”

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confidence: 99%

Impact of E × B shear flow on low-n MHD instabilities

Chen

et al. 2017

Physics of Plasmas

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Recently, the stationary high confinement operations with improved pedestal conditions have been achieved in DIII-D [K. H. Burrell , Phys. Plasmas, 056103 (2016)], accompanying the spontaneous transition from the coherent edge harmonic oscillation (EHO) to the broadband MHD turbulence state by reducing the neutral beam injection torque to zero. It is highly significant for the burning plasma devices such as ITER. Simulations about the effects of × shear flow on the quiescent H-mode (QH-mode) are carried out using the three-field two-fluid model in the field-aligned coordinate under the BOUT++ framework. Using the shifted circular cross-section equilibriums including bootstrap current, the results demonstrate that the × shear flow strongly destabilizes low-n peeling modes, which are mainly driven by the gradient of parallel current in peeling-dominant cases and are sensitive to the shear. Adopting the much more general shape of × shear ([Formula: see text]) profiles, the linear and nonlinear BOUT++ simulations show qualitative consistence with the experiments. The stronger shear flow shifts the most unstable mode to lower-n and narrows the mode spectrum. At the meantime, the nonlinear simulations of the QH-mode indicate that the shear flow in both co- and counter directions of diamagnetic flow has some similar effects. The nonlinear mode interaction is enhanced during the mode amplitude saturation phase. These results reveal that the fundamental physics mechanism of the QH-mode may be shear flow and are significant for understanding the mechanism of EHO and QH-mode.

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NIMROD modeling of quiescent H-mode: reconstruction considerations and saturation mechanism

Cited by 13 publications

References 34 publications

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

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

Effect of scrape-off-layer current on reconstructed tokamak equilibrium

Impact of E × B shear flow on low-n MHD instabilities

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