The impact of collisionality, FLR, and parallel closure effects on instabilities in the tokamak pedestal: Numerical studies with the NIMROD code

King, Jacob; Pankin, A.Y.; Kruger, Scott; Snyder, P. B.

doi:10.1063/1.4954302

Cited by 20 publications

(26 citation statements)

References 47 publications

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“…For purely resistive MHD model without inclusion of 2-fluid effects, the increase in resistivity always destabilizes all range of the edge localized modes. This contrasts to the recent study using NIMROD where the resistive stabilizing effects on low-n edge localized modes appear in both the single-fluid and the two-fluid MHD models[24] which might be arising from different resistivity model used in ideal and resistive limit. Our results also differs from resisitive effect studies on peeling-ballooning modes in other codes as M3D-C 1 (in single fluid limit[26]) and BOUT++ (in 2-fluid limit with constant resistivity profile[27]).…”

contrasting

confidence: 89%

Stabilizing effects of enhanced resistivity due to lithium-conditioning on low-n edge localized modes in NSTX

2017

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The stabilizing effects of enhanced edge resistivity on the low-n edge localized modes (ELMs) are reported for the first time in the context of ELM suppression in H-mode discharge due to lithium-conditioning in the National Spherical Torus Experiment (NSTX). Here n is the toroidal mode number. Linear stability analysis of the corresponding experimental equilibrium suggests that the change in the equilibrium plasma density profile alone due to lithium-conditioning may be insufficient for a complete suppression of ELMs. The enhanced resistivity due to the increased effective electric charge number Z eff after lithium-conditioning can account for additional stabilization effects that contribute to robust ELM suppression. Remarkably, such a stabilizing effect of enhanced edge resistivity on the low-n ELMs only exists when two-fluid effects are considered in the MHD model.

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confidence: 89%

Stabilizing effects of enhanced resistivity due to lithium-conditioning on low-n edge localized modes in NSTX

2017

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“…It is also the peak location of the edge To check the generality of our findings, we turn to the full extended MHD model including two-fluid and finite-Larmor-radius (FLR) effects. For the static equilibriums, the increased density appears to be destabilize to high-n modes, which was also previously reported in [46].…”

supporting

confidence: 83%

Enhanced toroidal flow stabilization of edge localized modes with increased plasma density

2017

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Toroidal flow alone is generally thought to have important influence on tokamak edge pedestal stability, even though theory analysis often predicts merely a weak stabilizing effect of toroidal flow on the edge localized modes (ELMs) in experimental parameter regimes. For the first time, we find from two-fluid MHD calculations that such a stabilization, however, can be significantly enhanced by increasing the edge plasma density. Our finding resolves a long-standing mystery whether or how toroidal rotation can indeed have effective influence on ELMs, and explains why the ELM mitigation and suppression by toroidal rotation are more favorably achieved in higher collisionality regime in recent experiments. The finding suggests a new control scheme on modulating toroidal flow stabilization of ELMs with plasma density, along with a new additional constraint on the optimal level of plasma density for the desired edge plasma conditions.

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“…Ref. [27][28][29]), which are known to modify the frequency through the mediation of the perturbations by both the ion and electron fluids are required to produce dynamics with a more representative frequency. The ion and electron fluids rotate in opposing directions for this discharge.…”

Section: Transport Analysismentioning

confidence: 99%

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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The impact of collisionality, FLR, and parallel closure effects on instabilities in the tokamak pedestal: Numerical studies with the NIMROD code

Cited by 20 publications

References 47 publications

Stabilizing effects of enhanced resistivity due to lithium-conditioning on low-n edge localized modes in NSTX

Stabilizing effects of enhanced resistivity due to lithium-conditioning on low-n edge localized modes in NSTX

Enhanced toroidal flow stabilization of edge localized modes with increased plasma density

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

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