Free boundary 3D ideal MHD equilibrium calculations for non-linearly saturated current driven external kink modes in tokamaks

Kleiner, Andreas; Graves, J. P.; Cooper, W. A.; Nicolas, T; Wahlberg, Christer

doi:10.1088/1741-4326/aac607

Cited by 9 publications

(17 citation statements)

References 20 publications

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“…Our collaboration has investigated the QH-mode both numerically and analytically. We have used the VMEC code to find saturated nonlinear MHD states [15]. These can be found in two regimes.…”

Section: Recent Work On Reactor Relevant Pedestalsmentioning

confidence: 99%

“…Candidate modes which may explain the QH-mode are investigated using the VMEC [41] non-axisymmetric equilibrium code and the linear ballooning stability code COBRAVMEC [42,43]. Previous work has investigated how such a saturated MHD mode may appear at the plasma edge [15]. It has been shown that such a mode can appear due to the q profile being just below a rational value at the plasma edge.…”

Section: Vmec Equilibrium Modellingmentioning

confidence: 99%

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Towards understanding reactor relevant tokamak pedestals

et al. 2021

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The physics of the tokamak pedestal is still not fully understood, for example there is no fully predictive model for the pedestal height and width. However, the pedestal is key in determining the fusion power for a given scenario. If we can improve our understanding of reactor relevant pedestals we will improve our confidence in designing potential fusion power plants. Work has been carried out as part of a collaboration on reactor relevant pedestal physics. We report some of the results in detail here and review some of the wider work which will be reported in full elsewhere. First, we attempt to use a gyrokinetic-based calculation to eliminate the pedestal top density as a model input for Europed/EPED pedestal predictions. We assume power balance at the top of the pedestal, that is, the heat flux crossing the separatrix must be equal to the heat source at the top of the pedestal and investigate the consequences of this assumption. Unfortunately, this method was not successful. Second, we investigate the effects of non flux surface density on the bootstrap current. Third, type I ELMs will not be tolerable for a reactor relevant regime due to the damage that they are expected to cause to plasma facing components. In recent years various methods of running tokamak plasmas without large ELMs have been developed. These include small and no ELM regimes, the use of resonant magnetic perturbations and the use of vertical kicks. We discuss the quiescent H-mode here. Finally we give a summary and directions for future work.

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Section: Recent Work On Reactor Relevant Pedestalsmentioning

confidence: 99%

Section: Vmec Equilibrium Modellingmentioning

confidence: 99%

Towards understanding reactor relevant tokamak pedestals

et al. 2021

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“…Recent experimental findings point to the E × B shearing rate as the key ingredient for the development of the characteristics of these oscillations [19]. Indeed numerical investigations of QH-mode DIII-D plasma discharges with sheared E×B flows showed that low-n modes are linearly dominant and are eventually sustained in the nonlinear stage at moderately low amplitude [7,[20][21][22][23][24].…”

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confidence: 99%

Excitation Mechanism of Low- n Edge Harmonic Oscillations in Edge Localized Mode-Free, High Performance, Tokamak Plasmas

et al. 2019

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The excitation mechanism for low-n Edge Harmonic Oscillations in quiescent H-mode regimes is identified analytically. We show that the combined effect of diamagnetic and poloidal MHD flows, with the constraint of a Doppler-like effect of the ion flow, leads to the stabilisation of short wavelength modes, allowing lown perturbation to grow. The analysis, performed in tokamak toroidal geometry, includes the effects of large edge pressure gradients, associated with the local flattening of the safety factor and diamagnetic flows, sheared parallel and E × B rotation and a vacuum region between plasma and the ideal metallic wall. The separatrix also is modelled analytically.

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“…While the characteristics of modes on the ballooning side in the NSTX discharges is very similar to ballooning modes in the known large aspect ratio cases, we will now focus on the difference of resistive PB modes in NSTX compared with the well known ideal peeling modes. Typical ideal kink-peeling modes in large aspect ratio have low toroidal mode number n and a rather narrow poloidal spectrum in straight field line coordinates as the perturbation wraps around the poloidal circumference [41,42]. To compare the properties of kink-peeling modes in NSTX and DIII-D, we choose DIII-D discharge 147105.…”

Section: Analysis Of Mode Eigenfunctionsmentioning

confidence: 99%

Critical role of current-driven instabilities for ELMs in NSTX

Kleiner¹,

Ferraro²,

Canal³

et al. 2022

Nucl. Fusion

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The impact of different extended-magnetohydrodynamic (MHD) contributions on the stability thresholds of peeling-ballooning modes in ELMing and ELM-free plasmas in the spherical tokamak NSTX is investigated with the initial value code M3D-C1. We show that ELMing discharges in NSTX are limited by resistive current-driven peeling modes, whereas non-ELMing wide-pedestal H-mode discharges are located near the ideal pressure-driven ballooning threshold. It is demonstrated that extended-MHD can lead to more reliable edge stability predictions than existing ideal-MHD models. Resistive peeling-ballooning modes are found to exist well before the ideal stability threshold is met, and kink-peeling modes exhibit considerable sensitivity to plasma resistivity. Other effects not considered in ideal-MHD models affect PB modes in NSTX in a weaker way. Gyroviscous stress appears stabilizing such that the stability boundary lies closer to the experimental point. Equilibrium rotation can suppress ideal core modes and thus isolate edge modes. These results are important for the development of a predictive pedestal model for low-aspect ratio tokamaks.

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Free boundary 3D ideal MHD equilibrium calculations for non-linearly saturated current driven external kink modes in tokamaks

Cited by 9 publications

References 20 publications

Towards understanding reactor relevant tokamak pedestals

Towards understanding reactor relevant tokamak pedestals

Excitation Mechanism of Low- n Edge Harmonic Oscillations in Edge Localized Mode-Free, High Performance, Tokamak Plasmas

Critical role of current-driven instabilities for ELMs in NSTX

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