Pedestal stability analysis on MAST in preparation for MAST-U

Knölker, M.; Osborne, T.H.; Belli, E. A.; Henderson, S.; Kirk, A.; Kogan, L. A.; Saarelma, S.; Snyder, P. B.

doi:10.1088/1741-4326/abe804

Cited by 6 publications

(10 citation statements)

References 50 publications

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“…The shots also have long periods of type I ELMs with a high amount (for MAST) of ELM cycles, such that ELM averaged profiles can be used. In both configurations the experimental point is located in the unstable region close to the ballooning boundary, consistent with [21]. Note that not all MAST type I ELMs are in this unstable region.…”

Section: Mast Elm Data For Europed Inputssupporting

confidence: 83%

“…In most MAST type I regimes, that are not mixed with type II ELMs, the experimental point is positioned on or close to the ballooning boundary [21]. As shown in section 4, the type I pedestal experimental point is usually at a lower current density than the P-B nose and is usually ballooning unstable.…”

Section: Analysis Of Type II Experimental Datamentioning

confidence: 98%

“…Europed is based on the EPED1 model [19], where the pedestal height and width can be predicted. EPED predictions have been obtained on various conventional tokamaks [20], and more recently predictions for MAST pedestals have been performed [21]. However, it is still important to analyse the MAST data to verify whether the Europed/EPED model assumptions are valid for MAST and spherical tokamaks in general.…”

Section: Introductionmentioning

confidence: 99%

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Pedestal analysis of MAST ELMy regimes

Smith

Kirk

Chapman-Oplopoiou

et al. 2022

Plasma Phys. Control. Fusion

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MAST pedestal data has been analysed, where a pedestal database of 892 shots was obtained, using the upgraded MAST Thomson Scattering (TS) diagnostic. Various ELM types are discussed, where characteristics and trends of MAST pedestals are shown. The data from the upgraded TS diagnostic confirms pedestal characteristics found in earlier analysis, using previous TS systems. Using the database, calculations of the bootstrap current are obtained using the different analytical formulae (Sauter and Redl), and comparisons are performed. The upgraded MAST TS system now spans the full plasma mid-plane, such that direct comparisons between inboard and outboard pedestals can be obtained, asymmetries in the density pedestal width were found. To increase confidence in spherical tokamak pedestal predictions, the assumptions of Europed have been validated from the MAST pedestal data, and a value for the KBM constraint (C ~ 0.145) has been obtained. The first spherical tokamak pedestal predictions were performed in Europed and compared to experimental values. Using C=0.145 the temperature pedestal height was predicted to within 10% of the experimental value. In addition type II ELMs on MAST are analysed, and stability analysis and parameter scans have been performed using ESSIVE. Similar MHD stability properties are observed for type I and type II ELMs, originating from the mixed ELM regimes, it is therefore difficult to distinguish these ELMs using the ideal MHD codes.

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Section: Mast Elm Data For Europed Inputssupporting

confidence: 83%

Section: Analysis Of Type II Experimental Datamentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Pedestal analysis of MAST ELMy regimes

Smith

Kirk

Chapman-Oplopoiou

et al. 2022

Plasma Phys. Control. Fusion

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“…The ion temperature is assumed equaled to electron temperature in this simulation. Note that the influence of ion vs electron temperature in the pedestal for linear stability is not significant, which has been shown by the reference [27] with ELITE.…”

Section: Equilibria For the East High-β P Long-pulse Experiments And ...mentioning

confidence: 66%

Characteristics of grassy ELMs and their impact on the divertor heat flux width

Li¹,

Xu²,

Wang³

et al. 2022

Nucl. Fusion

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BOUT++ turbulence simulations are conducted for a 60s steady-state long pulse high βp EAST grassy ELM discharge. BOUT++ linear simulations show that the unstable mode spectrum covers a range of toroidal mode numbers from low-n (n=10~15) peeling-ballooning modes (P-B) to high-n (n=40~80) drift-Alfvén instabilities. Nonlinear simulations show that the ELM crash is triggered by low-n peeling modes and fluctuation is generated at the peak pressure gradient position and radially spread outward into the Scrape-Off-Layer (SOL), even though the drift-Alfvén instabilities dominate the linear growth phase. However, drift-Alfvén turbulence delays the onset of the grassy ELM and enhances the energy loss with the fluctuation extending to pedestal top region. Simulations further show that if the peeling drive is removed, the fluctuation amplitude drops by an order of magnitude and the ELM crashes disappear. The divertor heat flux width is ~2 times larger than the estimates based on the HD model and the Eich’s ITPA multi-tokamak scaling (or empirical Eich scaling) due to the strong radial turbulence transport.

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“…However, it was found that in spherical tokamaks (STs) this model can be less reliable. While in past studies ELMing discharges in MAST have been found to be limited by ideal ballooning modes [9,10], this is not the case for NSTX. Here, ideal PB mode stability thresholds can be strongly underestimated, such that ELMing plasmas are predicted to sit deep inside the stable domain [11][12][13][14][15].…”

Section: Introductionmentioning

confidence: 85%

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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Pedestal stability analysis on MAST in preparation for MAST-U

Cited by 6 publications

References 50 publications

Pedestal analysis of MAST ELMy regimes

Pedestal analysis of MAST ELMy regimes

Characteristics of grassy ELMs and their impact on the divertor heat flux width

Critical role of current-driven instabilities for ELMs in NSTX

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