Evolution of the pedestal on MAST and the implications for ELM power loadings

Kirk, A.; Counsell, G.; Cunningham, G.; Dowling, J.; Dunstan, M. R.; Meyer, H.; Price, M.; Saarelma, S.; Scannell, R.; Walsh, M. J.; Wilson, H. R.; Team, the MAST

doi:10.1088/0741-3335/49/8/011

Cited by 70 publications

(121 citation statements)

References 22 publications

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“…A picture of multiple filaments released in the midplane region during the ELM evolution, as seen elsewhere (e.g. AUG [2], MAST [8]) is therefore also consistent with these early TCV observations.…”

Section: Elm Filamentssupporting

confidence: 87%

“…Several distinct filaments can be seen with almost purely toroidal inclination above the main band of emission at the strike point. Such patterns can be qualitatively reproduced by field line tracing calculations following the approach in [2,8]. Assuming: (1) a filament release point in the outboard midplane SOL, (2) that the pre-ELM magnetic field structure is not disturbed by the filament [9] and (3) that there is no significant poloidal rotation of the filament, then the equilibrium reconstruction can be used to trace field lines from the point of origin to the divertor targets.…”

Section: Elm Filamentsmentioning

confidence: 99%

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ELM induced divertor heat loads on TCV

Márki

Pitts

Horáček

et al. 2009

Journal of Nuclear Materials

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a b s t r a c tResults are presented for heat loads at the TCV outer divertor target during ELMing H-mode using a fast IR camera. Benefitting from a recent surface cleaning of the entire first wall graphite armour, a comparison of the transient thermal response of freshly cleaned and untreated tile surfaces (coated with thick codeposited layers) has been performed. The latter routinely exhibit temperature transients exceeding those of the clean ones by a factor $3, even if co-deposition throughout the first days of operation following the cleaning process leads to the steady regrowth of thin layers. Filaments are occasionally observed during the ELM heat flux rise phase, showing a spatial structure consistent with energy release at discrete toroidal locations in the outer midplane vicinity and with individual filaments carrying $1% of the total ELM energy. The temporal waveform of the ELM heat load is found to be in good agreement with the collisionless free streaming particle model.

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Section: Elm Filamentssupporting

confidence: 87%

Section: Elm Filamentsmentioning

confidence: 99%

ELM induced divertor heat loads on TCV

Márki

Pitts

Horáček

et al. 2009

Journal of Nuclear Materials

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“…2. In MAST, images of the global topology of emission filaments observed during an ELM [8] are consistent with the helical structure produced by a homoclinic tangle. This can be seen by extending the lobes of the tangle shown in Fig.…”

Section: Supporting Experimental Observationssupporting

confidence: 56%

A conceptual model of the magnetic topology and nonlinear dynamics of ELMs

Evans

Jakubowski

et al. 2009

Journal of Nuclear Materials

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A conceptual model is introduced describing the 3D magnetic topology and nonlinear evolution of Type-I edge localized modes (ELMs), which immediately follows the initial linear peeling-ballooning growth phase. The model requires the feedback amplification of stable and unstable invariant manifolds that increases the helical perturbation. The amplification process is caused by the rapid growth of field-aligned helical thermoelectric currents that flow through relatively short pedestal plasma flux tubes connecting the inner and outer divertor target plates. It is shown that the model qualitatively agrees with the formation of global field-aligned emission filaments and with fast IR heat flux splitting patterns of the inner and outer strike points observed experimentally. In addition, the model predicts an increase in the size of the ELMs as the pedestal collisionality drops. Experimental data and modeling results are presented supporting the basic conceptual elements of the model.

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“…the width and height, and pedestal dynamics are quantified by least squares mtanh fits to ELM synchronised HRTS profiles. Fitting an mtanh function to radial kinetic profiles is a common technique used on many machines such as JET [19,20], AUG [23,26], DIII-D [22,27], Alcator C-Mod [45,46], MAST [24,28,29,47], NSTX [25] and JT-60 [48]. The mtanh fits to the JET HRTS profiles presented in this section are used in Section 5 when evaluating the Peeling Ballooning stability and comparing experimental results to EPED1 predictions for the pedestal pressure.…”

Section: Pedestal Measurementsmentioning

confidence: 99%

Pedestal study across a deuterium fuelling scan for highδELMy H-mode plasmas on JET with the carbon wall

Leyland¹,

Beurskens²,

Frassinetti³

et al. 2013

Nucl. Fusion

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We present the results from a new fuelling scan database consisting of 14 high triangularity ( ~ 0.41), Type I ELMy H-mode JET plasmas. As the fuelling level is increased from low, ( D ~ 0.2x10 22 el/s, n e,ped /n gw =0.7), to high dosing ( D ~ 2.6x10 22 el/s, n e,ped /n gw =1.0) the variation in ELM behaviour is consistent with a transition from 'pure Type I' to 'mixed Type I/II' ELMs [1]. However, the pulses in Scattering (HRTS) system. We continue by presenting, for the first time, the role of pedestal structure, as quantified by a least squares mtanh fit to the HRTS profiles, on the performance across the fuelling scan. A key result is that the pedestal width narrows and peak pressure gradient increases during the ELM cycle for low fuelling plasmas, whereas at high fuelling the pedestal width and peak pressure gradient saturates towards the latter half of the ELM cycle. An ideal MHD stability analysis shows that both low and high fuelling plasmas move from stable to unstable approaching the ideal ballooning limit of the finite peeling ballooning stability boundary. Comparison to EPED predictions show on average good agreement with experimental measurements for both pedestal height and width however when presented as a function of pedestal density, experiment and model show opposing trends. The measured pre-ELM pressure pedestal height increases by ~ 20% whereas EPED predicts a decrease of 25% from low to high fuelling. Similarly the measured pressure pedestal width widens by ~ 55%, in poloidal flux space, whereas EPED predicts a decrease of 20% from low to high fuelling. We give two possible explanations for the disagreement. First, it may be that EPED under-predicts the critical density, which marks the transition from kink-peeling to ballooning limited plasmas. Second, the stronger broadening of the experimental pedestal width than predicted by EPED is an indication that other transport related processes contribute to defining the pedestal width such as enhanced inter-ELM transport as observed at high fuelling, for mixed Type I/II ELMy pulses.M. Leyland

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Evolution of the pedestal on MAST and the implications for ELM power loadings

Cited by 70 publications

References 22 publications

ELM induced divertor heat loads on TCV

ELM induced divertor heat loads on TCV

A conceptual model of the magnetic topology and nonlinear dynamics of ELMs

Pedestal study across a deuterium fuelling scan for highδELMy H-mode plasmas on JET with the carbon wall

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