Limits to the H-mode pedestal pressure gradient in DIII-D

Groebner, R. J.; Snyder, P. B.; Osborne, T. H.; Leonard, A. W.; Rhodes, T. L.; Zeng, L.; Unterberg, E.A.; Yan, Z.; McKee, G. R.; Lasnier, C.J.; Boedo, J.A.; Watkins, J.G.

doi:10.1088/0029-5515/50/6/064002

Cited by 38 publications

(61 citation statements)

References 32 publications

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“…For this purpose, time windows with constant plasma parameters have been selected from a series of reproducible shots. The results show similar trends to those observed on AUG 11 and DIII-D 35,45 . In particular, they indicate that the pedestal pressure gradient may saturate shortly before the ELM onset.…”

Section: Discussionsupporting

confidence: 84%

Electron temperature and density profile evolution during the edge-localized mode cycle in ohmic and electron cyclotron-heated H-mode plasmas in TCV

Pitzschke

Behn

Sauter

et al. 2011

Plasma Phys. Control. Fusion

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The dynamics of electron temperature and density profiles during quasi-stationary H-mode phases in the TCV tokamak has been investigated for type III and type I ELMs using electron cyclotron heating (ECH) to vary the collisionality. At heating power levels close to the threshold for the L-H transition, ELMs of type III were observed, with an energy loss per ELM below 10% of the total plasma energy. Electron temperature and pressure showed no significant increase during the phase before the ELM crash. ELMs of type I were characterized by a lower repetition rate, but caused fractional energy losses reaching 20%. For this ELM type, a clear increase in pedestal pressure and pressure gradient was observed before the collapse associated with the ELM event. The rapid drop in electron temperature also affected the plasma core explaining the rather large energy losses per ELM. Ideal MHD stability calculations of the edge pedestal with the KINX code showed that high-n ballooning modes restricted the achievable pressure gradient at high collisionality and ELMs of type III. With additional heating and type I ELMs, stability limits were set by medium-n kink-ballooning modes. Comparing the values of the pressure gradients and current densities obtained from experimental data with those of ideal MHD stability calculations showed good agreement. The model, however, needs to account for the radial displacement of the location of maximum pressure gradient during the ELM cycle.

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Section: Discussionsupporting

confidence: 84%

Electron temperature and density profile evolution during the edge-localized mode cycle in ohmic and electron cyclotron-heated H-mode plasmas in TCV

Pitzschke

Behn

Sauter

et al. 2011

Plasma Phys. Control. Fusion

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“…For the pedestal height to increase when limited by KB modes the pedestal must widen so as not to exceed the critical pressure gradient. This behaviour is typically observed on DIII-D [27,51], and MAST [28,29] throughout the ELM cycle which suggests the pressure gradient is limited by KB modes early on in the ELM cycle. In contrast, the observation that the JET pedestal width becomes narrower during the ELM cycle for the low fuelling pulse (and for the high fuelling pulse in the initial phase of the ELM cycle) suggests that the pressure gradient may not approach KB mode criticality until the latter part of the ELM cycle.…”

Section: Discussionmentioning

confidence: 77%

“…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%

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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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“…In the recent years a lot of effort was focused on documenting and understanding the basic properties of the pedestal -its gradients [2,4,5], widths [6][7][8][9][10][11][12] and top values [13][14][15]. This paper focuses on the pedestal characteristics, in particular the gradients, just before the onset of an edge localized mode (ELM) in type-I ELMy H-modes.…”

Section: Introductionmentioning

confidence: 99%

Analysis of temperature and density pedestal gradients in AUG, DIII-D and JET

et al. 2013

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Abstract:A comparison of the AUG and DIII-D temperature pedestals showed significant differences between electrons and ions. For high collision rates the ions are coupled to the electrons and show very similar pedestal top values and gradients. For lower collision rates both decouple and the ion pedestal becomes less steep. The electron temperature gradient scales linearly with its pedestal top value. This trend is independent of collisionality and plasma shape. The normalized total pressure gradient α shows strong correlations with the plasma shape in a way expected by peeling-ballooning theory. The different behaviours of the electron temperature gradient only and the total pedestal pressure gradient suggests a limit for the electron temperature pedestal different from linear edge MHD stability.

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Limits to the H-mode pedestal pressure gradient in DIII-D

Abstract: This is a preprint of a paper to be presented at the 12th International Workshop on H-Mode Physics and Transport Barriers, September 30 Through October 2, 2009, in Princeton, New Jersey, and to be published in a special issue of Nuclear Fusion.

Cited by 38 publications

References 32 publications

Electron temperature and density profile evolution during the edge-localized mode cycle in ohmic and electron cyclotron-heated H-mode plasmas in TCV

Electron temperature and density profile evolution during the edge-localized mode cycle in ohmic and electron cyclotron-heated H-mode plasmas in TCV

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

Analysis of temperature and density pedestal gradients in AUG, DIII-D and JET

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