H-mode results in ASDEX Upgrade

Ryter, F.; Büchl, K.; Fuchs, C.; Gehre, O.; Gruber, O.; Herrmann, A.; Kallenbach, A.; Kaufmann, Michael; Köppendörfer, W.; Mast, F.; Mertens, V.; Neu, R.; Hempel, S. De Pena; Steuer, K.-H.; Zohm, H.

doi:10.1088/0741-3335/36/7a/011

Cited by 55 publications

(46 citation statements)

References 7 publications

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“…While the ELM-free H-modes appear to fit the ASDEX-Upgrade H-mode power threshold scaling, the ELMy H-modes following lithium pellet injection occur at significantly lower input power. These results, together with previous results from other tokamaks [3][4][5], suggest that if the neB dependence of the H-mode power threshold is approximately correct, then there is also a dependence on wall conditions that can significantly lower the power threshold. Fig.…”

supporting

confidence: 75%

“…Therefore, it is possible that S should be replaced with R 2 . 5 or that the power law dependences of ne or BT are not exactly linear. Further experiments including additional heating with ICRF and direct comparisons with ASDEX-Upgrade will be performed to test this scaling in detail.…”

mentioning

confidence: 99%

“…On several tokamaks, through extensive wall conditioning techniques to reduce impurity influxes, H-modes have also been achieved with ohmic power alone up to BT 5 2.1 T and ne 8 x 1019 m-3 [3][4][5]. The threshold input power necessary to achieve H-mode was found to increase with increasing toroidal field [2-6] and electron density [4,5], which led to the conclusion that high field, high density tokamaks would find it difficult or impossible to operate in the H-mode [7]. The initial results from Alcator CMod [8] show that ohmic H-modes can be achieved at toroidal fields at least as high as BT = 5.25 T and line averaged densities up to 1.4 x 1020 m-3 with all molybdenum plasma facing components.…”

mentioning

confidence: 99%

“…If plasma physics alone governs the transition, then P/(neBrR 2 . 5 ) is a scale invariant parameter [12,13]. Therefore, it is possible that S should be replaced with R 2 .…”

mentioning

confidence: 99%

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First ohmic H modes in ALCATOR C-MOD

et al. 1994

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Ohmic H modes have been achieved in ALCATOR C-MOD with toroidal fields up to BT ≈ 5.25 T and line averaged densities up to ne ≈ 1.4 × 1020 m-3 with less than 1 MW of input power. In ELM-free cases at lower toroidal fields, the energy confinement increases by at least 60% and the particle confinement increases by more than a factor of two. The ELM-free H modes appear to fit the threshold power scaling observed on other tokamaks, P/S (MW/m2)=4.4 × 10-3 neBT (1019 m-3.T), up to power densities of about 0.15 MW/m2. At higher toroidal fields, ELMy H modes were observed after the injection of lithium pellets at about half of the scaled threshold power density. All of these results were obtained with molybdenum plasma facing components and the ELM-free H modes were obtained without boronization or other wall coatings

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supporting

confidence: 75%

mentioning

confidence: 99%

mentioning

confidence: 99%

“…If plasma physics alone governs the transition, then P/(neBrR 2 . 5 ) is a scale invariant parameter [12,13]. Therefore, it is possible that S should be replaced with R 2 .…”

mentioning

confidence: 99%

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First ohmic H modes in ALCATOR C-MOD

et al. 1994

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“…Summarizing, the L-H and H-L power thresholds exhibit very similar dependences and the hysteresis often does not appear clearly which is mainly caused by the rather large radiation fraction which develops during the H-mode. This contribution is significantly higher with the tungsten wall, the hysteresis was clearer in the carbon wall [47]. The investigation of the hysteresis at the H-L transition is not the only aspect of this topic which can be extended by the study of the comparison between P loss and P scal during the development of the H-mode after the L-H transition.…”

Section: Survey Of the H-mode Power Threshold And Transition Physics mentioning

confidence: 99%

Survey of the H-mode power threshold and transition physics studies in ASDEX Upgrade

et al. 2013

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Abstract. An overview of the H-mode threshold power in ASDEX Upgrade which addresses the impact of the tungsten versus graphite wall, the dependences upon plasma current and density, as well as the influence of the plasma ion mass is given. Results on the H-L back transition are also presented. Dedicated L-H transition studies with electron heating at low density, which enable a complete separation of the electron and ion channels, reveal that the ion heat flux is a key parameter in the L-H transition physics mechanism through the main ion pressure gradient which is itself the main contribution to the radial electric field and the induced flow shearing at the edge. The electron channel does not play any role. The 3D magnetic field perturbations used to mitigate the ELMs are found to also influence the L-H transition and to increase the power threshold. This effect is caused by a flattening of the edge pressure gradient in the presence of the 3D fields such that the L-H transitions with and without perturbations occur at the same value of the radial electric field well, but at different heating powers.

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Understanding of Hysteresis Behaviors at the L‐H‐L Transitions in Tokamak Plasma Based on Bifurcation Concept

Chatthong

Onjun

2016

Contrib. Plasma Phys.

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The hysteresis behaviour at the L-H-L transitions in tokamak plasma is investigated based on bifurcation concept. The formation of an edge transport barrier (ETB) is modeled via thermal and particle transport equations with the flow shear suppression effect on anomalous transport included. The anomalous transport is modeled based on critical gradients threshold and the flow shear is calculated from the force balance equation, couples the two transport equations leading to a non-linear behaviour. Analytical investigation reveals that the fluxes versus gradients space exhibits bifurcation behaviour with s-curve soft bifurcation type. Apparently, the backward H-L transition occurs at lower values than that of the forward L-H transition, illustrating hysteresis behaviour. The hysteresis properties, i.e. locations of threshold fluxes, gradients and their ratios are analyzed as a function of neoclassical and anomalous transport values and critical gradients. It is found that the minimum heat flux for maintaining H-mode depends on several plasma parameters including the strength of anomalous transport and neoclassical transport. In particular, the hysteresis depth becomes larger when neoclassical transport decreases or anomalous transport increases.

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H-mode results in ASDEX Upgrade

Cited by 55 publications

References 7 publications

First ohmic H modes in ALCATOR C-MOD

First ohmic H modes in ALCATOR C-MOD

Survey of the H-mode power threshold and transition physics studies in ASDEX Upgrade

Understanding of Hysteresis Behaviors at the L‐H‐L Transitions in Tokamak Plasma Based on Bifurcation Concept

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