H-mode threshold and confinement in helium and deuterium in ASDEX Upgrade

Ryter, F.; Pütterich, T.; Reich, M.; Scarabosio, A.; Wolfrum, E.; Fischer, R.; Adamov, M. Gemisic; Hicks, N.; Kurzan, B.; Maggi, C. F.; Neu, R.; Rohde, V.; Tardini, G.

doi:10.1088/0029-5515/49/6/062003

Cited by 104 publications

(174 citation statements)

References 13 publications

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“…They revealed that the threshold was about 25% lower than previous data and therefore also below the scaling by the same amount, [14]. This has been confirmed during the following campaigns 2011-2013.…”

Section: Transition From Graphite To Tungsten Wallsupporting

confidence: 66%

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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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Section: Transition From Graphite To Tungsten Wallsupporting

confidence: 66%

“…[1] and references therein, and has been the subject of recent studies [45,14,46]. The threshold exhibits a minimum atn e,min which separates the so-called low and high density branches.…”

Section: L-h and H-l Power Thresholdsmentioning

confidence: 99%

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

et al. 2013

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“…Multiplying these values by the minor radius gives an apparent poloidal rotation velocity of 1.4 km s −1 . 17 Sets of filaments regularly appear within a short time interval as shown in figure 17(b). Here, the average mapping target angles at the time of the highest intensity for the four most intense structures are highlighted by dashed lines.…”

Section: Correlation Of Smps To Elm Filamentsmentioning

confidence: 96%

“…While increasing (decreasing) the input power in this discharge the ELM frequency increases (decreases). In addition, during the investigated phase the discharge is heated with 7.5 MW by neutral beam injection, which is significantly further above the typical LH threshold for the parameters of this discharge (P LH ∼ 1.6 MW [17]). This is also higher than the range, in which type III ELMs are usually observed.…”

Section: Quantification and Scaling Of Solitarinessmentioning

confidence: 98%

Solitary magnetic perturbations at the ELM onset

et al. 2012

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Tokamak H-mode plasmas frequently exhibit edge-localized modes (ELMs). ELMs allow maintaining sufficient plasma purity and thus enable stationary H-mode. On the other hand in a future device ELMs may cause divertor power flux densities far in excess of tolerable material limits. The size of the energy loss per ELM is determined by saturation effects in the non-linear phase of the ELM, which at present is hardly understood. ASDEX Upgrade is now equipped with a set of fast sampling diagnostics, which is well suited to investigate the chain of events around the ELM crash with appropriate temporal resolution ( 10 µs).Solitary magnetic perturbations (SMPs) are identified as dominant features in the radial magnetic fluctuations below 100 kHz. They are typically observed close (±100 µs) to the onset of pedestal erosion. SMPs are field aligned structures rotating in the electron diamagnetic drift direction with perpendicular velocities of about 10 km s −1 . A comparison of perpendicular velocities suggests that the perturbation evoking SMPs is located at or inside the separatrix. Analysis of very pronounced examples showed that the number of peaks per toroidal turn is 1 or 2, which is clearly lower than the corresponding numbers in linear stability calculations. In combination with strong peaking of the magnetic signals this results in a solitary appearance resembling modes like palm tree modes, edge snakes or outer modes. This behaviour has been quantified as solitariness and correlated with main plasma parameters.SMPs may be considered as a signature of the non-linear ELM phase originating at the separatrix or further inside. Thus they provide a handle to investigate the transition from linear to non-linear ELM phase. By comparison with data from gas puff imaging processes in the non-linear phase at or inside the separatrix and in the scrape-off layer (SOL) can be correlated. A connection between the passing of an SMP and the onset of radial filament propagation has been found. Eventually the findings related to SMPs may contribute to a future quantitative understanding of the non-linear ELM evolution.

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“…One rationale for this case is that it could be important for obtaining H-mode in the pre-activation phase, especially if the H-mode cannot be achieved in bulk hydrogen. Scalings for the L→H power threshold in He 4 plasmas are controversial, but some tokamaks report lower H-mode threshold in He 4 than in H [11]. The predictions achieve H-mode with extrapolations of database results for P LH [12].…”

Section: Benchmark Casesmentioning

confidence: 79%

Benchmarking ICRF Full-wave Solvers for ITER

2011

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Benchmarking of full-wave solvers for ICRF simulations is performed using plasma profiles and equilibria obtained from integrated self-consistent modeling predictions of four ITER plasmas. One is for a high performance baseline (5.3 T, 15 MA) DT H-mode. The others are for half-field, half-current plasmas of interest for the pre-activation phase with bulk plasma ion species being either hydrogen or He 4 . The predicted profiles are used by six full-wave solver groups to simulate the ICRF electromagnetic fields and heating, and by three of these groups to simulate the current-drive.Approximate agreement is achieved for the predicted heating power for the DT and He 4 cases. Factor of two disagreements are found for the cases with second harmonic He 3 heating in bulk H cases. Approximate agreement is achieved simulating the ICRF current drive.

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H-mode threshold and confinement in helium and deuterium in ASDEX Upgrade

Cited by 104 publications

References 13 publications

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

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

Solitary magnetic perturbations at the ELM onset

Benchmarking ICRF Full-wave Solvers for ITER

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