Structure and dynamics of spontaneous and induced ELMs on ASDEX Upgrade

Neuhäuser, J.; Bobkov, V.; Chankin, A.; Coster, D.; Dux, R.; Eich, T.; Fattorini, L.; García-Muñoz, M.; Harhausen, J.; Herrmann, A.; Horton, L. D.; Kallenbach, A.; Kálvin, S.; Kirk, A.; Koch, B.; Kocsis, G.; Kurzan, B.; Lang, P. T.; Maraschek, M.; Müller, Hans; Mürmann, H.; Neu, R.; Reich, M.; Rohde, V.; Schmid, Andreas K.; Suttrop, W.; Tsalas, M.; Wischmeier, M.; Wolfrum, E.

doi:10.1088/0029-5515/48/4/045005

Cited by 32 publications

(39 citation statements)

References 46 publications

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“…At this point, fast parallel transport along these homoclinic flux tubes causes a rapid increase in the electron temperature (T e ) inside the magnetic footprints near the wall and divertor surfaces. Experimental measurements taken during the early growth of an ELM demonstrate that there is a rapid release of thermal energy from the area located near the steep gradient region leading up to the top of the pedestal just inside the separatrix (Kirk et al, 2007, Neuhauser et al, 2008. These observations are consistent with our requirement of a rapid increase in the radial energy transport during this time.…”

Section: Description Of the Temporal Evolution Prescribed By The Modelsupporting

confidence: 86%

“…These observations are consistent with our requirement of a rapid increase in the radial energy transport during this time. These rapid bursts of energy flowing from the pedestal into the divertor appear to be correlated with an increase in broadband magnetic fluctuations in the pedestal starting about 10 μs before the onset of the nonlinear growth phase (Neuhauser et al, 2008) suggesting that currents in this region may play a key role in the onset of the nonlinear growth phase. In our model, it is these inital heat pulses associated with the linearly growing MHD instability that provide the mechanism needed to form a feedback amplification loop.…”

Section: Description Of the Temporal Evolution Prescribed By The Modelmentioning

confidence: 92%

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A Conceptual Model for the Nonlinear Dynamics of Edge-localized Modes in Tokamak Plasmas

Evans¹,

Wingen²,

Watkins³

et al. 2010

Nonlinear Dynamics

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Section: Description Of the Temporal Evolution Prescribed By The Modelsupporting

confidence: 86%

Section: Description Of the Temporal Evolution Prescribed By The Modelmentioning

confidence: 92%

A Conceptual Model for the Nonlinear Dynamics of Edge-localized Modes in Tokamak Plasmas

Evans¹,

Wingen²,

Watkins³

et al. 2010

Nonlinear Dynamics

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“…This suggests that the structures evoking SMPs, alone or in combination with another deviation from the equilibrium, provide conditions under which radiation filaments can propagate radially. Results guiding in a similar direction are reported in [24], where data measured by magnetic probes and Langmuir probes from ASDEX Upgrade are analysed. Here, an example of an ELM is presented ( figure 6) for which magnetic perturbations pass a combined Langmuir/magnetics probe mostly at times when peaks of the ion saturation current are registered.…”

Section: Summary and Discussionmentioning

confidence: 69%

“…In [21,24] single peaks of time integrated components of dB/dt have been followed in this direction.…”

Section: Parallel Structure and Dynamics Of Smpsmentioning

confidence: 99%

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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“…Perturbations of the poloidal and radial magnetic field during ELMs significantly exceeding the inter-ELM level are regularly observed in tokamak H-mode discharges [6,7,8,9]. Figure 2(a) illustrates a set of subsequent ELMs in discharge 42062.…”

Section: Magnetic Perturbations During Elmsmentioning

confidence: 99%

Non-linear magnetic perturbations during edge-localized modes in TCV dominated by lownmode components

et al. 2013

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Abstract. Edge localized modes (ELMs) are instabilities in the edge of tokamak plasmas in the high confinement regime (H-mode). Despite beneficial aspects of ELMs, in a future device the size of the energy loss per ELM must be controlled, in order to avoid intolerable divertor power flux densities. To proceed in understanding how the ELM size is determined and how ELM mitigation methods work it is necessary to characterize the non-linear evolution of ELMs.This publication presents a detailed analysis of the toroidal structure of dominant magnetic perturbations during type I ELMs in TCV. These signatures of the instability can be observed most intensely in close temporal vicinity to the onset of enhanced D α -radiation. In particular it is shown that dominant magnetic perturbations already have a rigid toroidal mode structure when they are detected with magnetic probes. This indicates that perturbations associated with this type of ELMs at TCV can not be observed in their linear phase. Furthermore it is demonstrated that the toroidal structure of dominant magnetic perturbations is most often dominated by the n = 1 component. This is in clear contrast to typical results of linear stability calculations, leading to the hypothesis that the dominant toroidal mode number from the linear to the non-linear phase has a transition from intermediate to low values. In general, the reported results show that non-linear coupling leads to a significant modification of the mode structure.

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Structure and dynamics of spontaneous and induced ELMs on ASDEX Upgrade

Cited by 32 publications

References 46 publications

A Conceptual Model for the Nonlinear Dynamics of Edge-localized Modes in Tokamak Plasmas

A Conceptual Model for the Nonlinear Dynamics of Edge-localized Modes in Tokamak Plasmas

Solitary magnetic perturbations at the ELM onset

Non-linear magnetic perturbations during edge-localized modes in TCV dominated by lownmode components

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