Characterization and interpretation of the Edge Snake in between type-I edge localized modes at ASDEX Upgrade

Sommer, Fabian; Günter, S.; Kallenbach, A.; Maraschek, M.; Boom, J.; Fischer, R.; Hicks, N.; Luhmann, N. C.; Park, H. K.; Reiter, B.; Wenninger, R.; Wolfrum, E.

doi:10.1088/0741-3335/53/8/085012

Cited by 7 publications

(13 citation statements)

References 15 publications

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“…The edge snake has been reported to have a fundamental toroidal mode number of 1 [14]. As can be seen this is also the case for the edge snake in figure 14.…”

Section: Perpendicular Structure Of Smpssupporting

confidence: 61%

“…In addition to ELMs, various other H-mode edge instabilities have been reported to show a characteristic signature recorded by magnetic probes. For the edge snake [14], the palm tree mode [15] and the outer mode [16] this signature diverges from a sine towards phases of constant signal, periodically interrupted by solitary excursions.…”

Section: Observation Of Smps At the Elm Onsetmentioning

confidence: 99%

“…We use a forward modelling approach, comparing measured trajectories of the time derived magnetic field with the ones resulting from basic current models. We will first apply this method to the edge snake [14], where it results in a very clear and simple answer. After that we will return to the ELM, where the situation seams to be less uniform.…”

Section: Comparison With Magnetic Fluctuations Evoked By Passing Monomentioning

confidence: 99%

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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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“…The edge snake has been reported to have a fundamental toroidal mode number of 1 [14]. As can be seen this is also the case for the edge snake in figure 14.…”

Section: Perpendicular Structure Of Smpssupporting

confidence: 61%

Section: Observation Of Smps At the Elm Onsetmentioning

confidence: 99%

Section: Comparison With Magnetic Fluctuations Evoked By Passing Monomentioning

confidence: 99%

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Solitary magnetic perturbations at the ELM onset

et al. 2012

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“…This is exactly what happens in the ELM cycle [1,158,[166][167][168][169][170][171][172][173]. Various quasi-coherent (QC) modes in H-mode plasmas appear prior to the ELM and manifest themselves as periodical oscillations with increase in time amplitude (sometimes with slowdown in frequency) up to the ELM crash [167].…”

Section: Precursors As Fast Rwmsmentioning

confidence: 67%

Plasma stability theory including the resistive wall effects

Pustovitov

2015

J. Plasma Phys.

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Plasma stabilization due to a nearby conducting wall can provide access to better performance in some scenarios in tokamaks. This was proved by experiments with an essential gain in${\it\beta}$and demonstrated as a long-lasting effect at sufficiently fast plasma rotation in the DIII-D tokamak (see, for example, Straitet al.,Nucl. Fusion, vol. 43, 2003, pp. 430–440). The rotational stabilization is the central topic of this review, though eventually the mode rotation gains significance. The analysis is based on the first-principle equations describing the energy balance with dissipation in the resistive wall. The method emphasizes derivation of the dispersion relations for the modes which are faster than the conventional resistive wall modes, but slower than the ideal magnetohydrodynamics modes. Both the standard thin wall and ideal-wall approximations are not valid in this range. Here, these are replaced by an approach incorporating the skin effect in the wall. This new element in the stability theory makes the energy sink a nonlinear function of the complex growth rate. An important consequence is that a mode rotating above a critical level can provide a damping effect sufficient for instability suppression. Estimates are given and applications are discussed.

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“…The smaller structures are no longer visible in the magnetic signal because of their weak amplitude. In Figure 4, an example of a so called edge snake [8] that has mode numbers n = −(1 . .…”

Section: Mode Number Determinationmentioning

confidence: 99%

Toroidal mode number determination of ELM associated phenomena on ASDEX Upgrade

Mink

Wolfrum

Maraschek

et al. 2016

Plasma Phys. Control. Fusion

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Abstract. In highly confined tokamak plasmas periodically appearing edge localized modes (ELMs) are accompanied by mode-like magnetohydrodynamic (MHD) activities with defined toroidal mode numbers. Here the method of determining toroidal mode numbers n on the ASDEX Upgrade tokamak with a toroidally spread magnetic pick-up coil array is reviewed and improved by taking into account intrinsic coil phases. ELM synchronization is used to characterize inter-ELM MHD activity and their development during the ELM cycle in terms of their mode numbers. The mode number development is correlated with the development of the pedestal parameters which shows that the inter-ELM modes cause transport across the pedestal. An estimation of the position of the modes is done via a comparison between the mode velocities and the plasma rotation profile at the edge. Results show that during the ELM cycle MHD modes appear at several positions in the strong gradient region with clearly defined toroidal structures in the range of n = 1 − 10. These structures of inter-ELM modes are preserved during the ELM crash where also a strong n = 0 phenomenon occurs.

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Characterization and interpretation of the Edge Snake in between type-I edge localized modes at ASDEX Upgrade

Cited by 7 publications

References 15 publications

Solitary magnetic perturbations at the ELM onset

Solitary magnetic perturbations at the ELM onset

Plasma stability theory including the resistive wall effects

Toroidal mode number determination of ELM associated phenomena on ASDEX Upgrade

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