2D ECE measurements of type-I edge localized modes at ASDEX Upgrade

Boom, J.; Classen, I. G. J.; Vries, P. C. de; Eich, T.; Wolfrum, E.; Suttrop, W.; Wenninger, R.; Donné, A. J. H.; Tobias, B.; Domier, Calvin; Luhmann, N. C.; Park, H.K.

doi:10.1088/0029-5515/51/10/103039

Cited by 42 publications

(67 citation statements)

References 34 publications

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“…The Edge Snake is also visible in the 2D electron temperature measured by the 2D ECE [11], which covers a 11 × 30 cm cross section of the plasma around the separatrix on the low field side. In the first row of Figure 5 the movement of the Edge Snake for consecutive time frames can be seen, while the first plot shows the unperturbed case.…”

Section: Occurrence In the 2d Electron Temperature Measurementmentioning

confidence: 88%

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

Sommer

Günter

Kallenbach

et al. 2011

Plasma Phys. Control. Fusion

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Abstract.A new magneto-hydro-dynamic instability called 'Edge Snake', which was found in 2006 at the Tokamak ASDEX Upgrade during type-I ELMy H-modes, is investigated. It is located within the separatrix in the region of high temperature and density gradients and has a toroidal mode number of n = 1. The Edge Snake consists of a radially and poloidally strongly localized current wire, in which the temperature and density profiles flatten. This significant reduction of pressure gradient leads to a reduction of the neoclassical Bootstrap current and can plausibly explain the drive of the instability. The experimental observations point towards a magnetic island with a defect current inside the O-point of the island. The Edge Snake is compared to similar instabilities at JET, DIII-D and ASDEX Upgrade.

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Section: Occurrence In the 2d Electron Temperature Measurementmentioning

confidence: 88%

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

Sommer

Günter

Kallenbach

et al. 2011

Plasma Phys. Control. Fusion

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“…In [5] a coherent mode with around 18 peaks per toroidal turn appearing a few hundred µs before t I,div,ons has been reported. It is important to note that for the ELM shown in figure 15 such a mode has not been observed.…”

Section: Temperature Perturbation Associated With Smpsmentioning

confidence: 93%

“…The positions of the probes of two poloidal and one toroidal array can be seen in figure 3. Other fast sampling diagnostic systems which we have employed are the electron cyclotron emission imaging (ECEI) system [5], fast framing cameras and the measurement of the divertor current. These will be briefly described in the relevant sections.…”

Section: Introductionmentioning

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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“…Type-II ELMs [10,11] are characterized by a continuous broadband edge fluctuation [12]. Recently, measurements using the electron cyclotron emission imaging (ECEI) diagnostic [13] on ASDEX Upgrade revealed the 2D dynamics of edge electron temperature fluctuations in both type-I [14] and type-II [15] ELMs. This paper gives an overview of the properties and dynamics of the various edge temperature fluctuations observed on ASDEX Upgrade.…”

Section: Introductionmentioning

confidence: 99%

The role of temperature fluctuations in the dynamics of type-I and type-II edge localized modes at ASDEX Upgrade

Classen

Boom²,

Bogomolov³

et al. 2013

Nucl. Fusion

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Abstract. 2D temperature measurements using the electron cyclotron emission imaging diagnostic at ASDEX Upgrade revealed a variety of temperature fluctuations associated with type-I and type-II edge localized modes (ELMs). The characteristics and dynamics of these modes, and their role in the ELM cycle, are presented. During type-I ELMs, different phases of distinct mode activity have been identified. At the onset of the ELM crash, a short lived mode is observed in the pedestal region. During the actual crash phase, multiple filamentary structures are observed just outside the separatrix. A third type of fluctuation, the inter-ELM mode, is often observed in between type-I crashes. The occurrence of this mode tends to lengthen the ELM period. During type-I ELM suppression with magnetic perturbation coils, smaller crash events become more frequent, replacing the large type-I crashes. In type-II ELMs, temperature crashes are absent altogether, and a continuous broadband fluctuation in the 20-60kHz range, showing beat-wave like behaviour, is observed. The similarities between the characteristics of this mode and the inter-ELM mode suggest that it is the same instability. In type-I ELMs it delays the next crash, in type-II ELMs it might be responsible for the complete absence of crash events.

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2D ECE measurements of type-I edge localized modes at ASDEX Upgrade

Cited by 42 publications

References 34 publications

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

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

Solitary magnetic perturbations at the ELM onset

The role of temperature fluctuations in the dynamics of type-I and type-II edge localized modes at ASDEX Upgrade

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