2D electron cyclotron emission imaging at ASDEX Upgrade (invited)

Classen, I. G. J.; Boom, J.; Suttrop, W.; Schmid, E.; Tobias, Benjamin; Domier, Calvin; Luhmann, Neville C.; Donné, A. J. H.; Jaspers, R.; Vries, P. C. de; Park, H. K.; Munsat, T.; García-Muñoz, M.; Schneider, P. A.

doi:10.1063/1.3483214

Cited by 95 publications

(82 citation statements)

References 13 publications

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“…As soon as the q = 2 surface is crossed, a strong mode activity around 60 kHz is observed. It is clearly visible in the magnetic pick-up coils, in the central soft-X-ray channels (SXR-J 51) [27], the ECEI [28] and in the fast-ion loss detector (FILD) [29,30]. In fact, the losses between t = 0.44 − 0.58s are the only losses detected in this discharge.…”

Section: Experimental Observationsmentioning

confidence: 98%

NBI-driven Alfvénic modes at ASDEX Upgrade

Lauber

Classen

Curran³

et al. 2012

Nucl. Fusion

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Abstract. A large variety of electromagnetic modes excited by NBI-generated energetic ions are observed in the early phase of many discharges at ASDEX Upgrade. In addition to the well known reversed shear Alfvén eigenmodes (RSAE) and the toroidal Alfvén eigenmodes (TAE), a set of modes around 70 kHz is observed as recently described in [7]. The modes were identified to be beta-induced Alfvén eigenmodes (BAE) connected with the appearance of the q = 2 and the q = 1.5 surface during the current ramp-up phase. In the view of ITER, these BAEs may occur in scenarios with q ≈ 2 (scenario 4) and therefore add significantly to the transport of energetic ions due to RSAEs and TAEs. Experimentally, the combination of ECE, Soft-X-ray and magnetic measurements allows for a very reliable mode position and mode structure determination. The measurements are compared with linear gyrokinetic calculations employing the LIGKA code that uses a fully kinetic model to describe fast-particle-driven modes in general tokamak geometry .

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Section: Experimental Observationsmentioning

confidence: 98%

NBI-driven Alfvénic modes at ASDEX Upgrade

Lauber

Classen

Curran³

et al. 2012

Nucl. Fusion

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“…Here, T rad,avg is the average radiation temperature taken at the end of the crash. Assuming locally increased electron densities [29] inside a filament, the optical thickness inside the structure could (marginally) be above unity [23]. So, although these measurements are obtained from regions just at and outside the separatrix, the radiation temperatures (with maxima up to 200 eV) are still assumed to be strongly correlated to the electron temperature.…”

Section: Elm Crash and Filamentsmentioning

confidence: 99%

“…The ECEI diagnostic, as it is installed at AUG consists of an array of 16 detectors, each of which acts as a standard (1D) ECE radiometer [23][24][25]. That is, every detector measures the intensity of the emitted electron cyclotron radiation from different vertical positions, here in 2 nd harmonic X-mode (100-140 GHz).…”

Section: Description Of the Diagnostic And Experimental Setupmentioning

confidence: 99%

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

et al. 2011

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The installation of a 2D electron cyclotron emission imaging (ECEI) diagnostic on ASDEX Upgrade has provided a new means to observe the nature of Edge Localized Modes (ELMs). For a series of ELMs in a typical type-I ELMy H-mode (with q 95 = 4.7), the 2D dynamics have been characterized. Firstly, a clear distinction between so-called 'fast' and 'slow' ELMs was found to be the occurrence of an off-mid-plane fluctuation in case of the latter. This mode has its amplitude strongest off-midplane and its poloidal and toroidal mode numbers are m ~ 110 and n ~ 30. Secondly, prior to the onset of the ELM's temperature collapse, a mode is observed that covers the whole ECEI observation window. Here, the estimated poloidal and toroidal mode numbers are m ~ 75 and n ~ 20. These have been seen to increase towards the ELM crash, simultaneously with a velocity increase of the mode (in poloidal direction). Finally, filaments have been identified during the temperature collapse phase and their motion could be followed in the vertical direction. Contrary to both the off-mid-plane fluctuation and the ELM onset mode, which only have been seen rotating in the electron diamagnetic drift direction, the first few filaments have sometimes been observed to move in the opposite direction as well.

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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 electron cyclotron emission imaging at ASDEX Upgrade (invited)

Cited by 95 publications

References 13 publications

NBI-driven Alfvénic modes at ASDEX Upgrade

NBI-driven Alfvénic modes at ASDEX Upgrade

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

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

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