Toroidal mode number determination of ELM associated phenomena on ASDEX Upgrade

Mink, F.; Wolfrum, E.; Maraschek, M.; Zohm, H.; Horváth, L.; Laggner, F. M.; Mänz, P.; Viezzer, E.; Stroth, U.

doi:10.1088/0741-3335/58/12/125013

Cited by 33 publications

(48 citation statements)

References 25 publications

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“…As already shown, the location of the low-frequency mode is in the upper part of the gradient region towards the pedestal top in contrast to the high-frequency modes whose position is shown to correspond to the minimum of the E r [7]. The mid-frequency modes are located even further outside -very close to the separatrix [17]. The pedestal top and the steepest gradient are separated by about 5 mm; the different modes, therefore, are spatially very close to each other.…”

Section: Interaction Between Inter-elm Modesmentioning

confidence: 65%

“…At ASDEX Upgrade, simultaneous observations of high-frequency and low-frequency inter-ELM modes, related to type I ELMs, have been reported [16]. High (200-300 kHz ) and mid-frequency (50-100 kHz ) inter-ELM modes at ASDEX Upgrade have been characterized, and have been inferred from measurements of the toroidal and poloidal mode numbers to be resonant at q-surfaces near the minimum radial electric field (E r ) field and at the separatrix, respectively [7,17]. Both frequency branches were measured with magnetic pick-up coils.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade

et al. 2018

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The steep edge gradient region of tokamak plasmas in the high confinement regime is known to drive instabilities, which cause transport. Several diagnostics are used to allow for a high degree of characterization of low-frequency modes appearing in between type-I Edge Localizes Modes (ELMs). These modes are dominantly observed in Electron Cyclotron Emission (ECE) and ECE Imaging measurements as the modulation of radiation temperature (δT rad). In the radial magnetic field (Ḃ r) measurements, the frequency range of 4 kHz to 12 kHz is observed. The position of the mode is determined to be at the upper part of the steep gradient region, the poloidal mode velocity is changing from 1.5 ± 0.5 km/s to 2.5 ± 0.5 km/s and the toroidal mode number is 13 to 14. A comparison with the measured E × B velocity leads to the conclusion that the phase velocity of the mode is smaller than 3 km/s or zero. The poloidal structure of the modes is found to be in agreement with the poloidal structure size associated with n = 13 as estimated from the equilibrium calculations. The modes are compared between two different heating phases during one discharge, and are found to differ in duration, velocity, frequency and toroidal mode number. The possibility of non-linear interaction between these modes and other, high frequency modes existing in the narrow pedestal, is assessed via bicoherence. The presented analysis gives an unprecedented picture of the mode, its position, its structure and its velocity, calling for comparison with non-linear modelling.

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Section: Interaction Between Inter-elm Modesmentioning

confidence: 65%

Section: Introductionmentioning

confidence: 99%

Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade

et al. 2018

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“…Refined evaluation methods for the magnetic measurements at ASDEX Upgrade allows the extraction of the toroidal spectrum during an ELM cycle, revealing dominant n = 2…5 components for the present discharge, corresponding to a clear shift from the linear stability analysis in which n = 5, 6 are dominating . In the simulation, n = 4 is dominating during the ELM crash ( t − t ELM = 0…2 ms), n = 1…6 have significant amplitudes, and n ≥ 7 are lower by at least a factor two in average energies.…”

Section: Type‐i Elmsmentioning

confidence: 99%

Insights into type‐I edge localized modes and edge localized mode control from JOREK non‐linear magneto‐hydrodynamic simulations

Hoelzl

Huijsmans

Orain

et al. 2018

Contributions to Plasma Physics

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Edge localized modes (ELMs) are repetitive instabilities driven by the large pressure gradients and current densities in the edge of H‐mode plasmas. Type‐I ELMs lead to a fast collapse of the H‐mode pedestal within several hundred microseconds to a few milliseconds. Localized transient heat fluxes to divertor targets are expected to exceed tolerable limits for ITER, requiring advanced insights into ELM physics and applicable mitigation methods. This paper describes how non‐linear magneto‐hydrodynamic (MHD) simulations can contribute to this effort. The JOREK code is introduced, which allows the study of large‐scale plasma instabilities in tokamak X‐point plasmas covering the main plasma, the scrape‐off layer, and the divertor region with its finite element grid. We review key physics relevant for type‐I ELMs and show to what extent JOREK simulations agree with experiments and help reveal the underlying mechanisms. Simulations and experimental findings are compared in many respects for type‐I ELMs in ASDEX Upgrade. The role of plasma flows and non‐linear mode coupling for the spatial and temporal structure of ELMs is emphasized, and the loss mechanisms are discussed. An overview of recent ELM‐related research using JOREK is given, including ELM crashes, ELM‐free regimes, ELM pacing by pellets and magnetic kicks, and mitigation or suppression by resonant magnetic perturbation coils (RMPs). Simulations of ELMs and ELM control methods agree in many respects with experimental observations from various tokamak experiments. On this basis, predictive simulations become more and more feasible. A brief outlook is given, showing the main priorities for further research in the field of ELM physics and further developments necessary.

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“…This feature necessitates to question more accurately their nature. ECMs were previously investigated in AUG in between ELMs, although they were not yet decisively identified [6,5]. In the pedestal region during the I-phase the density fluctuation amplitude decreases and the spectra become narrower compared to typical L-mode spectra ( Fig.…”

Section: Observation Of Modes With the Ufsrmentioning

confidence: 99%

High frequency edge coherent modes studied with the ultra-fast swept reflectometer on ASDEX Upgrade

Medvedeva

Bottereau

Clairet

et al. 2019

Plasma Phys. Control. Fusion

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The results on high frequency coherent modes developing at the plasma edge after L-H transitions are presented. These edge coherent modes (ECMs) observed in the I-phase, during ELM-free and ELMy H-mode phases have common characteristics, such as their frequency of 50-200 kHz, radial position and scaling of the frequency with the pressure gradient. The ultra-fast swept reflectometer with the sweep time of 1 µs has provided measurements of the mode dynamics and localisation. The ECMs propagate in the electron diamagnetic direction in the laboratory frame and are localized in the region between the pedestal top and the steepest pressure gradient.

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Toroidal mode number determination of ELM associated phenomena on ASDEX Upgrade

Cited by 33 publications

References 25 publications

Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade

Characterization of low-frequency inter-ELM modes of H-mode discharges at ASDEX Upgrade

Insights into type‐I edge localized modes and edge localized mode control from JOREK non‐linear magneto‐hydrodynamic simulations

High frequency edge coherent modes studied with the ultra-fast swept reflectometer on ASDEX Upgrade

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