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

Medvedeva, A.; Bottereau, C.; Clairet, F.; Conway, G. D.; Mänz, P.; Mink, F.; Nikolaeva, V.; Prisiazhniuk, D.; Stroth, U.; Wolfrum, E.; Biancalani, A.; Heuraux, S.; Molina, Diego Alonso Restrepo; Silva, A; Team, EUROfusion Mst

doi:10.1088/1361-6587/ab2575

Cited by 7 publications

(7 citation statements)

References 33 publications

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“…In addition, an intermediate oscillatory phase between L-and H-mode, dubbed as 'I-phase', or as 'M-mode', has been characterized in multiple devices at a heating power close to the transition threshold. Similar observations of the AUG I-phase and the JET M-mode have been identified, in terms of the pedestal profile modulation, the high-frequency magnetic precursor oscillations and up-down symmetry [36][37][38][39]. However, an in-out asymmetry structure of the magnetic oscillations has been reported in COMPASS [40].…”

Section: Introductionsupporting

confidence: 79%

Comparison of dynamical features between the fast H-L and the H-I-L transition for EAST RF-heated plasmas

Chen¹,

Xu²,

Shao³

et al. 2022

Phys. Scr.

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In this paper, a comparison of dynamical features between the fast H-L and the H-I-L transition, which can be identified by the intermediate phase, or ‘I-phase’, has been made for radio-frequency (RF) heated deuterium plasmas in EAST. The fast H-L transition is characterized by a rapid release of stored energy during the transition transient, while the H-I-L transition exhibits a ‘soft’ H-mode termination. One important distinction between the transitions has been observed by dedicated probe measurements slightly inside the separatrix, with respect to the radial gradient of the floating potential, which corresponds to the E×B flow and/or the electron temperature gradient. The potential gradient inside the separatrix oscillates and persists during the stationary I-phase, and shows a larger amplitude than that before the fast H-L transition. The reduction of the gradient leads to the final transition to the L-mode for both the fast H-L and the H-I-L transition. These findings indicate that the mean E×B flow shear and/or edge electron temperature gradient play a critical role underlying the H-L transition physics. In addition, the back transition in EAST is found to be sensitive to magnetic configuration, where the vertical configuration, i.e., inner strike-point located at vertical target, favours access to the H-I-L transition, while the horizontal shape facilitates achievement of the fast H-L transition. The divertor recycling level normalized to electron density is higher before the fast H-L transition, as compared to that before the I-phase, which strongly suggest that the density of the recycled neutrals is an important ingredient in determining the back transition behaviour.

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Section: Introductionsupporting

confidence: 79%

Comparison of dynamical features between the fast H-L and the H-I-L transition for EAST RF-heated plasmas

Chen¹,

Xu²,

Shao³

et al. 2022

Phys. Scr.

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“…They were localized in the region between the pedestal top and the steepest pressure gradient and it was wound that their frequency scales with the pressure gradient. Moreover, LFS and HFS fixed frequency o-mode microwave RFL, indicating their presence or the presence of their effects on the inboard side of the machine [48].…”

Section: Asdex Upgradementioning

confidence: 99%

Review: Turbulence dynamics during the pedestal evolution between edge localized modes in magnetic fusion devices

Diallo

Laggner

2020

Plasma Phys. Control. Fusion

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Fusion performance has been shown to be related to the H-mode pedestal structure. The pedestal is associated with steep gradients that are the source of free energy for microinstabilities. A variety of instabilities have been shown to co-exist in the pedestal. This paper reviews the experimentally observed signatures of instabilities during the pedestal parameters’ evolutions, with a focus on turbulence observations, made in between edge localized modes (ELMs), in multiple tokamaks. ELMs are cyclic events associated with bursty relaxations of the pedestal. The multiple machine results point to very similar pedestal localized modes suggesting the existence of a unifying mechanism governing the modes’ onset and dynamics. Modeling efforts to identify the generation mechanism of these instabilities are introduced. Several remaining challenges include the study of the instability saturation mechanisms and impact on the pedestal structure formation. Potential future research avenues will require multiscale-non-linear-gyrokinetic analyses to study the non-linear interaction between these instabilities, and which pedestal conditions facilitate such non-linear interactions, as well as the relationship with the formation of the pedestal through transport.

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“…In the core region, ρ ψ ρ c = 0.8, GENE simulations give δn e,rms / n e for three values of ρ ψ and θ = π 2 , shown in figure 4(b). Therefore a constant value of 2% is chosen to match GENE results for ρ ψ ρ c , and that is connected to the interpolated GBS data by means of an analytical model guided by reflectometry measurements [42,43]. In addition, we also consider another profile, labeled 'edge only', in which δn e,rms / n e = 0 in the core so that only the edge fluctuations are accounted for.…”

Section: Wkbeam Simulations For the Mmw Beam Propagationmentioning

confidence: 99%

Millimeter-wave beam scattering and induced broadening by plasma turbulence in the TCV tokamak

Chellaï¹,

Alberti²,

Furno³

et al. 2021

Nucl. Fusion

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The scattering of millimeter-wave beams from electron density fluctuations and the associated beam broadening are experimentally demonstrated. Using a dedicated setup, instantaneous deflection and (de-)focusing of the beam due to density blobs on the beam path are shown to agree with full-wave simulations. The detected time-averaged wave power transmitted through the turbulent plasma is reproduced by the radiative-transfer model implemented in the WKBeam code, which predicts a ∼50% turbulence-induced broadening of the beam cross-section. The role of core turbulence for the considered geometry is highlighted.

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

Cited by 7 publications

References 33 publications

Comparison of dynamical features between the fast H-L and the H-I-L transition for EAST RF-heated plasmas

Comparison of dynamical features between the fast H-L and the H-I-L transition for EAST RF-heated plasmas

Review: Turbulence dynamics during the pedestal evolution between edge localized modes in magnetic fusion devices

Millimeter-wave beam scattering and induced broadening by plasma turbulence in the TCV tokamak

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