The role of turbulence–flow interactions in L- to H-mode transition dynamics: recent progress

Schmitz, L.

doi:10.1088/1741-4326/57/2/025003

Cited by 67 publications

(70 citation statements)

References 106 publications

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“…While being reproduced in different devices, the realization of the H-mode for future burning plasmas (e.g. $20 billion ITER project) remains a critical issue [5,17], with controversial issues including threshold power scaling, the effects of density, magnetic geometry and neutrals, triggering mechanisms and causality relations, hysteresis, etc. [17].…”

Section: Introductionmentioning

confidence: 99%

Time-dependent probability density functions and information geometry of the low-to-high confinement transition in fusion plasma

Kim

Hollerbach

2020

Phys. Rev. Research

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We report a first study of time-dependent Probability Density Functions (PDFs) in the Low-to-High confinement mode (L-H) transition by extending the previous prey-predator-type model (Kim & Diamond, Phys. Rev. Lett. 91, 185006, 2003) to a stochastic model. We highlight the limited utility of mean value and variance in understanding the L-H transition by showing strongly non-Gaussian PDFs, with the number of peaks changing in time. We also propose a new information geometric method by using information length, dynamical time scale, and information phase portrait, and show their utility in forecasting transitions and self-regulation between turbulence and zonal flows. In particular, we demonstrate the importance of intermittency (rare events of large amplitude) of zonal flows that can play an important role in promoting the L-H transition.

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Section: Introductionmentioning

confidence: 99%

Time-dependent probability density functions and information geometry of the low-to-high confinement transition in fusion plasma

Kim

Hollerbach

2020

Phys. Rev. Research

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“…Similar phenomena which exhibit oscillations between different phases, often called Limit Cycle Oscillations (LCOs), have been reported in various devices: COMPASS [7], DIII-D [8] [9], EAST [10][11] [12], HL-2A [13], JFT-2M [14] and TJ-II [15]. These appear close to the L-H transition and are considered as predator-prey dynamics in the flowturbulence -profile system [16] [17].…”

Section: Introductionmentioning

confidence: 99%

Identity of the JET M-mode and the ASDEX Upgrade I-phase phenomena

Réfy

Solano²,

Vianello³

et al. 2020

Nucl. Fusion

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An H-mode plasma state free of edge-localized mode (ELM), close to the L-H transition with clear density and temperature pedestal has been observed both at the Joint European Torus (JET) and at the ASDEX Upgrade (AUG) tokamaks usually identified by a low frequency (LFO, 1-2 kHz), m=1, n=0 oscillation of the magnetics and the modulation of pedestal profiles. The regime at JET is referred to as M-mode while at AUG as intermediate phase or I-phase. This contribution aims at a comparative analysis of these phenomena in terms of the density and temperature pedestal properties, the magnetic oscillations and symmetries. Lithium beam emission spectroscopy (Li-BES) and reflectometer measurements at JET and AUG show that the M-mode and the I-phase modulates the plasma edge density. A high frequency oscillation of the magnetics and the density at the pedestal is also associated with both the M-mode and the I-phase, and its power is modulated with the LFO frequency. The power modulation happens simultaneously in every Mirnov coil signal where it can be detected. The bursts of the magnetic signals and the density at the pedestal region are followed by the flattening of the density profile, and by a radially outward propagating density pulse in the scrape-off layer (SOL). The analysis of the helium line ratio spectroscopy (He-BES) signals at AUG revealed that the electron temperature is modulated in phase with the density, thus the I-phase modulates the pressure profile gradient. This analysis gave opportunity to compare Li-BES and He-BES density ‡ Identity of the JET M-mode and the ASDEX Upgrade I-phase phenomena 2 profiles at different locations suggesting a toroidal and poloidal symmetry of the density modulation. The presented results indicate that the regimes, the AUG I-phase and the JET M-mode, exhibit similar characteristics, which leads to the conclusion that the regimes are likely the same.

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“…Low frequency LCOs (~6 kHz) led to a transition to H-mode while high frequency LCOs (~8.5 kHz) resulted in the transition to L-mode or even in a disruption. The LCO frequencies in Globus-M are much higher in comparison to medium size devices [47]. A strong radial dependence of LCO frequency was not predicted by the model of limit cycle oscillations induced by a predator-prey coupling of turbulence with zonal flows [48].…”

Section: Limit Cycle Oscillationsmentioning

confidence: 82%

“…It was shown that an SMBI pulse can reduce the Doppler shift frequency, which corresponds to the flattening of the electric field. In a series of experiments on the EAST tokamak using two separate DBS systems, one for the Q-band (33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50) and the other for the V-band (50-75 GHz), Doppler shifted signals were obtained and radial profiles of perpendicular velocities were computed for the L-and H-mode [15]. In the Globus-M2 tokamak, the first results of the Doppler backscattering diagnostics during a discharge with the L-H transition show that the transition process is linked to the deformation of the poloidal rotation velocity profile [16].…”

Section: Introductionmentioning

confidence: 99%

Review of Advanced Implementation of Doppler Backscattering Method in Globus-M

et al. 2021

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Doppler backscattering (DBS) is a microwave diagnostics method typically used to study the plasma rotation velocity. Apart from conventional techniques, more advanced forms of DBS implementation were suggested on Globus-M. More specifically the study of a variety of oscillating processes was performed using DBS. In this review we present a detailed description of all of the methods and techniques employed in Globus-M alongside results obtained using DBS in all the years up until the shutdown of the tokamak. These include research similar to that done on other devices into the properties of such phenomena like geodesic acoustic modes or limit cycle oscillations, along with innovative works regarding the detection and investigation of Alfven eigenmodes and filaments that were the first of their kind and that provided important and novel results. Apart from that, the specific aspects of DBS application on a spherical tokamak are discussed. An in-depth look into the gradual change and improvement of the DBS diagnostics on Globus-M is also presented in this paper.

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The role of turbulence–flow interactions in L- to H-mode transition dynamics: recent progress

Cited by 67 publications

References 106 publications

Time-dependent probability density functions and information geometry of the low-to-high confinement transition in fusion plasma

Time-dependent probability density functions and information geometry of the low-to-high confinement transition in fusion plasma

Identity of the JET M-mode and the ASDEX Upgrade I-phase phenomena

Review of Advanced Implementation of Doppler Backscattering Method in Globus-M

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