Turbulent transport reduction induced by transition on radial electric field shear and curvature through amplitude and cross-phase in torus plasma

Kobayashi, Tatsuya; Itoh, K.; Ido, T.; Kamiya, K.; Itoh, Sanae–I.; Miura, Y.; Nagashima, Yoshihiko; Fujisawa, A.; Inagaki, S.; Ida, K.

doi:10.1038/s41598-017-14821-y

Cited by 23 publications

(14 citation statements)

References 35 publications

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“…Reduction in the turbulent transport has been also reported, e.g. at the curvature region of the Er-well structure in H-mode [40]. In these experiments, the density turbulence is substantially suppressed at both the inner and outer Er shear regions while the variation is only moderate in the curvature region.…”

Section: H-mode Transitionmentioning

confidence: 61%

H-mode transition in the TJ-II stellarator plasmas

Estrada¹,

Hidalgo²

2023

Phil. Trans. R. Soc. A.

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Since the first H-mode transitions were observed in TJ-II plasmas in 2008, an extensive experimental effort has been done aiming at better physics understanding of confinement transitions. In this article, an overview of the main findings related to the L-H transition in TJ-II is presented including how the radial electric field is driven, what are the possible mechanisms for turbulence suppression and what are the related temporal and spatial scales that can impact the transition. The trigger of the L-H transition in TJ-II plasmas is found to be more correlated with the development of fluctuating E × B flows than with steady-state E r effects, pointing to the role played by zonal flows in mediating the transition. Experimental evidence supporting the predator–prey relationship between turbulence and flows as the basis for the L-H transition, found for the first time in TJ-II, reinforces this conclusion. Besides, the reduction in the turbulent transport at the transition is detected at the barrier region but also in a wider radial range with weak or even zero E × B flow shear, which points to other mechanisms beyond the turbulence suppression by local sheared flows. This article is part of a discussion meeting issue ‘H-mode transition and pedestal studies in fusion plasmas’.

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Section: H-mode Transitionmentioning

confidence: 61%

H-mode transition in the TJ-II stellarator plasmas

Estrada¹,

Hidalgo²

2023

Phil. Trans. R. Soc. A.

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“…Generally, bigger barrier height and width are better for confinement. Edge transport barriers appear as a result of the suppression of edge turbulence by enhanced E × B shear due to bifurcation of radial electric field at higher input power [35][36][37]. H mode pedestal height and width are usually controlled by the input heat, particle and momentum fluxes.…”

Section: Please Cite This Article As Doi: 101063/15117835mentioning

confidence: 99%

When does turbulence spreading matter?

Singh

Diamond

2020

Physics of Plasmas

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Few, if any, of the many papers on turbulence spreading, address the key question of how turbulence spreading actually affect profile structure? Here we are using a reduced model to answer that question. Turbulence spreading is most relevant near regions where the profiles support a strong intensity gradient ∇I. One such case is at the edge of an L mode discharge, near a source of turbulence (i.e., either a localized source of edge turbulence or an influx of turbulence from the Scrape off Layer (SOL)). Another is in 'No Man's Land' (NML), which connects the pedestal to the stiff core in H mode. In the case of L mode, without an edge intensity source, the turbulence intensity profile is nearly flat and spreading has a weak effect. An edge localized source increases the edge ∇I, which then drives inward spreading.Invasion of turbulence from SOL to edge softens the edge pressure gradient. In H mode, the strong shear suppression of pedestal turbulence necessarily forces a sharp ∇I in NML. This sharp ∇I drives a significant flux of turbulence from the core to the pedestal, where it is ultimately dissipated by shearing. Counter-intuitively, results indicate that spreading actually increases pedestal height and width and hence the energy content in H mode. This suggests that models of pedestal structure should include NML turbulence spreading effects. The relation of avalanches to spreading is studied. Spreading weakly affects the avalanche distribution, but the spatiotemporal correlation of intensity increases with spreading.

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“…Kim to drive up the fluctuation level in the drift-wave turbulence. The importance of the cross-phase has been noted by Kobayashi et al (2017) and experiments have measured the cross-phase and have drawn comparisons with the numerical simulations in the tokamak geometry (Tynan, Fujisawa & McKee 2009;White et al 2010;Shchepetov, Kholnov & Vasil'kov 2013;Freethy et al 2018;Guttenfelder et al 2019). Roles of the cross-phases have been studied in simple models where sheared flows are present (Naulin & Spatschek 1997;Carmargo, Tippett & Caldas 1998;Terry 2000;Terry, Newman & Ware 2001;Figarella et al 2003;Schaffner et al 2012;Birkenmeier et al 2013).…”

Section: Introductionmentioning

confidence: 95%

Suppression of turbulence in the drift-resistive plasma where zonal flow changes direction

Kim

2020

J. Plasma Phys.

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The edge region of quasi-adiabatic plasma is pedagogically simulated by the dynamics between the electric potential $\unicode[STIX]{x1D711}$ and the electron density $n$ whose equilibrium density gradient is negative and held fixed. The zonal flow (ZF) $V$ is either enforced sinusoidally or generated self-consistently from the turbulence. Cross-phase $\unicode[STIX]{x1D6FF}$ between $\unicode[STIX]{x1D711}$ and $n$ , which is important in the determination of the turbulence level and the transport, is strongly influenced by the ZF. In the region near $V=0$ , $\unicode[STIX]{x1D6FF}$ becomes negative due to the large gradient of the ZF. It is found that the instabilities are quenched there, and the fluctuations decay. The ZF thus works as a transport barrier in the region where the ZF changes direction with large gradient.

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Turbulent transport reduction induced by transition on radial electric field shear and curvature through amplitude and cross-phase in torus plasma

Cited by 23 publications

References 35 publications

H-mode transition in the TJ-II stellarator plasmas

H-mode transition in the TJ-II stellarator plasmas

When does turbulence spreading matter?

Suppression of turbulence in the drift-resistive plasma where zonal flow changes direction

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