Interaction between mean and fluctuating<i>E</i>×<i>B</i>shear flows on the ISTTOK edge plasma

Silva, Carlos; Duarte, P.; Fernandes, H.; Figueiredo, H.

doi:10.1088/0741-3335/54/8/085013

Cited by 13 publications

(17 citation statements)

References 27 publications

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“…Together with that, A GAM like low-frequency mode (LFM, ~12 kHz) characterized as high-coherence and near-zero cross-phase in poloidal direction is existed under positive and 0V bias while absent under negative bias at plasma-edge (∆r = -2 cm), and the spectral power of the LFM under positive bias is lower than the case of 0V bias ( figure 11). These observations may be consistent with the results in ISTTOK [23].…”

Section: Intermittent Events and Related Transportsupporting

confidence: 93%

“…The level of long-distance correlation (LDC) structures in potential fluctuation, which behaves in the similar way as the zonal flows, was observed to be amplified under positive bias on tokamaks [22][23][24] and stellarators [14,15]. Further studies showed that the LDC strength is sensitive to the polarity of bias [23] as well as magnetic perturbation, and reduces at high-density level [25].…”

Section: Introductionmentioning

confidence: 99%

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The influence of electrode biasing on plasma confinement in the J-TEXT tokamak

Sun

Chen

Zhu

et al. 2013

Plasma Phys. Control. Fusion

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The influence of both positive and negative bias on global and plasma-edge parameters has been comparatively studied with a newly designed electrode biasing system in J-TEXT tokamak. Comparing to the 0V bias case, the global particle confinement of plasma is enhanced under bias with both polarities, with the increments of central line-averaged density and soft-X ray emission as well as the reduction of edge H α radiation level. The suppression of plasma-edge fluctuations and turbulent particle transport are obviously observed under bias, in different degrees with different polarities. The potential fluctuation amplitude is observed to be increased at the vicinity of limiter under positive bias, with the existence of a peaked low frequency mode (LFM) characterized as high coherence and near-zero cross-phase poloidally in the edge region, which is not found in the negative bias case. The poloidal correlation length of turbulence is greatly enhanced under bias with both polarities, and shows a positive correlation with the amplitude of poloidal phase velocity, which is mainly driven by the local J r × B torque at plasma edge under bias. The characteristic parameters of intermittent events (i.e. blobs), including amplitude, radial velocity, related particle flux and radial size, are decreased dramatically under bias in the edge region.

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Section: Intermittent Events and Related Transportsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

The influence of electrode biasing on plasma confinement in the J-TEXT tokamak

Sun

Chen

Zhu

et al. 2013

Plasma Phys. Control. Fusion

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“…In a related vein, the GAM magnitude, like the mean v E×B , is not constant on a flux surface. Variations of some 20% or more have been reported on TEXTOR, with the GAM being larger at the mid-plane compared to the top in ISTTOK [363]. These asymmetries are discussed further in section 8.2.…”

Section: Gam Amplitudementioning

confidence: 89%

“…From the radial gradient of the GAM (rms) velocity perturbation one can estimate an equivalent shearing rate ω E×B = ∂v θ /∂r, or indirectly from the GAM width or its radial wavenumber, γ E×B = k r v 2 GAM . Estimates have been made from several devices [141,277,282,306,337,347,357,363] and generally find ω E×B rates of the order of 10 5 s −1 comparable, within a factor of 2-3, to the turbulence decorrelation rate 1/τ d . Even when applying a frequency dependent downward correction to account for the oscillatory GAM being less effective than a static velocity shear (see section 15.1) the effective shearing rate is still significant [337].…”

Section: Gam Amplitudementioning

confidence: 92%

Geodesic acoustic modes in magnetic confinement devices

Smolyakov

Ido

2021

Nucl. Fusion

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Geodesic acoustic modes (GAMs) are ubiquitous oscillatory flow phenomena observed in toroidal magnetic confinement fusion plasmas, such as tokamaks and stellarators. They are recognized as the non-stationary branch of the turbulence driven zonal flows which play a critical regulatory role in cross-field turbulent transport. GAMs are supported by the plasma compressibility due to magnetic geodesic curvature—an intrinsic feature of any toroidal confinement device. GAMs impact the plasma confinement via velocity shearing of turbulent eddies, modulation of transport, and by providing additional routes for energy dissipation. GAMs can also be driven by energetic particles (so-called EGAMs) or even pumped by a variety of other mechanisms, both internal and external to the plasma, opening-up possibilities for plasma diagnosis and turbulence control. In recent years there have been major advances in all areas of GAM research: measurements, theory, and numerical simulations. This review assesses the status of these developments and the progress made towards a unified understanding of the GAM behaviour and its role in plasma confinement. The review begins with tutorial-like reviews of the basic concepts and theory, followed by a series of topic orientated sections covering different aspects of the GAM. The approach adopted here is to present and contrast experimental observations alongside the predictions from theory and numerical simulations. The review concludes with a comprehensive summary of the field, highlighting outstanding issues and prospects for future developments.

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“…Some papers have revealed the bifurcation of an electric field [19] in the edge region that helps L-mode to H-mode transition [30]. As bias introduces a significant increase in the mean electric field shear flows, therefore, it reduces turbulence and consequently suppresses the geodesic acoustic modes [44]. Dual electrode experiment carried out on KT5C device shows that the position of the electrode in the inner region is more effective than the outer one [13,45].…”

Section: Introductionmentioning

confidence: 99%

Edge biasing and its impact on the edge and SOL turbulence

Shankar¹,

Bisai²,

Raj³

et al. 2022

Nucl. Fusion

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A theoretical study is made of the effect of edge biasing on the dynamics of the interchange turbulence in the edge and scrape-off layer (SOL) regions. A linear analysis of a set of model fluid equations shows that biasing stabilizes the small ky modes. The model equations are next solved numerically, using the BOUT++ framework, to explore the nonlinear dynamics in the presence of positive or negative bias and compared to results in the absence of bias. Positive biasing is found to lead to a larger increment in plasma density and temperature as compared to negative biasing. It is further observed that cross-correlation between density and poloidal electric field at different radial positions decreases for positive biasing and in the case of negative biasing it is almost similar to that of no biasing. Plasma density and poloidal electric field fluctuations have been investigated which show that the density fluctuations increase (decrease) for positive (negative) biasing but the radially outward flux for these biasing cases always decreases mainly due to the decrease of cross-correlation between density and poloidal electric field fluctuations.

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Interaction between mean and fluctuatingE×Bshear flows on the ISTTOK edge plasma

Cited by 13 publications

References 27 publications

The influence of electrode biasing on plasma confinement in the J-TEXT tokamak

The influence of electrode biasing on plasma confinement in the J-TEXT tokamak

Geodesic acoustic modes in magnetic confinement devices

Edge biasing and its impact on the edge and SOL turbulence

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