Effect of the radial electric field on the fluctuation-produced transport in the H-1 heliac

Shats, Michael

doi:10.1088/0741-3335/41/11/303

Cited by 32 publications

(51 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…They reflect reports from experiments that a transition to a quiescent H-mode can be achieved followed by the onset of oscillatory behaviour, or edge-localised modes (ELMs), as the power input continues to be increased [24,25,26,27]. The original Sugama-Horton model was found to exhibit a chaotic time series for a particular set of parameter values in Ball, Dewar, Sugama: Metamorphosis of plasma turbulence-shear flow dynamics .…”

Section: IVsupporting

confidence: 66%

Metamorphosis of plasma turbulence–shear-flow dynamics through a transcritical bifurcation

2002

View full text Add to dashboard Cite

The structural properties of an economical model for a confined plasma turbulence governor are investigated through bifurcation and stability analyses. A close relationship is demonstrated between the underlying bifurcation framework of the model and typical behavior associated with low-to high-confinement transitions such as shear flow stabilization of turbulence and oscillatory collective action. In particular, the analysis evinces two types of discontinuous transition that are qualitatively distinct. One involves classical hysteresis, governed by viscous dissipation. The other is intrinsically oscillatory and non-hysteretic, and thus provides a model for the so-called dithering transitions that are frequently observed. This metamorphosis, or transformation, of the system dynamics is an important late side-effect of symmetry-breaking, which manifests as an unusual non-symmetric transcritical bifurcation induced by a significant shear flow drive. Typeset by REVT E X 1Ball, Dewar, Sugama: Metamorphosis of plasma turbulence-shear flow dynamics . . . I.Fusion plasmas, and possibly other quasi two-dimensional fluid systems, may undergo a more-or-less dramatic transition from a low to a high confinement state (the L-H transition) as the power input is increased, with the desirable outcome that particle and energy confinement is greatly improved due to localized transport reduction [1]. In this work we report on a bifurcation and stability probe of an economical model for L-H transition dynamics that uncovers a mechanism by which a radical change, or metamorphosis, may occur in the qualitative nature of the dynamics. We apply the results of this analysis to clarify the relationship between the structure of the model and the physics of the process that it describes, and draw comparisons with characteristics of L-H transitions observed in various experiments.Since 1988 there has been much progress in developing low-dimensional (low-order or reduced) descriptions of L-H transition dynamics and associated oscillatory phenomena (see, for example, Refs 2,3,4,5,6,7,8,9,10,11,12,13,14,15), the driving force being the potential power of a unified, low-dimensional model as a predictive tool for the design and control of confinement states. For example, a model that speaks of the shape and extent of hysteresis in the L-H transition would help engineers who are interested in controlling access to H-mode. Given the many variables and parameters that could be varied around a hysteretic régime, it would be cheaper-i.e., save hundreds of cpu hours and/ or many expensive diagnostics-to know in advance which ones actually do affect the hysteresis, and which do not.To help construe the context in which low-dimensional descriptions of plasma dynamics are sought, it is appropriate at this stage to make some general remarks. It makes sense to try to find the simplest description of an evolving system that is consistent with the time and space scales on which one is interested in making experimental observations of that system. One...

show abstract

Section: IVsupporting

confidence: 66%

Metamorphosis of plasma turbulence–shear-flow dynamics through a transcritical bifurcation

2002

View full text Add to dashboard Cite

show abstract

“…0 region simultaneously with the G fl reversal (Fig. 3) has also been confirmed in a single shot measurement using three radially separated probes [16].…”

supporting

confidence: 60%

“…Several combinations of the triple probes described in [14,15] are used for the plasma parameter characterization. The effect of the sheared electric field on the fluctuation-produced transport is studied during the rf power step discharges described in [14,16]. The rf power is increased during the discharge in four steps from ϳ40 to ϳ90 kW as shown in Fig.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Inward Turbulent Transport Produced by Positively Sheared Radial Electric Field in Stellarators

et al. 2000

View full text Add to dashboard Cite

Inward turbulent particle transport observed in the rf heated plasma of the H-1 toroidal heliac is reproduced in the CHS heliotron/torsatron by generating a region of positive radial electric field shear (E'(r)>0) using electron cyclotron resonance heating of the plasma edge. Empirical condition of the radial reversal of the turbulent flux derived from two experiments indicates that the shear electric field might be universally responsible for the recorrelation of the density and plasma potential fluctuations leading to the inward transport.

show abstract

“…Overall, it was somewhat below but comparable to the linear growth rate [4], qualitatively consistent with considerable reduction [5], not total suppression of turbulence observed in simulations. It is worth noting that a similar behavior has been observed experimentally just prior to H-mode transition [6]. Our gyrokinetic simulations show significant broadening of k r spectrum due to zonal flows as indicated in Figure 1: k r spectrum of ambient turbulence from gyrokinetic simulation is broadened due to random shearing of eddies by self-generated E × B flows.…”

Section: Physics Of Random Shearing By Zonal Flowssupporting

confidence: 80%

Theory, simulation, and experimental studies of zonal flows

Hahm¹,

Burrell²,

Lin³

et al. 2000

View full text Add to dashboard Cite

Effect of the radial electric field on the fluctuation-produced transport in the H-1 heliac

Cited by 32 publications

References 33 publications

Metamorphosis of plasma turbulence–shear-flow dynamics through a transcritical bifurcation

Metamorphosis of plasma turbulence–shear-flow dynamics through a transcritical bifurcation

Inward Turbulent Transport Produced by Positively Sheared Radial Electric Field in Stellarators

Theory, simulation, and experimental studies of zonal flows

Contact Info

Product

Resources

About