The effect of the radial electric field on the L–H transitions in tokamaks

Rozhansky, V.; Тендлер, М.

doi:10.1063/1.860463

Cited by 141 publications

(165 citation statements)

References 28 publications

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“…45 Rozhansky and Tendler 46 have constructed a model that approximately predicts the radial conductivity in the L mode in TUMAN-3. This model assumes that there exists anomalous shear viscosity to damp the toroidal flow.…”

Section: ٌ͉͉͗͘mentioning

confidence: 99%

Measurements and modeling of plasma flow damping in the Helically Symmetric eXperiment

et al. 2005

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Fusion Technology 27, 273 ͑1995͔͒ using a biased electrode to impulsively spin the plasma and Mach probes to measure the rotation. There is a distinct asymmetry between the spin-up when the bias is initiated and relaxation when the electrode current is broken. In each case, two time-scales are observed in the evolution of the plasma flow. These observations motivate the development of new neoclassical modeling techniques, including a new model where the fast increment of the electric field initiates the spin-up process. The flow in the quasisymmetric configuration rises more slowly and to a higher value than in a configuration with the quasisymmetry broken, and the rise time-scale is in reasonable agreement with the neoclassical spin-up model. The flows decay more slowly in the quasisymmetry configuration than in the configuration with the quasisymmetry broken, although the decay rates are significantly faster than the neoclassical prediction.

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Section: ٌ͉͉͗͘mentioning

confidence: 99%

Measurements and modeling of plasma flow damping in the Helically Symmetric eXperiment

et al. 2005

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“…A possible explanation is that with ED the electrons move faster than massive ions along the field lines to the wall so that a positive E r must be created to restore the ambipolarity. Theory [15][16][17] predicts that the negative neoclassical ambipolar electric field will be reduced when the radial conductivity associated with the magnetic field stochasticty st becomes of the order of the neoclassical conductivity neo . The first of these is given by st O k b 2 r , where k is the Spitzer-Harm conductivity, of order 10 6 , and b r is the ratio of the perturbed to the main magnetic field.…”

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Influence of the Static Dynamic Ergodic Divertor on Edge Turbulence Properties in TEXTOR

Weynants

Jachmich

et al. 2006

Phys. Rev. Lett.

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Systematic measurements on the edge turbulence and turbulent transport have been made by Langmuir probe arrays on TEXTOR under various static Dynamic Ergodic Divertor (DED) configurations. Common features are observed. With the DED, in the ergodic zone the local turbulent flux reverses sign from radially outwards to inwards. The turbulence properties are profoundly modified by energy redistribution in frequency spectra and suppression of large scale eddies. The fluctuation poloidal phase velocity changes direction from electron to ion diamagnetic drift, consistent with the observed reversal of the E r B flow. In the laminar region, the turbulence is found to react to an observed reduced flow shear. [4] have demonstrated that an ergodized magnetic boundary can be effective to optimize the plasma-wall interaction. Meanwhile, the local effects of the magnetic ergodization on edge turbulence and turbulent cross-field transport have also been studied both experimentally [1,5,6] and theoretically [7,8]. It has been observed on TEXT [1] and Tore Supra [2,5,6] that in the ergodic divertor (ED) configuration the edge density fluctuations are decreased whereas the turbulent cross-field diffusivity is less affected. However, a systematic investigation of the turbulence properties, such as frequency and wave-number spectra and the fluctuation propagations, has not been made or was done for a reduced set of wavenumber values [5]. A distinct description in the ergodic and laminar zones was also not given.Recently, on the tokamak TEXTOR the Dynamic Ergodic Divertor (DED) [4] has been installed at the high-field side of the torus (R=a 1:75=0:47 m), contrary to other machines where the ED coils were mounted at the low-field side [1][2][3]. The DED consists of 16 perturbation coils oriented parallel to the field lines on the magnetic flux surface with a safety factor q 3. With different current distributions in the coils, the base poloidal/toroidal modes, m=n, can be adjusted as 12=4, 6=2, and 3=1. The penetration depth into the plasma depends on m: In 12=4 the influence is restricted to the plasma boundary, while in 3=1 it can reach much deeper. In the outer plasma layer, DED induces stochastization of the magnetic field lines, including an ergodic zone with long and a laminar zone with short connection lengths to the wall [9]. In this Letter, we present the first systematic measurements by Langmuir probe arrays on the edge turbulence properties and fluctuation-driven transport in the presence of various static DED configurations (dc current on the coils).To get effective impacts of the DED at the plasma boundary, the discharge conditions have been optimized as follows: For m=n 12=4, I p 250 kA, B T 1:4 T, R=a 1:73=0:46 m, dc DED current I DED 12 kA; for 6=2, I p 270 kA, B T 1:9 T, R=a 1:73=0:46 m, I DED 6 kA; and for 3=1, I p 250 kA, B T 1:9 T, R=a 1:75=0:48 m, I DED 1 kA. The I DED is applied during the stationary phase of the Ohmic discharge. In all cases, no external tearing modes are excited, the lineaveraged plasma densit...

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“…To discuss the radial electric field in tokamak, several theoretical models were proposed [3,[6][7][8][9]. The strong radial electric field emerges due to the orbit loss of particles through the separatrix [6].…”

Section: Introductionmentioning

confidence: 99%

Estimates of the Radial Electric Field in Tokamak‐Like Plasmas

2009

Contrib. Plasma Phys.

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The radial electric field is studied in tokamak-like plasmas using a simple one dimensional model. The simulation results show that in the core plasma region, the radial electric field generally follows the toroidal velocity term, whereas at the edge, the pressure gradient term is more significant. Simultaneously, the effect of the poloidal velocity term on the radial electric field is associated with the poloidal rotation velocity near the separatrix. In addition, the ambipolar radial electric field in the non-ambipolar state is also discussed in this paper.

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The effect of the radial electric field on the L–H transitions in tokamaks

Cited by 141 publications

References 28 publications

Measurements and modeling of plasma flow damping in the Helically Symmetric eXperiment

Measurements and modeling of plasma flow damping in the Helically Symmetric eXperiment

Influence of the Static Dynamic Ergodic Divertor on Edge Turbulence Properties in TEXTOR

Estimates of the Radial Electric Field in Tokamak‐Like Plasmas

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