Transport analysis of the effect of zonal flows on electron internal transport barriers in toroidal helical plasmas

Toda, S.; Itoh, K.; Fujisawa, A.; Itoh, Sanae I.; Yagi, M.; Fukuyama, A.; Diamond, P. H.; Ida, K.

doi:10.1088/0029-5515/47/8/024

Cited by 14 publications

(14 citation statements)

References 27 publications

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“…Observations of the e-ITB in Wendelstein 7-AS [2], the Large Helical Device (LHD) [3,4], and other experiments followed [5]. In a previous study of the e-ITB [6], we have shown a reduction in heat diffusivity because of the effect of zonal flows (ZFs), which qualitatively predicts the e-ITB experimentally observed in the entire region of the strong positive E r . However, in that study we excluded the radial and temporal changes in the particle diffusivity due to the effect of ZFs.…”

Section: Introductionsupporting

confidence: 71%

“…The region 0 < ρ < 1 is considered, where ρ = r/a and a is the minor radius. The temporal equations for the density (n), electron temperature (T e ) and the hydrogen ion temperature (T i ) in this article are those given in [6]. The expression for the radial neoclassical flux associated with helical-ripple trapped particles is denoted by the symbol Γ na j for species j.…”

Section: One-dimensional Model For Transport Equationsmentioning

confidence: 99%

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Theoretical Modeling of Transport Barriers in Helical Plasmas

Toda

Itoh

Ohyabu

2010

Plasma and Fusion Research

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A unified transport model is proposed to study the physical mechanism for the formation of electron internal transport barriers (e-ITB) in helical plasmas and internal diffusion barriers (IDB) observed in the Large Helical Device (LHD). An e-ITB can be predicted with the effect of zonal flows (ZFs) in the low collisional regime when the radial variation in particle turbulent diffusivity is included. The transport analysis in this article shows that particle fueling induces IDB formation when the unified transport model is used in the high collisional regime. After particle fueling, a steep density gradient forms. To examine the density limit for the IDB in helical toroidal plasmas, the effect of radiation loss is included in a set of transport equations.

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Section: Introductionsupporting

confidence: 71%

Section: One-dimensional Model For Transport Equationsmentioning

confidence: 99%

Theoretical Modeling of Transport Barriers in Helical Plasmas

Toda

Itoh

Ohyabu

2010

Plasma and Fusion Research

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“…Such bifurcation is also observed in tokamaks, and theoretical works reveal that poloidal and toroidal rotations of plasmas play key roles, screening the penetration of RMPs [5]. In helical plasmas, the poloidal rotation is driven by E × B and diamagnetic drifts, where radial electric fields are produced by the neoclassical particle diffusion associated with helically rippled magnetic fields [6]. Therefore, the poloidal rotation might be associated with the self-healing mechanism.…”

mentioning

confidence: 94%

Forced Magnetic Reconnection in Helical Plasmas

Nishimura

Narushima

Toda

et al. 2010

Plasma and Fusion Research

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Magnetic islands excited by resonant magnetic perturbations (RMPs) in helical plasmas are investigated. A Rutherford-type equation is coupled with the time evolution equation of the radial electric field associated with the neoclassical particle diffusion due to helically rippled magnetic fields. Using the model, bifurcation between the excitation and the annihilation of non-rotating magnetic islands are newly observed, depending on the magnitude of RMPs and the anomalous plasma viscosity. It is found that the transition between these states is triggered by the change in the radial electric field profile in the vicinity of magnetic island. Keywords: magnetic island, radial electric field, plasma rotation, neoclassical particle diffusion DOI: 10.1585/pfr.5.040Forced magnetic reconnection due to resonant magnetic perturbations (RMPs) is of great interest in magnetic fusion plasmas. Bifurcation of equilibria between with and without magnetic islands is observed in helical devices such as the LHD [1, 2] and the TJ-II [3], where the tearing mode is linearly stable. In particular, spontaneous annihilation of magnetic islands called 'self-healing' triggers the improvement of plasma confinements. Magnetic islands and stochastic layers in helical plasmas have been investigated in the context of the three-dimensional resistive magnetohydrodynamics (MHD) equilibrium [4], and mechanism of the self-healing is under investigation. Such bifurcation is also observed in tokamaks, and theoretical works reveal that poloidal and toroidal rotations of plasmas play key roles, screening the penetration of RMPs [5]. In helical plasmas, the poloidal rotation is driven by E × B and diamagnetic drifts, where radial electric fields are produced by the neoclassical particle diffusion associated with helically rippled magnetic fields [6]. Therefore, the poloidal rotation might be associated with the self-healing mechanism. In order to test this hypothesis, theoretical models including finite Lamor radius (FLR) effects, such as the neoclassical particle diffusion, are necessary.In this paper, we introduce a simple theoretical model describing the forced magnetic reconnection in helical plasmas, and the bifurcation mechanism associated with the poloidal rotation is examined.The derivation of the model equations is outlined below. We start from two-fluids equations including FLR effects based on the drift ordering [7]. Perpendicular electric current is composed of the polarization current, the diamagnetic current and currents due to anisotropic presauthor's e-mail: nishimura.seiya@lhd.nifs.ac.jp sure tensors. Neoclassical particle fluxes are perturbatively included by substituting gyrophase-averaged distribution functions given by linearized drift-kinetic equations into moment formulae of anisotropic pressure tensors. We adopt a simplified version of the radial neoclassical particle fluxes given in Ref. [8]. For parallel electric currents, we focus on the regime where the bootstrap current is less important than the inductive current. In fact, ...

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“…Here, T e and T i denote the electron and ion temperatures, respectively. For example, particle and heat transport improve as T i / T e is increased, as recognized in DIII-D. 3 The damping rate of the zonal flow is predicted to depend on the radial electric field ͑E r ͒ in helical plasmas, where E r is strongly affected by the temperature ratio, 4 through the ambipolarity condition based on neoclassical ͑NC͒ particle fluxes. 5 LHD plasmas typically have had a higher T e than T i due to the electron-predominant heating from the high-energy neutral beam injection ͑NBI͒ heating.…”

Section: Introductionmentioning

confidence: 91%

Extension of the high-ion-temperature regime in the Large Helical Device

Yokoyama¹,

Nagaoka²,

Yoshinuma³

et al. 2008

Physics of Plasmas

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High-ion-temperature ͑exceeding 5 keV͒ hydrogen plasmas have been successfully produced in the Large Helical Device ͓Iiyoshi et al., Nucl. Fusion 39, 1245 ͑1999͒; Motojima et al., Nucl. Fusion 47, S668 ͑2007͔͒ with the ion heat confinement improvement in the core region. The experimental ion heat diffusivity at the core region is found to be almost independent of the ion temperature, T i ͑even decreasing as T i increases͒. The neoclassical ͑NC͒ ripple transport is suppressed by the ambipolar radial electric field, E r ͑Ͻ0͒ predicted by NC transport fluxes. The temperature ratio, T i / T e , is one of the key parameters to reduce the NC ambipolar particle and heat fluxes. Thus, it is suggested that the selective ion heating ͑making T i / T e larger͒ is a plausible approach to further increase T i . Spontaneous rotation is evaluated in these high-T i plasmas, in which a co-directed component is recognized at the radial location with a large T i gradient, in addition to the tokamak-like counter-directed component expected for E r Ͻ 0.

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Transport analysis of the effect of zonal flows on electron internal transport barriers in toroidal helical plasmas

Cited by 14 publications

References 27 publications

Theoretical Modeling of Transport Barriers in Helical Plasmas

Theoretical Modeling of Transport Barriers in Helical Plasmas

Forced Magnetic Reconnection in Helical Plasmas

Extension of the high-ion-temperature regime in the Large Helical Device

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