Comparison of toroidal viscosity with neoclassical theory

Ida, K.; Nakajima, N.

doi:10.1063/1.872091

Cited by 28 publications

(22 citation statements)

References 12 publications

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“…[11][12][13][14] There is an effect of flow damping in helical plasmas even in the toroidal direction caused by non-axisymmetry in toroidal direction, which is called the "parallel viscosity" and has been experimentally confirmed in the compact helical system (CHS) for the first time. 11,15 Spontaneous flows driven by radial electric field and ion temperature gradient were also observed where the parallel viscosity is relatively large, 16,17 and they are qualitatively consistent with neoclassical prediction. Recently, a large offset toroidal flow was observed with ion internal transport barrier (ion ITB) formation in the large helical device (LHD) and correlates with ion temperature gradient.…”

Section: Introductionmentioning

confidence: 99%

3-D effects on viscosity and generation of toroidal and poloidal flows in LHD

Nagaoka¹,

Ida²,

Yoshinuma³

et al. 2013

Physics of Plasmas

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Three-dimensional effects on plasma flows have been experimentally studied in the large helical device with 3D configurations. Spontaneous toroidal flow without net driving force using the combination of perpendicular neutral beam injection (NBI) heating and balanced tangential NBI heating has been investigated with two magnetic configurations. Co-and counter-directed spontaneous flows have been observed depending on the collisionality. Toroidal flow shear changes the sign at 0:4 < r eff < 0:6 between co-and counter-flowing plasmas, where r eff is a averaged minor radius. The detailed flow structures have been also examined at the edge region with stochastic magnetic field.

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Section: Introductionmentioning

confidence: 99%

3-D effects on viscosity and generation of toroidal and poloidal flows in LHD

Nagaoka¹,

Ida²,

Yoshinuma³

et al. 2013

Physics of Plasmas

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“…It is clear that the burst rate is inversely related to the Helium concentration, however, the values of ∆v avg are lower for the 21% and 53% He concentration discharges. One possibility for this is the additional viscosity/damping to the rotation in the presence of magnetic perturbation, which can introduce higher harmonic field ripple [45]. To investigate the role of this perturbation, the amplitude of the magnetic probe signals, filtered between 25-50kHz (to obtain the component with 30kHz and associated chirping features associated with m=4,n=1), averaged over times both with bursts and without bursts are shown in Fig (10c).…”

Section: E Ion Species Dependence Of Bursts and Estimation Of Loss Cmentioning

confidence: 99%

Role of Helium–Hydrogen ratio on energetic interchange mode behaviour and its effect on ion temperature and micro-turbulence in LHD

et al. 2018

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In the Large helical device, a change of energetic particle mode is observed as He concentration is varied in ion-ITB type experiments, having constant electron density and input heating power but with a clear increase of central ion temperature in He rich discharges. This activity consists of bursty, but damped energetic interchange modes (EICs, X Du et al., Phys. Rev. Lett. 114 p.155003 (2015)), whose occurrence rate is dramatically lower in the He-rich discharges. Mechanisms are discussed for the changes in drive and damping of the modes with He concentration. These EIC bursts consist of marked changes in the radial electric field, which is derived from the phase velocity of turbulence measured with the 2D phase contrast imaging (PCI) system. Similar bursts are detected in edge fast ion diagnostics. Ion thermal transport by gyro-Bohm scaling is recognised as a contribution to the change in ion temperature, though fast ion losses by these EIC modes may also contribute to the ion temperature dependence on He concentration, most particularly controlling the height of an "edge-pedestal" in the Ti profile. The steady-state level of fast ions is shown to be larger in Helium rich discharges on the basis of a compact neutral particle analyser (CNPA), and the fast-ion component of the diamagnetic stored energy. These events also have an influence on turbulence and transport. The large velocity shear induced produced during these events transiently improves confinement and suppresses turbulence, and has a larger net effect when bursts are more frequent in Hydrogen discharges. This exactly offsets the increased gyro-Bohm related turbulence drive in Hydrogen which results in the same time-averaged turbulence level in Hydrogen as in Helium.

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“…Measurements in CHS have shown that in configurations with large toroidal viscosity, the damping of neutral beam induced toroidal flows can be described by neoclassical theory. 9 In configurations of the device where the toroidal viscosity is reduced, anomalous shear viscosity is necessary to explain the measured damping. A similar result was observed in Wendelstein-7 Advanced Stellarator ͑W7-AS͒.…”

Section: Introductionmentioning

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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Comparison of toroidal viscosity with neoclassical theory

Cited by 28 publications

References 12 publications

3-D effects on viscosity and generation of toroidal and poloidal flows in LHD

3-D effects on viscosity and generation of toroidal and poloidal flows in LHD

Role of Helium–Hydrogen ratio on energetic interchange mode behaviour and its effect on ion temperature and micro-turbulence in LHD

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

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