Intrinsic plasma rotation and Reynolds stress at the plasma edge in the HSX stellarator

Wilcox, R.S.; Talmadge, J. N.; Anderson, David T.; Anderson, F. S. B.; Lore, J.

doi:10.1088/0029-5515/56/3/036002

Cited by 8 publications

(10 citation statements)

References 47 publications

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“…It is found that the local Reynolds stress and the resulting zonal flow drive are concentrated on the outboard side, where the normal curvature is negative. These measurements go beyond previously published results [16,17] and motivate complementary turbulence simulations in 3D geometry in order to quantitatively address the magnetic field dependence of microscopic (drift-wave turbulence) and macroscopic (zonal flow) dynamics. This paper is organised as follows.…”

Section: Introductionsupporting

confidence: 58%

Spatio-temporal structure of turbulent Reynolds stress zonal flow drive in 3D magnetic configuration

et al. 2017

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The poloidal dependence of the zonal flow drive and the underlying Reynolds stress structure are studied at the stellarator experimentTJ-K by means of a poloidal Langmuir-probe array. This gives the unique possibility to study the locality of the Reynolds stress in a complex toroidal magnetic geometry. It is found that the Reynolds stress is not homogeneously distributed along the flux surface but has a strong poloidal asymmetry where it is concentrated on the outboard side with a maximum above the midplane. The average tilt of the turbulent structures is thereby reflected in the anisotropy of the bivariant velocity distribution. Using a conditional averaging technique the temporal dynamics reveal that the zonal flow drive is also maximal in this particular region. The results suggest an influence of the magnetic field line curvature, which controls the underlying plasma turbulence. The findings are a basis for further comparison with turbulence simulations in 3D geometry and demonstrate the need for a global characterisation of plasma turbulence.

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Section: Introductionsupporting

confidence: 58%

Spatio-temporal structure of turbulent Reynolds stress zonal flow drive in 3D magnetic configuration

et al. 2017

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“…To point this out explicitly, it is possible to both over and underestimate the flux-surface average Reynolds stress by taking a local measurement only. The Reynolds stress have been experimentally found to have the opposite sign at two different poloidal locations [38]. From the present study it can be concluded that a better understanding of the spatial distribution of the Reynolds stress is necessary for a proper interpretation of local measurements involving simulations with realistic field geometry.…”

Section: Discussionmentioning

confidence: 53%

Magnetic configuration effects on the Reynolds stress in the plasma edge

et al. 2018

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Breaking the poloidal symmetry of the magnetic shear induced tilt of turbulent structures, by either divertor X-point resistivity or limiter positions, can lead to a finite (residual) contribution to the flux-surface averaged radial-binormal Reynolds stress. This residual stress supports or works against the radial electric field at the plasma edge of a tokamak. The impact of divertor geometry on the poloidal pattern of the Reynolds stress is studied by flux-coordinate-independent fluid simulations. Clear modifications of the Reynolds stress are found due to the magnetic shear in the confined region. The impact of different poloidal limiter positions on the radial electric field and the Reynolds stress is studied by means of magnetic field aligned gyrofluid simulations. Only if the limiter is close to the outer midplane can its position have a substantial effect on the radial electric field.

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“…Estimates indicate that if the neutral friction were lowered, turbulent Reynolds stress could also be more significant than neoclassical viscosity in QHS [8]. Previous probe measurements of Reynolds stress suggested that the Reynolds stress could drive significant flow in the edge of HSX, though the result was not conclusive because only two measurements of Reynolds stress were made on a flux surface [32].…”

Section: Discussionmentioning

confidence: 99%

The role of neutral friction in governing parallel flows in the HSX stellarator

Dobbins¹,

Kumar²,

Talmadge³

et al. 2019

Nucl. Fusion

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Experimentally measured parallel ion flows in the standard quasihelically symmetric configuration of the HSX stellarator show a large discrepancy with previous neoclassical calculations, whereas flow in a symmetry degraded configuration is in reasonably good agreement with neoclassical theory. To examine this discrepancy, the neoclassical transport code PENTA has been modified to include collisions with background neutrals. It has been found that the flow damping due to ion-neutral friction significantly modifies the ion parallel flows in the standard configuration. This makes the modeling of the ion parallel flow agree better with the experimental measurements. In the symmetry degraded configuration, higher neoclassical viscosity makes the flow damping arising from neutral friction less important. The bootstrap current was found to be insensitive to the neutral friction as the decrease in ion flow was matched by an increase in the electron flow.

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Intrinsic plasma rotation and Reynolds stress at the plasma edge in the HSX stellarator

Cited by 8 publications

References 47 publications

Spatio-temporal structure of turbulent Reynolds stress zonal flow drive in 3D magnetic configuration

Spatio-temporal structure of turbulent Reynolds stress zonal flow drive in 3D magnetic configuration

Magnetic configuration effects on the Reynolds stress in the plasma edge

The role of neutral friction in governing parallel flows in the HSX stellarator

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