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Flux of Parallel Flow Momentum by Parallel Shear Flow Driven Instability

Yusuke KOSUGA^1,2), Sanae-I. ITOH^2,3) and Kimitaka ITOH^3,4)

1)

Institute for Advanced Study, Kyushu University, Fukuoka 812-8581, Japan

2)

Research Institute for Applied Mechanics, Kyushu University, Fukuoka 816-8580, Japan

3)

Research Center for Plasma Turbulence, Kyushu University, Fukuoka 816-8580, Japan

4)

National Institute for Fusion Science, Toki 509-5202, Japan

(Received 18 January 2016 / Accepted 29 January 2016 / Published 17 March 2016)

Abstract

The flux of parallel momentum by parallel shear flow driven instability is calculated with the self-consistent mode dispersion. The result indicates that the diffusive component has two characteristic terms: ν_D1 ∼ v˜_x²/γ₍₀₎ and ν_D2 ∼ v˜_x²/(k_∥²D_∥) where v˜_x is the fluctuation radial velocity, γ₍₀₎ is the growth rate of the mode, k_∥ is the parallel wave number, and D_∥ is the electron diffusivity along the magnetic field. ν_D1 results when the parallel flow shear is above the threshold, while ν_D2 is important around the marginal state. Since typically ν_D1 ≫ ν_D2 ∼ D_n, where D_n is the particle diffusivity, the Prandtl number (≡ ν/D_n) becomes large when parallel flow shear driven instability occurs. This feature may explain the experimental observation on the difference between profiles of density and toroidal flow in edge and SOL plasmas.

Copyright (c) 2016 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

parallel shear flow instability, dispersion relation, flux of parallel momentum

DOI: 10.1585/pfr.11.1203018

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