Plasma and Fusion Research

Volume 11, 1203018 (2016)

Rapid Communications

Flux of Parallel Flow Momentum by Parallel Shear Flow Driven Instability
Yusuke KOSUGA1,2), Sanae-I. ITOH2,3) and Kimitaka ITOH3,4)
Institute for Advanced Study, Kyushu University, Fukuoka 812-8581, Japan
Research Institute for Applied Mechanics, Kyushu University, Fukuoka 816-8580, Japan
Research Center for Plasma Turbulence, Kyushu University, Fukuoka 816-8580, Japan
National Institute for Fusion Science, Toki 509-5202, Japan
(Received 18 January 2016 / Accepted 29 January 2016 / Published 17 March 2016)


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: νD1 ∼ v˜x2(0) and νD2 ∼ v˜x2/(k2D) 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. νD1 results when the parallel flow shear is above the threshold, while νD2 is important around the marginal state. Since typically νD1 ≫ νD2 ∼ Dn, where Dn is the particle diffusivity, the Prandtl number (≡ ν/Dn) 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.


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

DOI: 10.1585/pfr.11.1203018


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