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Finite Beta Electro‐Magnetic Effects at the Edge and the Role of the Scrape‐off Layer in the L‐H Transition
Author(s) -
Chankin A. V.,
Matthews G. F.
Publication year - 1998
Publication title -
contributions to plasma physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.531
H-Index - 47
eISSN - 1521-3986
pISSN - 0863-1042
DOI - 10.1002/ctpp.2150380126
Subject(s) - physics , plasma , gyroradius , radius , beta (programming language) , atomic physics , turbulence , coulomb , ion , omega , condensed matter physics , quantum mechanics , electron , thermodynamics , computer security , computer science , programming language
Abstract Magnetic induction becomes important when the skin‐depth equals the wavelength of the electrostatic drift turbulence: \documentclass{article}\pagestyle{empty}\begin{document}$ C/\sqrt 4 \pi \sigma \omega = K_ \bot ^{ - 1} $ \end{document} . It is predicted that this suppresses the longwave perturbations responsible for the bulk of the turbulent transport, providing an explanation for the L‐H transition. Since k ⟂ ρ s ≪ 1 at the edge (ρ s ‐ ion Larmor radius), this may occur at rather low β, typical of the separatrix parameters. The above equality is used to derive thresholds for the L‐H transition: β ≈ ( k ⟂ ρ s ) 2 (m e /m i )in the collisionless skin‐depth limit of very low density plasmas and \documentclass{article}\pagestyle{empty}\begin{document}$ T^3 _e \sim B^2 L_ \bot Z_{eff} /\sqrt m $\end{document} ( L ⟂‐perpendicular decay length) in the collisional skin‐depth limit of medium to high density plasmas. The latter is in a broad agreement with experiment, pointing to a possible role of low temperature collisional plasma (which is in the SOL) in the physics of the L‐H transition.