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Magnetized plasma-wall transition layer with cold ions

Published online by Cambridge University Press:  25 January 2010

D. D. TSKHAKAYA Sr.,
F. BINT-E-MUNIR and
S. KUHN
D. D. TSKHAKAYA Sr.
Affiliation:
Association EURATOM-ÖAW, Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria (Siegbert.Kuhn@uibk.ac.at)Institute of Physics, Georgian Academy of Sciences, Tbilisi, Georgia
F. BINT-E-MUNIR
Affiliation:
Association EURATOM-ÖAW, Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria (Siegbert.Kuhn@uibk.ac.at)Department of Physics, Government College University, Lahore, Pakistan
S. KUHN
Affiliation:
Association EURATOM-ÖAW, Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria (Siegbert.Kuhn@uibk.ac.at)
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Abstract

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The magnetized plasma-wall transition (MPWT) layer occurring, for example near a tokamak diverter, typically consists of three distinct sublayers: the Debye sheath (DS), the magnetic presheath (MPS) and the collisional presheath (CPS), with characteristic lengths λD (electron Debye length), ρi (ion gyroradius) and λ (smallest relevant ion collision length), respectively. For analytical simplicity one usually assumes the ordering λD ≪ ρi ≪ λ, or, equivalently, $\varepsilon _{Dm} \equiv \frac{{\lambda _D }}{{\rho _i }} \to 0$ and $\varepsilon _{mc} \equiv \frac{{\rho _i }}{\lambda } \to 0$ (‘asymptotic three-scale (A3S) limit’), in which the three sublayers are precisely defined. In the present work the equations and length scales governing the transition, or the ‘intermediate’ regions between neighboring sublayers (DS–MPS, MPS–CPS), in the A3S limit are derived, allowing one to avoid the singularities arising from the ϵDm → 0 and ϵmc → 0 approximations. The MPS entrance and the related Bohm–Chodura condition is defined in a natural way. It is found that in the hydrodynamic Ti = 0 approximation the intermediate scales and equations have a universal form and a similar structure not only for the MPS–DS and CPS–MPS transitions but also for the DS–CPS transition in the non-magnetized case.

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