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Radio-frequency sheath excitation at the extremities of scrape-off layer plasma filaments, mediated by resonant high harmonic fast wave scattering

Published online by Cambridge University Press:  16 December 2022

Laurent Colas Open the ORCID record for Laurent Colas [Opens in a new window] ,
W. Tierens Open the ORCID record for W. Tierens [Opens in a new window] ,
J.R. Myra Open the ORCID record for J.R. Myra [Opens in a new window]  and
R. Bilato Open the ORCID record for R. Bilato [Opens in a new window]
Laurent Colas*
Affiliation:
CEA, IRFM, F-13108 Saint Paul-Lez-Durance, France
W. Tierens
Affiliation:
Max-Planck-Institut für Plasmaphysik, Boltzmannstrasse 2, D-85748 Garching, Germany
J.R. Myra
Affiliation:
Lodestar Research Corporation, 5055 Chaparral Ct., Boulder, CO 80301, USA
R. Bilato
Affiliation:
Max-Planck-Institut für Plasmaphysik, Boltzmannstrasse 2, D-85748 Garching, Germany
*
† Email address for correspondence: laurent.colas@cea.fr
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Abstract

Resonant filament-assisted mode conversion (FAMC) scattering of high harmonic fast waves (HHFW) by cylindrical field-aligned density inhomogeneities can efficiently redirect a fraction of the launched HHFW power flux into the parallel direction. Within a simplified analytic approach, this contribution compares the parallel propagation, reflection and dissipation of nearly resonant FAMC modes for three magnetic field line geometries in the scrape-off layer, in the presence of radio-frequency (RF) sheaths at field line extremities and phenomenological wave damping in the plasma volume. When a FAMC mode, excited at the HHFW antenna parallel location and guided along the open magnetic field lines, impinges onto a boundary at normal incidence, we show that it can excite sheath RF oscillations, even toroidally far away from the HHFW launcher. The RF sheaths then dissipate part of the power flux carried by the incident mode, while another part reflects into the FAMC mode with the opposite wave vector parallel to the magnetic field. The reflected FAMC mode in turn propagates and can possibly interact with the sheath at the opposite field line boundary. The two counter-propagating modes then form in the bounded magnetic flux tube a lossy cavity excited by the HHFW scattering. We investigate how the presence of field line boundaries affects the total HHFW power redirected into the filament, and its splitting between sheath and volume losses, as a function of relevant parameters in the model.

Keywords

fusion plasmahigh harmonic fast wave heatingplasma filamentwave scatteringmode conversionsurface wavesplasma sheaths
Type
Research Article
Information
Journal of Plasma Physics , Volume 88 , Issue 6 , December 2022 , 905880614
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Copyright
Copyright © CEA, 2022. Published by Cambridge University Press

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