skip to main content

SciTech ConnectSciTech Connect

Title: Radio-frequency sheath voltages and slow wave electric field spatial structure

We investigate theoretically how sheath radio-frequency (RF) oscillations relate to the spatial structure of the RF parallel electric field emitted by Ion Cyclotron (IC) wave launchers, using a simple model of Slow Wave (SW) evanescence coupled with Direct Current (DC) plasma biasing via sheath boundary conditions in a plasma-filled 2-dimensional (parallel, radial) rectangle. Within a “wide sheaths” asymptotic regime, valid for large-amplitude near RF fields, our model becomes partly linear: the sheath oscillating voltage at open field line boundaries is a linear combination of elementary contributions by every source point of the radiated RF field map. These individual contributions are all the more intense as the SW emission point is toroidally nearer to the sheath walls. A limit formula is given for a source infinitely close to the sheaths. The decay of sheath RF voltages with the sheath/source parallel distance is quantified as a function of two characteristic SW evanescence lengths. Decay lengths are smaller than antenna parallel extensions. The sheath RF voltages at an IC antenna side limiter are therefore mainly sensitive to SW emission near this limiter, as recent observations suggest. Toroidal proximity effects could also explain why sheath oscillations persist with antisymmetric strap toroidal phasing, despite themore » parallel anti-symmetry of the radiated field map. They could also justify current attempts at reducing the RF fields induced near antenna boxes to attenuate sheath oscillations in their vicinity.« less
Authors:
;  [1] ;  [2] ;  [3]
  1. CEA, IRFM, F-13108 Saint-Paul-Lez-Durance (France)
  2. LPP-ERM-KMS, TEC partner, Brussels (Belgium)
  3. Max-Planck-Institut für Plasmaphysik, Garching (Germany)
Publication Date:
OSTI Identifier:
22496200
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1689; Journal Issue: 1; Conference: 21. topical conference on radio frequency power in plasmas, Lake Arrowhead, CA (United States), 27-29 Apr 2015; Other Information: (c) 2015 EURATOM; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; AMPLITUDES; ANTENNAS; ASYMPTOTIC SOLUTIONS; BOUNDARY CONDITIONS; DECAY; DIRECT CURRENT; ELECTRIC FIELDS; ELECTRIC POTENTIAL; EMISSION; LENGTH; LIMITERS; OSCILLATIONS; PLASMA; RADIOWAVE RADIATION; TWO-DIMENSIONAL CALCULATIONS