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Title: RF physics of ICWC discharge at high cyclotron harmonics

Recent experiments on Ion Cyclotron Wall Conditioning (ICWC) performed in tokamaks TEXTOR and ASDEX Upgrade with standard ICRF antennas operated at fixed frequencies but variable toroidal magnetic field demonstrated rather contrasting parameters of ICWC discharge in scenarios with on-axis fundamental ion cyclotron resonance (ICR) for protons,ω=ω{sub H+}, and with its high cyclotron harmonics (HCH), ω=10ω{sub cH+}⋅ HCH scenario: very high antenna coupling to low density RF plasmas (P{sub pl}≈0.9P{sub RF-G}) and low energy Maxwellian distribution of CX hydrogen atoms with temperature T{sub H}≈350 eV. Fundamental ICR: lower antenna-plasma coupling efficiency (by factor of about 1.5 times) and generation of high energy non-Maxwellian CX hydrogen atoms (with local energy E{sub ⊥H} ≥1.0 keV). In the present paper, we analyze the obtained experimental results numerically using (i) newly developed 0-D transport code describing the process of plasma production with electron and ion collisional ionization in helium-hydrogen gas mixture and (ii) earlier developed 1-D Dispersion Relation Solver accounting for finite temperature effects and collision absorption mechanisms for all plasma species in addition to conventionally examined Landau/TTPM damping for electrons and cyclotron absorption for ions. The numerical study of plasma production in helium with minor hydrogen content in low and high toroidal magnetic fieldsmore » is presented. The investigation of the excitation, conversion and absorption of plasma waves as function of B{sub T}-field suggests that only fast waves (FW) may give a crucial impact on antenna coupling and characteristics of the ICWC discharge using standard poloidally polarized ICRF antennas designed to couple RF power mainly to FW. The collisional (non-resonant) absorption by electrons and ions and IC absorption by resonant ions of minor concentration in low T{sub e} plasmas is studied at fundamental ICR and its high harmonics.« less
Authors:
; ; ; ;  [1] ; ; ;  [2] ; ;  [3] ; ; ; ;  [4] ;  [5] ;  [6] ; ;
  1. Association Euratom-Belgian State, LPP-ERM-KMS, 1000 Brussels (Belgium)
  2. Association Euratom-IPP, Max-Planck Institut für Plasmaphysik, 85748 Garching (Germany)
  3. Association Euratom-CEA, CEA, IRFM, 13108 St Paul lez Durance (France)
  4. Association Euratom-IEK-4, Forschungszentrum Jülich, 52425 Jülich (Germany)
  5. Institute of Plasma Physics NSC KIPT, 61108 Kharkiv (Ukraine)
  6. Association Euratom-IPP, Max-Planck Institut für Plasmaphysik, 85748 Garching, Germany and Ghent University, 9000 Ghent (Belgium)
Publication Date:
OSTI Identifier:
22263866
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1580; Journal Issue: 1; Conference: 20. topical conference on radiofrequency power in plasmas, Sorrento (Italy), 25-28 Jun 2013; Other Information: (c) 2014 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ABSORPTION; ANTENNAS; ASDEX TOKAMAK; COUPLING; CYCLOTRON HARMONICS; CYCLOTRONS; DENSITY; HYDROGEN; ICR HEATING; ION CYCLOTRON-RESONANCE; IONS; MAGNETIC FIELDS; NUMERICAL ANALYSIS; PLASMA PRODUCTION; PLASMA WAVES; TEMPERATURE DEPENDENCE; TEXTOR TOKAMAK