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Title: Lower hybrid wavepacket stochasticity revisited

Analysis is presented in support of the explanation in Ref. [1] for the observation of relativistic electrons during Lower Hybrid (LH) operation in EC pre-heated plasma at the WEGA stellarator [1,2]. LH power from the WEGA TE11 circular waveguide, 9 cm diameter, un-phased, 2.45 GHz antenna, is radiated into a B≅0.5 T, Ðœ„n{sub e}≅5×10{sup 17} 1/m{sup 3} plasma at T{sub e}≅10 eV bulk temperature with an EC generated 50 keV component [1]. The fast electrons cycle around flux or drift surfaces with few collisions, sufficient for randomizing phases but insufficient for slowing fast electrons down, and thus repeatedly interact with the rf field close to the antenna mouth, gaining energy in the process. Our antenna calculations reveal a standing electric field pattern at the antenna mouth, with which we formulate the electron dynamics via a relativistic Hamiltonian. A simple approximation of the equations of motion leads to a relativistic generalization of the area-preserving Fermi-Ulam (F-U) map [3], allowing phase-space global stochasticity analysis. At typical WEGA plasma and antenna conditions, the F-U map predicts an LH driven current of about 230 A, at about 225 W of dissipated power, in good agreement with the measurements and analysis reported in [1].
Authors:
; ; ; ; ;  [1] ;  [2]
  1. Institute of Plasma Physics AS CR, v.v.i., Prague, CZ, Association EURATOM/IPP.CR (Czech Republic)
  2. Max Planck Institute für Plasmaphysik, EURATOM Association, D-17491 Greifswald (Germany)
Publication Date:
OSTI Identifier:
22264090
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 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANTENNAS; APPROXIMATIONS; COLLISIONS; ELECTRIC FIELDS; ELECTRONS; EQUATIONS OF MOTION; LOWER HYBRID CURRENT DRIVE; LOWER HYBRID HEATING; PHASE SPACE; PLASMA; RELATIVISTIC RANGE; WAVE PACKETS; WEGA STELLARATOR