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Title: Demonstration of Electron-Bernstein-Wave Heating in a Tokamak via O-X-B Double-Mode Conversion

Abstract

The first demonstration of electron-Bernstein-wave heating by double-mode conversion from the O to the X mode in an overdense H-mode tokamak plasma has been achieved in the Tokamak a Configuration Variable device. This technique overcomes the upper density limit experienced by conventional microwave heating. The sensitive dependence of the O-X mode conversion on the microwave launching direction has been verified experimentally, and localized power deposition consistent with theoretical predictions has been observed at densities well above the conventional cutoff.

Authors:
; ; ; ; ; ;  [1]; ;  [2]
  1. Ecole Polytechnique Federale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas, Association EURATOM, CH-1015 Lausanne (Switzerland)
  2. Max-Planck-Institut fuer Plasmaphysik, EURATOM Assoziation, D-17491 Greifswald (Germany)
Publication Date:
OSTI Identifier:
20951279
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 98; Journal Issue: 17; Other Information: DOI: 10.1103/PhysRevLett.98.175004; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BERNSTEIN MODE; ELECTRONS; H-MODE PLASMA CONFINEMENT; MICROWAVE HEATING; MODE CONVERSION; PLASMA; PLASMA WAVES; TOKAMAK DEVICES

Citation Formats

Mueck, A., Curchod, L., Camenen, Y., Coda, S., Goodman, T. P., Pochelon, A., Porte, L., Laqua, H. P., and Volpe, F. Demonstration of Electron-Bernstein-Wave Heating in a Tokamak via O-X-B Double-Mode Conversion. United States: N. p., 2007. Web. doi:10.1103/PHYSREVLETT.98.175004.
Mueck, A., Curchod, L., Camenen, Y., Coda, S., Goodman, T. P., Pochelon, A., Porte, L., Laqua, H. P., & Volpe, F. Demonstration of Electron-Bernstein-Wave Heating in a Tokamak via O-X-B Double-Mode Conversion. United States. doi:10.1103/PHYSREVLETT.98.175004.
Mueck, A., Curchod, L., Camenen, Y., Coda, S., Goodman, T. P., Pochelon, A., Porte, L., Laqua, H. P., and Volpe, F. Fri . "Demonstration of Electron-Bernstein-Wave Heating in a Tokamak via O-X-B Double-Mode Conversion". United States. doi:10.1103/PHYSREVLETT.98.175004.
@article{osti_20951279,
title = {Demonstration of Electron-Bernstein-Wave Heating in a Tokamak via O-X-B Double-Mode Conversion},
author = {Mueck, A. and Curchod, L. and Camenen, Y. and Coda, S. and Goodman, T. P. and Pochelon, A. and Porte, L. and Laqua, H. P. and Volpe, F.},
abstractNote = {The first demonstration of electron-Bernstein-wave heating by double-mode conversion from the O to the X mode in an overdense H-mode tokamak plasma has been achieved in the Tokamak a Configuration Variable device. This technique overcomes the upper density limit experienced by conventional microwave heating. The sensitive dependence of the O-X mode conversion on the microwave launching direction has been verified experimentally, and localized power deposition consistent with theoretical predictions has been observed at densities well above the conventional cutoff.},
doi = {10.1103/PHYSREVLETT.98.175004},
journal = {Physical Review Letters},
number = 17,
volume = 98,
place = {United States},
year = {Fri Apr 27 00:00:00 EDT 2007},
month = {Fri Apr 27 00:00:00 EDT 2007}
}
  • The ordinary-extraordinary-Bernstein-mode conversion process for overdense plasma heating with electron-Bernstein waves is demonstrated in the WEGA stellarator at low magnetic field ({approx}50 mT) at 2.45 GHz. For the first time the conversion from an O wave to an X wave is clearly demonstrated by probe measurements of amplitude and phase of the wave field in the conversion region and supported by two-dimensional full-wave calculations. The propagation and resonant absorption of the Bernstein wave is measured in fast power modulation experiments.
  • In the large helical device (LHD), the theoretically predicted width of the ordinary-extraordinary-electron Bernstein wave (O-X-B) mode conversion (MC) window is comparable to the beam width and the power deposition is located in the off-axis region if the 77GHz fundamental electron cyclotron (EC) wave of is launched from an existing horizontal port antenna. In the experiment, the actual MC window location was looked for with changing the aiming. The effective aiming with that the increase of the stored energy was observed was two degrees apart from the location of the theoretical MC window at a maximum. Measurement of the wavesmore » originated from the thermally emitted EBW and radiated via the B-X-O mode conversion process is effective to improve the accuracy of the theoretical prediction with comparison between the theoretical and the experimental results. The theoretical prediction suggests that the width of the MC window of the fundamental 77GHz EC wave can be expanded if the lower port antenna is used. On the other hand, the MC window of the second harmonic 154GHz EC wave is blocked by horizontal port wall if another horizontal port antenna is used. It is required to move the final mirror of the quasi-optical antenna toward the plasma surface. Focusing of the beam at the plasma cutoff is (PC) also necessary for the effective mode conversion.« less
  • The first successful high power heating of a high dielectric constant spherical tokamak plasma by an electron Bernstein wave (EBW) is reported. An EBW was excited by mode conversion (MC) of an X mode cyclotron wave injected from the low magnetic field side of the TST-2 spherical tokamak. Evidence of electron heating was observed as increases in the stored energy and soft x-ray emission. The increased emission was concentrated in the plasma core region. A heating efficiency of over 50% was achieved, when the density gradient in the MC region was sufficiently steep.
  • Highly localized direct electron heating [full width at half-maximum (FWHM){congruent}0.2a] via mode converted ion Bernstein waves has been observed in the Alcator C-Mod Tokamak [I. H. Hutchinson {ital et al.}, Phys. Plasmas {bold 1}, 1511 (1994)]. Electron heating at or near the plasma center (r/a{ge}0.3) has been observed in H({sup 3}He) discharges at B{sub 0}=(6.0{endash}6.5)T and n{sub e}(0){congruent}1.8{times}10{sup 20}m{sup {minus}3}. [Here, the minority ion species is indicated parenthetically.] Off-axis heating (r/a{ge}0.5) has also been observed in D({sup 3}He) plasmas at B{sub 0}=7.9T. The concentration of {sup 3}He in these experiments was in the range of n{sub 3{sub He}}/n{sub e}{congruent}(0.2{endash}0.3) andmore » the locations of the mode conversion layer and electron heating peak could be controlled by changing the {sup 3}He concentration or toroidal magnetic field (B{sub 0}). The electron heating profiles were deduced using a rf modulation technique. Detailed comparisons with one-dimensional and toroidal full-wave models in the ion cyclotron range of frequencies have been carried out. One-dimensional full-wave code predictions were found to be in qualitative agreement with the experimental results. Toroidal full-wave calculations indicated the importance of volumetric and wave focusing effects in the interpretation of the experimental results. {copyright} {ital 1997 American Institute of Physics.}« less
  • The extension of the experimentally accessible plasma densities with electron cyclotron heating beyond the plasma cutoff density and the removal of the restriction to a resonant magnetic field, both via mode conversion heating from an O-wave to an X-wave and, finally, to an electron Bernstein (O-X-B) wave, was investigated and successfully demonstrated at the W7-AS stellarator. In addition to the heating effect, clear evidence for both mode conversion steps was detected for the first time. {copyright} {ital 1997} {ital The American Physical Society}