Minority and mode conversion heating in (

D. Van Eester, E. Lerche, T.J. Johnson, T. Hellsten, J. Ongena, M.-L. Mayoral, D. Frigione, C. Sozzi, G. Calabro, M. Lennholm, P. Beaumont, T. Blackman, D. Brennan, A. Brett, M. Cecconello, I. Coffey, A. Coyne, K. Crombe, A. Czarnecka, R. FeltonM. Gatu Johnson, C. Giroud, G. Gorini, C. Hellesen, P. Jacquet, Ye Kazakov, V. Kiptily, S. Knipe, A. Krasilnikov, Y. Lin, M. Maslov, I. Monakhov, C. Noble, M. Nocente, L. Pangioni, I. Proverbio, M. Stamp, W. Studholme, M. Tardocchi, T.W. Versloot, V. Vdovin, A. Whitehurst, E. Wooldridge, V. Zoita

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Abstract

Radio frequency (RF) heating experiments have recently been conducted in JET (3He)-H plasmas. This type of plasmas will be used in ITER's non-activated operation phase. Whereas a companion paper in this same PPCF issue will discuss the RF heating scenario's at half the nominal magnetic field, this paper documents the heating performance in (3He)-H plasmas at full field, with fundamental cyclotron heating of3He as the only possible ion heating scheme in view of the foreseen ITER antenna frequency bandwidth. Dominant electron heating with global heating efficiencies between 30% and 70% depending on the3He concentration were observed and mode conversion (MC) heating proved to be as efficient as3He minority heating. The unwanted presence of both4He and D in the discharges gave rise to 2 MC layers rather than a single one. This together with the fact that the location of the high-field side fast wave (FW) cutoff is a sensitive function of the parallel wave number and that one of the locations of the wave confluences critically depends on the3He concentration made the interpretation of the results, although more complex, very interesting: three regimes could be distinguished as a function of X[3He]: (i) a regime at low concentration (X[3He]<1.8%) at which ion cyclotron resonance frequency (ICRF) heating is efficient, (ii) a regime at intermediate concentrations (1.8<X[3He]<5%) in which the RF performance is degrading and ultimately becoming very poor, and finally (iii) a good heating regime at3He concentrations beyond 6%. In this latter regime, the heating efficiency did not critically depend on the actual concentration while at lower concentrations (X[3He]<4%) a bigger excursion in heating efficiency is observed and the estimates differ somewhat from shot to shot, also depending on whether local or global signals are chosen for the analysis. The different dynamics at the various concentrations can be traced back to the presence of 2 MC layers and their associated FW cutoffs residing inside the plasma at low3He concentration. One of these layers is approaching and crossing the low-field side plasma edge when 1.8<X[3He]<5%. Adopting a minimization procedure to correlate the MC positions with the plasma composition reveals that the different behaviors observed are due to contamination of the plasma. Wave modeling not only supports this interpretation but also shows that moderate concentrations of D-like species significantly alter the overall wave behavior in3He-H plasmas. Whereas numerical modeling yields quantitative information on the heating efficiency, analytical work gives a good description of the dominant underlying wave interaction physics. © 2012 IOP Publishing Ltd.
Original languageEnglish
Article number074009
Pages (from-to)-
JournalPlasma Physics and Controlled Fusion
Volume54
Issue number7
DOIs
Publication statusPublished - Jul 2012
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Nuclear Energy and Engineering
  • Condensed Matter Physics

Cite this

Van Eester, D., Lerche, E., Johnson, T. J., Hellsten, T., Ongena, J., Mayoral, M-L., Frigione, D., Sozzi, C., Calabro, G., Lennholm, M., Beaumont, P., Blackman, T., Brennan, D., Brett, A., Cecconello, M., Coffey, I., Coyne, A., Crombe, K., Czarnecka, A., ... Zoita, V. (2012). Minority and mode conversion heating in (. Plasma Physics and Controlled Fusion, 54(7), -. [074009]. https://doi.org/10.1088/0741-3335/54/7/074009