On the parasitic absorption in FWCD experiments in JET ITB plasmas

T. Hellsten, M. Laxåback, T. Bergkvist, T. Johnson, F. Meo, F. Nguyen, C.C. Petty, M. Mantsinen, G. Matthews, J.-M. Noterdaeme, T. Tala, D. Van Eester, P. Andrew, P. Beaumont, V. Bobkov, M. Brix, J. Brzozowski, L.-G. Eriksson, C. Giroud, E. JoffrinV. Kiptily, J. Mailloux, M.-L. Mayoral, I. Monakhov, R. Sartori, A. Staebler, E. Rachlew, E. Tennfors, A. Tuccillo, A. Walden, K.-D. Zastrow

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Fast wave current drive (FWCD) experiments have been performed in JET plasmas with electron internal transport barriers produced with LHCD. Because of a large fraction of parasitic absorption, owing to weak single pass damping, the inductive nature of the plasma current and the interplay between the RF-driven current and the bootstrap current only small changes are seen in the central current profiles. The measured difference in the central current density for co- and counter-current drive is larger than the response expected from current diffusion calculations, but smaller than the driven currents, suggesting a faster current diffusion than that given by neo-classical resistivity. A large fraction of the power is absorbed by cyclotron damping on residual 3He ions while a significant fraction appears not to have been deposited in the plasma. The strong degradation of heating and current drive occurs simultaneously with strong increases in the Be II and C IV line intensities in the divertor. The degradation depends on the phasing of the antennas and increases with reduced single pass damping which is consistent with RF-power being lost by dissipation of rectified RF-sheath potentials at the antennas and walls. Asymmetries in direct electron heating, lost power and production of impurities, fast ions and gamma-rays are seen for co- and counter-current drive. These differences are consistent with the differences in the absorption on residual 3He ions owing to the RF-induced pinch. Effective direct electron heating, comparable to the indirect electron heating with H-minority heating, occurs for dipole phasing of the antennas without producing a significant fast ion pressure and with low impurity content in the divertor plasma. © 2005 IAEA, Vienna.
Original languageEnglish
Pages (from-to)706 - 720
Number of pages15
JournalNuclear Fusion
Issue number7
Publication statusPublished - 1 Jul 2005
Externally publishedYes


All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics
  • Condensed Matter Physics

Cite this

Hellsten, T., Laxåback, M., Bergkvist, T., Johnson, T., Meo, F., Nguyen, F., ... Zastrow, K-D. (2005). On the parasitic absorption in FWCD experiments in JET ITB plasmas. Nuclear Fusion, 45(7), 706 - 720. https://doi.org/10.1088/0029-5515/45/7/020