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, Tuomas 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, JET-EFDA Contributors

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    Abstract

    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.
    Original languageEnglish
    Pages (from-to)706 - 720
    Number of pages15
    JournalNuclear Fusion
    Volume45
    Issue number7
    DOIs
    Publication statusPublished - 2005
    MoE publication typeA1 Journal article-refereed

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    Keywords

    • JET
    • plasma
    • fusion energy
    • fusion reactors
    • ITER
    • Tokamak
    • internal transport barriers

    Cite this

    Hellsten, T., Laxåback, M., Bergkvist, T., Johnson, T., Meo, F., Nguyen, F., Petty, C. C., Mantsinen, M., Matthews, G., Noterdaeme, J-M., Tala, T., Van Eester, D., Andrew, P., Beaumont, P., Bobkov, V., Brix, M., Brzozowski, J., Eriksson, L-G., Giroud, C., ... JET-EFDA Contributors (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