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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4308-4319 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A high-density helicon discharge (ne≤1020 m−3) produced through a new m=1 helical antenna is investigated. Various diagnostics are applied to measure the discharge parameters and the radio frequency (rf) quantities like the plasma resistance and the rf field distribution. Special attention is paid to the axial asymmetry of the discharge, which is characteristic for helicon devices with helical antennas. The axial profiles of the rf wave fields, as well as the energy deposition profiles, reveal that the rf power is mainly transferred and absorbed via the m=+1 helicon mode traveling in the positive magnetic-field direction. The experimental findings are compared with numerical results obtained from a fully electromagnetic model, which takes into account the rf current distribution of the launching antenna, as well as the finite size of the plasma column. The antenna–plasma coupling, as well as the total rf power deposited in the plasma, can be explained satisfactorily if the measured profiles are taken in the computations. In particular, the axial asymmetry of the helicon discharge can be understood in terms of the radial inhomogeneity of the plasma column. Furthermore, the calculations show that the small-scale Trivelpiece–Gould waves may be excited near the plasma edge. These waves would carry a considerable fraction of the absorbed rf power and may thus be important for the rf power coupling. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1052-1058 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of the density gradient on the dispersion of the m=+1 and m=−1 helicon modes is investigated both theoretically as well as numerically. In particular, attention is focussed on the helicon wave damping that is closely related to the rf power absorption and the Poynting flux. It is shown that the propagation characteristics of the m=−1 mode changes drastically when the density gradient is sufficiently strong. This mode exhibits a cutoff that depends on the gradient scale length and the plasma parameters. In the regime where both helicon modes propagate, the excitation of the m=−1 mode is unlikely as it is strongly damped. The results give evidence that the density gradient effect is decisive for the formation of helicon discharges, which are predominantly sustained by the m=+1 mode. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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