Plasma production by helicon waves with single mode number in low magnetic fieldsReport as inadecuate

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1 Hatakeyama Laboratory

Abstract : The helicon waves are of considerable interest because they have been found to be very effective in creating high plasma densities. The density peak is observed in a certain low magnetic field ~5 mT in many experiments of helicon-wave discharge but its details are not made clear sufficiently. It is important to elucidate the physical mechanism of the density peak from the standpoint of the development of efficient plasma sources. We have investigated the physical mechanism of the density peak using several antennas with azimuthal mode-number m=1. Two ordinary antennas for helicon-wave excitation with m=1, half-helical antenna and double-half-turn antenna, and our original multiple-helical antenna are found to give rise to the density peak, respectively. The density peak appears in the cases of the half-helical antenna and the multiple-helical antenna when the amplitude of the helicon wave excited is large and the wavelength calculated from the density and the magnetic field in the plasma is close to the axial antenna-length. Therefore the plasma parameters for the density peak are inherently determined by the axial antenna-length. Helicon waves with not only m=+1 but also m=-1 can be selectively excited by only the multiple-helical antenna. The density peak also appears with m=-1 helicon wave in low magnetic fields. Helicon wave with m=+1 can propagate in the plasma, whether the density peak appears or not. On the other hand helicon wave with m=-1 is excited only if the density peak appears. It is theoretically predicted that helicon wave with m=-1 has a cutoff in relatively low-density region in the dispersion relation under the assumption that the radial profile of the plasma has a gaussian 1, and helicon wave with m=-1 can-t exist in the condition of low density, except for the density peak.1 M. Kärmer: Phys. Plasma 6, 1999 1052

Author: Genta Sato - Wataru Oohara - Rikizo Hatakeyama -



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