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During the initial experimental phase, LHD, a stellarator of the heliotron/torsatron variety presently under construction, will operate at a magnetic field lower than the nominal one. In this scenario, the frequency of the available gyrotrons will be resonant with the third or the fourth harmonic of the electron gyrofrequency. An analysis is made of the electron cyclotron resonance heating (ECRH) at these high harmonics. By using linear absorption theory, together with transport predictions, good absorption is found over a wide density range for third harmonic heating. In the case the fourth harmonic, the conditions for absorption are considerably more critical, by non-negligible heating is expected in very low density, high temperature target plasmas. Owing to the strong temperature dependence of the absorption mechanism, heating at higher harmonics presents some peculiar characteristics. Quasi-linear effects are found to improve the absorption properties and bifurcation phenomena, as well as a critical power threshold, might appear. The physical origin and the consequences of these effects are discussed.

Additional information

Authors: GASPARINO U, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE);ROMÉ M, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE);IDEI H, National Institute for Fusion Science, Nagoya (JP);KUBO S, National Institute for Fusion Science, Nagoya (JP);MARUSCHENKO N, Kharkov Institute of Physics and Technology, National Science Center, Institute of Plasma Physics (UA);ROME M, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE)
Bibliographic Reference: Article: Nuclear Fusion, Vol. 38 (1998) No. 2, pp. 223-235
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