On possibility of low-threshold two-plasmon decay instability in 2nd harmonic ECRH experiments at toroidal devices
1 Ioffe Institute of RAS, 26 Polytekhnicheskaya st., St. Petersburg 194021, Russia
2 RLPAT, St. Petersburg State Polytechnical University, 29 Polytekhnicheskaya st., St. Petersburg 195251, Russia
The effects of the parametric decay of the 2nd harmonic X-mode into two short wave-length UH plasmons propagating in opposite directions is considered. The possibility of the absolute instability excitation is demonstrated in the case of the density profile possessing local maximum slightly exceeding the UH resonance value. The threshold of the absolute instability is shown to be substantially smaller than that provided by the standard theory for monotonous density profile.
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