Parametric instabilities excited by ion-sound and ion cyclotron quasi-modes in lower hybrid heating of tokamak plasmas
The parametric decays of a lower hybrid (LH) pump are studied in a wide range of low-frequency quasi-modes which drive the instabilities. The numerical results of the parametric dispersion relation show that an ion-sound quasi-mode with frequency w can excite a parametric instability with a growth rate y >= w (at the plasma edge, even at low power levels of pump wave). Solutions can be found where the two LH sidebands can be resonant within a small frequency shift and both grow in instability. The estimated convective thresholds are in the range of the rf power used for experiments on heating of tokamak plasmas. Such an instability can be related to the frequency broadening of the injected rf power observed during the LH additional heating experiments in FT and in other devices. The analysis shows that in the outer plasma region, ion-cyclotron quasi-modes can drive parametric instabilities where higher growth rates are found if a broadening of the launched parallel wave number is supposed. This kind of instability may explain the rf spectra observed during the high density plasma regimes, which show a typical nonmonotonic envelope of the sideband peaks.
Bibliographic Reference: Report: RT/FUS/87/37 EN (1987)
Availability: Available from Servizio Studi e Documentazione, ENEA, Centro Ricerche Energia Frascati, C.P. 65-00044 Frascati, Roma (IT)
Record Number: 198910600 / Last updated on: 1994-12-01
Original language: en
Available languages: en