STUDY OF THE PARAMETRIC INSTABILITIES IN THE LOWER HYBRID FREQUENCY RANGE IN THE FT TOKAMAK
An overall view of the phenomenology observed with radio-frequency (RF) probes during lower hybrid wave injection is presented for several operational regimes of the FT tokamak. We mainly focussed on the high plasma density regime where the effects of the launched waves on the main plasma become negligible. A rather rich spectrum from about O MHz to beyond the injected frequency is observed in response to the RF pulse. Many secondary peaks, or sidebands, shifted from the pump by multiples of the ion cyclotron frequency evaluated at the outer torus edge appear, while the pump spectrum is strongly broadened. Evidence of the primary importance of the border plasma conditions is recognized. Using a numerical code, we satisfactorily reproduced part of the experimental data concerning the decay process which originates the sideband. We considered the decay of the pump into a quasi mode strongly damped on ions and took into account the convection losses due to the finite extension of the pump. The key to the good agreement between the numerical simulations and the experiment was to attribute a pre-eminent role to the plasma edge and to its variation with the main plasma parameters, i.e., density and current.
Bibliographic Reference: WRITE TO SERVIZIO STUDI E DOCUMENTAZIONE - ENEA, CENTRO RICERCHE ENERGIA FRASCATI, C.P. 65 - 00044 FRASCATI, ROMA (ITALY), MENTIONING REPORT RT/FUS/865, 1986
Record Number: 1989125048800 / Last updated on: 1987-07-01
Available languages: en