Observation of Parametric Decay of a Pumping Wave in Lower Hybrid Wave Heating and Current Drive Experiments at the FT-2 Tokamak

Abstract

The systematization of experimental data related to development of the parametric decay instability in tokamak plasma during RF power input within the lower hybrid frequency range was performed, which allows its characteristics to be compared with theoretical representations. The spectra of pumping waves and radiation from the plasma are obtained, which illustrate the appearance of satellites that are shifted from a pump frequency by a value that is a multiple of the ion cyclotron frequencies, toward the “red” and “blue” sides. It is noted that with a rise in density, a considerable broadening of the line of a pumping wave occurs. Values of the RF power and plasma density are observed, which are threshold values for the onset of the development of parametric decay instability. Using the diagnostic complex, the analysis of the low-frequency region of the plasma oscillation spectrum was carried out. The conditions of the development of instability were analyzed within the existing theoretical representations.