Parametric Heating by Radio-Frequency near the Lower Hybrid Frequency in the JFT-2 Tokamak

Abstract

Ion heating efficiencies of the central plasma obtained under various experimental conditions indicated that a nonlinear effect played an important role in the ion heating when the high rf power was irradiated to the plasma. Nonlinearly excited electromagnetic modes as well as the parametric decay spectrum of the electrostatic modes, which were also observed simultaneously, sugegested a further excitation of nonresonant quasi-modes decay instability. It wins shown that the ion heating for ω₀⁄ω_1h(0)\gtrsim1.13 (where ω₀ is frequency of irradiated rf field and ω_1h(0) is the lower hybrid frequency at the center of the plasma column) were well explained by the theoretical model having the empirical nonlinear heating rates resulting from the excitation of nonresonant quasi-modes in one-dimensional WKB approximation.