Nonlinearity in parametric instabilities during the injection of lower hybrid waves into tokamak plasmas

Nonlinear kinetic theory of parametric instabilities is developed and applied to study the parametric process during the injection of lower hybrid waves into tokamak plasmas. Four approaches containing different nonlinear terms are numerically solved and compared. For the resonant mode decay, the quasi-linear treatment is enough for the daughter branches. However, for the quasi-mode decay, the contribution from the nonlinear response of quasi-mode should be included in the governing equations of the sidebands. The results with correct nonlinear terms can recover those from the usually used fluid-kinetic hybrid approach in the electrostatic limit, but the kinetic theory and its simplification method developed here could be more generally applied to study parametric instabilities within the full electromagnetic framework. Published under license by AIP Publishing.