The time evolution of the electron distribution function under the action of lower hybrid waves is studied by means of the quasilinear theory. A model spectrum is assumed for the lower hybrid waves, and the dependence of the resulting lower hybrid diffusion coefficient on the electron temperature, electron density, and ambient magnetic field is investigated. A set of parameters typical of small tokamaks is utilized in a numerical analysis, and the dynamics of the formation of an electron tail is investigated. The outcome is a nearly linear dependence between current density and wave power. The transient state after the sudden disappearance of the driving wave is also illustrated.
Quasi-linear effects on the absorption of electron cyclotron waves by lower hybrid produced electron tails in tokamak plasmas