Limits of applicability of the quasilinear approximation to the lower hybrid wave-plasma interaction

The diffusion of electrons in velocity space induced by a spectrum of elect rostatic waves is numerically investigated. From the scatter of particles, the diffusion coefficient is calculated and compared with the quasilinear v alue. A strong disagreement is found at high electric held amplitudes, narr ow spectra and short (spatial) lengths of the interaction region, which are however usual in Lower Hybrid Heating and Current Drive experiments in tok amaks. In particular, the (velocity) interaction region becomes significant ly broader than the Landau resonance region for electric held amplitudes ab ove similar to 10 kV m(-1).