The suprathermal electron cyclotron radiation is used to investigate fundamental phenomena governing electron tail formation during lower hybrid current drive (LHCD). To this end, an approximate analytical solution of the 2-D time-dependent Fokker-Planck equation is developed. Electron cyclotron emission (ECE) is analysed with this model. The pitch-angle scattering time, the characteristic time of the quasi-linear diffusion process, the perpendicular temperature and the quasi-linear diffusion coefficient are measured by fitting the temporal evolution of the ECE si,signal. (C) 2001 Elsevier Science B.V. All rights reserved.