Applicability of the geometrical optics at the high electron cyclotron harmonics

Nearly perpendicular wave propagation across the Nth electron cyclotron harmonic layer in a weakly inhomogeneous plasma is investigated. It is shown that, when N>2, unlike the case for N< or =2, the relativistic corrections and the mode conversion to Bernstein waves do not alter the current density to the lowest significant order in the expansion parameter, which is the ratio of the electron thermal speed to the speed of light. Thus, when N>2, the geometrical optics method should be applicable in this case, and hence at all angles of incidence