On the influence of 2D inhomogeneity on electromagnetic mode conversion near the cut-off surfaces in magnetized plasmas

Peculiarities of the ordinary to extraordinary wave conversion in the electron cyclotron frequency range near the cut-off surfaces in magnetized plasmas are analysed in a two-dimensionally inhomogeneous simplified tokamak-like geometry. It is demonstrated that the mode conversion may be of essentially two-dimensional nature even neglecting the curvature of the cut-off surfaces; for the latter case a set of reduced wave equations in the transformation region is derived and solved analytically. Transformation coefficients for quasi-optical beams with a finite transverse distribution of rf field are obtained as well as a recipe for synthesis of the optimal ( perfectly converted) beam. Applicability limits of a conventional one-dimensional theory are finally discussed.