Nonlinear Coupling of Lower-Hybrid Waves at the Edge of Tokamak Plasmas

We solve the steady-state coupling problem of lower-hybrid waves excited by a wave-guide array. The theory takes into account the ponderomotive density modulation to all orders in the electric field amplitude but assumes that the nonlinear effects are important only along the magnetic field lines. The important new feature is the appearance of a resonant term in the transverse refractive index, which is due to the finite size of the excitation structure. A calculation for two waveguides, linear density profile, and constant temperature is presented.