A general variational principle for an ICRF antenna radiating into a slab plasma is presented. The model is three-dimensional and includes the effect of connections to a transmission line. It also assumes an extent of absorption in the plasma that is sufficient to suppress eigenmodes. The variational principle gives the self-consistent currents flowing in the antenna, the fields excited inside the plasma and the antenna impedance at the generator terminals. Numerical computations are made for a TFR and a JET antenna. A study of power coupling shows that the optimum operating frequency lies near the plasma-modified resonance. The fields excited inside the plasma are found to disperse far more in the toroidal than in the poloidal direction. Also, at frequencies far from resonance, the large currents in the connections excite fields of considerably larger spatial extent than at resonance.

A BSTRA CT.Launching of the fast wave in the lower hybrid frequency range is described. This wave is excited at the plasma edge by RF electric field's perpendicular to those required for the lower-hybrid wave. In high temperature plasmas, where the lower hybrid wave may not penetrate because of Landau damping or other effects near the edge, the fast wave might provide an alternative for heating and/or current generation in the central portion of the plasma. In addition, for high density plasmas this has the advantage that lower frequencies than those required for the lower hybrid excitation can be used. Thus wayeguides of convenient dimensions for maximum power transmission and ease of fabrication can be employed. Coupling from a waveguide array into an inhomogeneous plasma is analysed. Power reflection in the waveguides is found as a function of array design and density gradient at the edge. This reflection is fairly large (> 20%). Propagation into the plasma is then considered and the field structure and dispersion of the fast waves are found as a function of distance of penetration. Unlike the lower hybrid waves, fast waves do not form resonance cones and energy is dispersed over a large volume.