THE EFFECT OF POLOIDAL ANTENNA WIDTH ON LOWER-HYBRID RAY-PROPAGATION

In simulations of lower hybrid heating and current drive in tokamaks, an important part of the calculation is the determination of ray paths from the antenna to the central region of the plasma where they are absorbed. The role of the parallel refractive index spectrum and the need to launch a set of rays that cover it adequately are well known. However, the antenna also has a finite poloidal extent and a corresponding poloidal wavenumber spectrum. Here a method of estimating the effect of this poloidal structure on the spatial and spectral widths of the beam is discussed. The objective is to take this into account without the need to launch a set of rays covering the range of poloidal positions and wavenumbers as well as that of parallel wavenumbers.