Pfc/ja-83-40 Coupling Theory for Icrf Heating of Large Tokamaks

An analytical and numerical study for the coupling of a current sheet antenna to a tokamak plasma is presented. The antenna is of finite poloidal and toroidal dimensions and screened from the plasma by a sheath of anisotropic conductivity that shorts out just the toroidal component of the rf field. The excitation of only the fast component of the waves in the ion-cyclotron range of frequencies (ICRF) is considered. The plasma in the coupling region is described by its cold dielectric tensor with density and magnetic field inhomogeneities. The inclusion of the finite poloidal extent of the antenna introduces interesting behavior in the plasma impedance; the calculated radiation resistance is enhanced over that obtained by ignoring the poloidal variations. The coupling is better for gradual density gradients near the antenna, and the radiation resistance is dependent on the frequency of the antenna current. A set of appropriately phased poloidal antennas couple more power into the plasma than a single antenna of the same dimensions would. The power delivered into the plasma is reasonably well focussed. All this is illustrated with numerical results using parameters for a large tokamak.