Modifications in the Alfvén wave coupling contributed by the plasma equilibrium current through (i) the rotational transform, (ii) the drift induced enhanced Hall effect, and (iii) the discrete Alfvén wave excitation are studied in a model that uses a self-consistent, three-dimensional, fully analytic, Faraday shielded, periodic loop antenna and incorporates kinetic absorption effects occurring via electron Landau damping. ASDEX Upgrade parameters are employed in the computations. Among the significant changes produced by the finite rotational transform is an improved coupling (by a factor of about 2.5) at low toroidal numbers (n ∼ 1-3). Despite this gain, however, the coupling to low n continues to be poor, with R ≈ 0.03 Ω and Q ≈ 180 for n = 2. Optimum coupling, with R ≈ 0.7 Ω, occurs for n = 8 and is unaffected by the rotational transform. The safety factor of the antenna, Q ≈ 17, is comparable to that of ICRF antennas. For the large antenna configuration (n ∼ 8), mode splitting due to the removal of the poloidal degeneracy in combination with the finite electron temperature effects lead to significant broadening of the energy absorption profile. Any appreciable changes in the antenna loading, as well as an inadvertent excitation of the discrete Alfvén wave resonances due to the enhanced Hall current, are conspicuous by their absence. Direct antenna coupling to the surface shear wave is small, and no special provision such as Faraday shielding may be needed for preventing surface losses. Thus the recommendations regarding antenna design for optimum coupling to the Alfvén wave remain unaffected by the inclusion of the plasma equilibrium current.
Coupling of fast waves launched into the JFT-2M tokamak by a phased four-loop antenna array