DIRECT ANTENNA EXCITATION OF THE SHEAR ALFVEN-WAVE AT FINITE FREQUENCY IN THE BOUNDARY OF A FUSION PLASMA

The problem of direct excitation of the shear Alfven wave by antennas in the boundary of a fusion plasma is considered. In the plasma scrape -off layer the physics of this wave is determined by finite electron i nertia. Expressions for the wave electric and magnetic field are deriv ed without any assumption on the smallness of the ratio of frequency t o ion cyclotron frequency. It is shown that the shear Alfven wave prop agates as a guided beam along the steady magnetic field over a wide ra nge of frequencies below the ion cyclotron frequency, and is predomina ntly excited by current elements parallel to the steady magnetic field . A simple transmission-line analogy suggests that guidance of the Alf ven wave is also expected in the presence of strong plasma inhomogenei ty.