The measurement of the spatial distribution of the lower-hybrid driven current in Tokamaks using electron-cyclotron wave attenuation of the ordinary mode at frequencies below the plasma frequency is discussed. It is shown that the r.f.-driven current density profile can be determined by differential transmission measurements of two equivalent rays propagating near the horizontal plane and reflected by the cut-off layer. An application to lower-hybrid current drive in JET is presented.
Up-shifted frequency electron-cyclotron current drive in a lower hybrid current drive plasma