Toroidal effects on propagation, damping, and linear mode conversion of lower hybrid waves

A common simplifying assumption made in the consideration of radio-frequency heating of tokamaks near the lower hybrid frequency is that the wavelength imposed by the coupling device parallel to the magnetic field is not modified by gradients along the field. In the present calculation, the parallel wavelength is allowed to vary, and important effects are found on wave penetration and damping if the toroidal aspect ratio (Rmajor/rminor) is less than approximately five. The calculation shows that heating at the center of a small aspect ratio torus is inhibited by a decrease in k∥ if waves are launched at the outside, and that it may be possible to change the plasma current via electron Landau damping with a coupler of symmetric power spectrum by placing the coupler at the top (or bottom) of the torus.