Toroidal and scattering effects on lower-hybrid wave propagation

Abstract

The effects of toricity and density fluctuations on the propagation of lower‐hybrid waves are studied. These effects result mainly from changes in k_∥ as the wave propagates (k_∥ is the wavenumber parallel to the applied magnetic field). With respect to toroidal effects, k_∥ changes due to the nonconstancy of the poloidal mode number in toroidal geometry. Using ray tracing techniques, an assessment of this toroidal effect has been made. It is found that waves, which on the basis of the cylindrical geometry theory would be inaccessible, may actually propagate to the plasma center and damp. The result is related to the onset of ray ergodicity. Further, it is shown that for accessible waves the optimal poloidal launch point is near the top or bottom of the torus. In order to include the effects of density fluctuations, an electromagnetic wave kinetic equation is derived and solved by a Monte Carlo technique. It is found that scattering can further enhance accessibility.