Ray tracing of lower hybrid waves in axially inhomogeneous plasmas

Abstract

Ray tracing is performed in a ‘straight tokamak’ geometry in the presence of a axially inhomogeneous density profile to emulate tokamaks that lack toroidal symmetry (due, e.g., to density fluctuations). It is found that the toroidal mode number conservation is violated only to an extent comparable to the toroidal density homogeneity. The n∥ upshifting accordingly occurs even in the absence of symmetry in substantially the same manner as in the presence of symmetry. But the upper bound to upshifting that exists in the presence of symmetry under some conditions also exists in the absence of symmetry, and prevents bridging of large spectral gaps and wave damping.