Use of the multidimensional WKB method to describe propagation of lower hybrid waves in tokamak plasma

Abstract

The influence of diffraction on the propagation of lower hybrid (LH) waves in tokamak plasma was studied. This effect has not been investigated before owing to a lack of suitable methods for solving the wave equation. An asymptotic method is developed which, while using a quasi-classical description in the direction of the group velocity, retains a wave description perpendicular to that direction. This method reduces the general wave equation to a system of ordinary differential equations. It is shown that allowance for the wave properties results in significant diffractional blurring of LH wave beams. This effect occurs in both configurational space and spectral space. In the first, it causes broadening of the absorbed power profile. In the second, it enriches the spectrum with slow waves, increasing interaction with electrons. The effect of diffraction is greater than the effects of the geometrical optics usually taken into account