Absorption and mode conversion of fast waves at high ion cyclotron harmonics in the helicon frequency range

Recently there has been considerable interest in using fast waves in the helicon frequency range, which corresponds to high ion cyclotron harmonics, for off-axis current drive in tokamaks. The hot plasma dispersion relation shows that the ion Bernstein mode can propagate on the high field side of the harmonic resonance. The launched fast wave can be converted into the Bernstein mode and be absorbed near the resonance layer. In this work, absorption and mode conversion of the fast wave are examined with an one dimensional wave equation, which is converted from the dispersion relation by taking the inverse Fourier transform. In obtaining the relevant equation the hot plasma dispersion relation is cast into a form without any sums using the method of steepest descents and then it is approximated by polynomials in the perpendicular wave number.