Modeling the spectral modification of lower hybrid wave in the presence of drift-wave type density fluctuation in the scrape-off-layer of the EAST tokamak

Abstract

The spectrum change of the lower hybrid (LH) waves caused by a low-frequency density fluctuation in the scrape-off-layer is studied by applying the wave scattering model developed by Bonoli and Ott [Phys. Fluids 25, 359 (1982)] via a Monte Carlo method. Due to the influence of the density fluctuation, the perpendicular component of the LH wave-vector can be rotated in the 2D perpendicular space, which will further change the ray trajectory of the LH wave. A ray-tracing model specific to this purpose is developed to evaluate the probability distribution of both the poloidal refractive index (Nθ) and the parallel refractive index ( N∥) of the LH wave at the last closed flux surface (LCFS). The scattering probability and the rotation scattering angle are determined by the combined effect from the geometric optics approximation term and the E×B drift term in the LH tensor elements. The probability distributions of N∥ and Nθ at the LCFS are studied using the EAST parameters as a function of wave frequency, the initial N∥, and the polar injection position, which may influence the lower hybrid current drive efficiency.