Microwave reflectometry is an established tool for the plasma profile measurements and fluctuation study, routinely utilized on many plasma confinement devices[1]. In this paper we present a theoretical model of single-frequency microwave reflectometry of plasma density fluctuations with the objective of quantitative estimation of their poloidal spectrum shape and amplitude. The model is based on the analytical solution of the full-wave equation for O-mode microwave propagation inside the plasma in the Born approximation. The plasma profile is represented as a number of cylindrical layers with the density, gradient and curvature corresponding to real plasma in the JT-60U tokamak in the reflectometer-illuminated area. The solution allows us to find explicitly the poloidal spectrum of weak plasma fluctuations. With the additional assumption of 2D isotropic spectrum in the r-θ plane it is also possible to find the fluctuation amplitude. We illustrate our model by the analysis of real signals recorded by the O-mode reflectometer on the JT-60U device [2].

References