FMCW reflectometry for measuring edge density profiles in two channels operating in 18–28 GHz and 26–40 GHz frequency ranges has been established at the Institute for Plasma Research. The reflectometer was operated in O-Mode with its horn antennae placed outside the vacuum vessel. The diagnostics were calibrated in the laboratory and also verified in-situ. A signal processing algorithm was developed to filter the noise and frequencies other than those due to the plasma. An algorithm to remove amplitude variations is used on the raw baseband signal after which the group delay is estimated using the spectrogram technique. The Bottolier-Curtet method is used for profile inversion after correcting the measured group delay for contributions to it other than plasma. First ever measurements of edge density profiles on the Aditya-U tokamak are presented which show qualitative agreement with microwave interferometer diagnostic results.
This paper describes the development and calibration of a Frequency-Modulated Continuous-Wave (FMCW) reflectometry system to measure edge density profiles in the Aditya-U tokamak. The system uses two frequency channels and signal processing algorithms to filter noise and extract the plasma density profile.