Electron density profile reconstruction on the TCABR sweeping reflectometer

Abstract

A Frequency Sweeping Reflectometry System is under re-installation in the TCABR tokamak to provide the electron density profiles in this machine. This diagnostic operates in a frequency range between 18 GHz and 40 GHz, in Ordinary (O-mode) or in Extraordinary (X-mode) polarization modes. This diagnostic can cover electron densities between 0.4×1019m-3 and 2.0×1019m-3, when configured in O-mode. Electron density profiles can be inferred from the phase dependence of the probing frequency, dΦ(f)/df, measured at the output of the reflectometer system. To evaluate the measuring capabilities and the requirements for using a frequency sweeping reflectometer, a numerical method to reconstruct the density profiles in the TCABR tokamak was implemented. The robustness of inversion method was tested through the following steps: i) Determination of dΦ(f)/df from a known density profile; ii) Reconstruction of the electron density profile by the method that will be presented here; iii) Comparison between the original and reconstructed electron density profiles to test the validity of the method. The method and analysis are applied for the X and O polarization modes. These computational analyses can be useful for the interpretation of reflectometer diagnostic data and the experimental data can be used to check the validity of the numerical model.