Measurements of electron density profile by frequency modulated continuous wave reflectometer in the T-10 tokamak...

A new, previously unused combination of the high magnetic field side probing and the lower extraordinary mode cutoff was used in the T-10 tokamak for the electron density profile measurements by using a frequency modulation continuous wave reflectometer. This scheme has a significant advantage for large fusion machines where flat electron density profiles and high electron temperatures are expected. The reflectometer design is based on a common scheme with voltage controlled oscillators, active multipliers, and in-phase/quadrature signal detection. Iterative procedures were applied to calibrate a microwave source frequency and compensate the dispersion of probing signals in the conventional rectangular waveguides used as the transmission lines. About 0.2% stability of the beating frequency was reached after the calibration procedure had been finished. An advanced finite-difference scheme was proposed for the reconstruction of the electron density profile to reduce errors and improve the overall performance of the algorithm. Reconstructed electron density profiles demonstrate good agreement with conventional T-10 diagnostic data. Some specific technical and physical aspects of the diagnostic were also discussed on the basis of T-10 operation experience.