Design of Q-band FMCW reflectometry for electron density profile measurement on the Joint TEXT tokamak

The Q-band (33–50 GHz) fast sweep frequency modulated continuous wave (FMCW) reflectometry has been recently developed for electron density profile measurement on the Joint TEXT tokamak. It operates in ordinary mode (O-mode) with a 20 μs sweeping period, covering the density range from 1×10¹⁹m⁻³ to 3×10¹⁹ m⁻³. On the bench test, a Yttrium Iron Garnet (YIG) filter is used for the dynamic calibration of the voltage controlled oscillator (VCO) to obtain a linear frequency sweep. Besides, the use of a power combiner helps to improve the sideband suppression level of the single side-band modulator (SSBM). The reconstructed density profiles are presented, which demonstrate the capability of the refiectometry.