Development of Q-band X-mode microwave reflectometry for the measurement of edge density profile

A Q-band X-mode homodyne microwave reflectometry has been developed for the measurement of edge electron density profile on the Joint TEXT tokamak (J-TEXT). A voltage controlled oscillator (VCO) with a frequency quadrupler is used as the microwave source. An arbitrary waveform generator (AWG) is adopted to control the sweeping period (20 μs) for the VCO. Homodyne method is chose to simplify the structure of the hardware circuit. In addition, a single antenna scheme which using a directional coupler to realize the sharing of an antenna for transmitting and receiving to save the resources of diagnostic windows has been adopted. For the data processing, the Hilbert transform has been used to demodulate the signal instead of the I/Q phase detector. This reflectometry has been installed on J-TEXT and effectively measured edge density profile.