Development Of Q-band Reflectometry On The Joint TEXT Tokamak

Microwave diagnostic is an essential tool to get experimental data for magnetic confinement fusion research. The microwave reflectometry is a radar-like method for the measurement of electron density profile in inhomogeneous plasma. This article mainly introduces the development of the Q-Band(33-50GHz) ordinary mode(O-mode) fast sweep frequency modulated continuous wave(FMCW) reflectometry.Started from the research background, firstly the article introduces the categories, advantages, development history and research status of the reflectometry. After the description of the basic principle, a Q-Band O-mode reflectometry has been designed based on the relevant parameters of J-TEXT, corresponding to the measured density 1.366×1019 m-3 to 3.136×1019 m-3.The reflectometry incidents waves into plasma from 32 GHz to 50 GHz with sweep period of 20?s. A 60M/s data acquisition card is selected to get the beat frequency from the I/Q detector, which is processed with the short-time Fourier transform method.Experimentally, we have done something to enhance the performance of the system. A Yttrium Iron Garnet(YIG) filter is adopted for the dynamic calibration of the voltage controlled oscillator(VCO) to obtain the frequency characteristic more accurately. The adoption of the power combiner helps to suppress the image frequency of the single side-band modulator(SSBM). In that way the incident wave is more powerful, which enhances the signal-noise ratio as well as decreases the deleterious effects of the amplitudes changes of the reflected wave. A 2.5m-long delay line is finally adjusted to compensate the phase shift caused by the microwave circuit.The bench test has been done to prove the availability and accuracy of the reflectometry. During the experiments in 2015, the results from reflectometry shows a great agreement with the one from polarimeter. And it has been applied to some physical studies.