Microwave Reflectometry In Magnetic Confinement Of Plasma Applications

The thesis is basic on research of microwave reflectometry, the microwave re-flectometer is a diagnosis equipment and it can provide the plasma density profile and plasma Density fluctuation in magnetic confinement devices, benefit from its high tem-poral and spatial resolution and relatively small window consuming, it has been widely used in a lot of magnetic confinement devices around the world.The main work of this thesis was arranged as follow:microwave reflectometer scheme design, microwave re-flectometer table experiment research, microwave reflectometry data analysis method, microwave reflectometry experiment measurements at tokamak.Through the table ex-periment research, we can indicate key parameters of microwave reflectometer such as:measurement target, electron density range, temporal and spatial resolution, range resolution, range accuracy.At first, the thesis introduce three kinds of microwave reflectometer scheme, which includ amplitude modulation reflectometry, frequency modulated continuous wave reflectometry, pulse radar reflectometry.At EAST tokamak,frequency modula-tion was chosen as the reflectometry schematic, HTO was utility as reflectometry source, the reflectometry can sweep the full band in ten microseconds, plasma can be seen as ’frozen’ in the sweep period. In order to increase the plasma density cov-erage, the transmit antenna was arranged45degree with magnetic field, extraordinary wave and extraordinary wave polarization antenna were utility as received antenna. The reflectometer frequency range cover33GHz～72GHz, so corresponding elec-tron density measurement range is0～6.0×1019m-3. which makes the reflectometer can cover the low field side plasma at EAST Tokamak.In the thesis, several parameters which can affect reflected signal has been re-searched at table experiment. The parameters include:the output frequency character-istics of microwave source,Sweep rate of the microwave source, the distance between the transmit and receive antenna, angle between antenna and metal panel, the disper-sion effect at waveguide. By adjusting these parameters in table experiment, we can observer beat frequency spectrum, according to table experiment result, we can con- firm spatial and temporal resolution of the reflectometer. After table experiment, we will optimize reflectometry hardware parament such as microwave source calibration to reduce the nonlinear frequency output of the source, reduce the effect of waveguide dispersion through the table experiment calibration, determine the valid angle range between transmitting antenna and plasma cutoff layer, adjust the length of delay line to makes the intermediate frequency falls in the optimal detection range.Based on the characteristics of frequency modulation reflectometer, the thesis us-ing two analytical methods in data processing:time-frequency analysis method and CDM method. The time-frequency analysis do a lot of spectrum analysis to IF data acquisition in a sweep period, then getting IF frequency over time, then calculating the time delay through transmitting frequency, after that the time delay is utilize to get phase delay, at last density profile was acquired according to ordinary mode and extraordinary mode dispersion relation in plasma. In data process, there are some parasitic reflect interference the process of spectral analysis, we used three different peak search algorithms:best path method, the burst-mode method, adaptive spectrum method. Digital complex demodulation (CDM) method move spectrum of IF sig-nal,then filtering them which can directly obtained IF signal phase delay. This two methods utilize at different environment, the CDM can apply in the intermediate fre-quency spectrum with a narrow frequency range, while the time-frequency analysis can be used in a broader frequency spectrum.At last, the thesis describes three experiments of the reflectometer, these are at EAST and J-TEXT respectively. In EAST tokamak single V-band extraordinary wave mode was apply at first time, it has been get part density profile at the first experiment; With the dual-polarized reflectometer at J-TEXT,profile density can cover entire low-field side Plasma density of the tokamak, at the same time the Left hand wave mode microwave was observer at J-TEXT; The second experiment at EAST also used a dual-polarized measurement, while In order to improve signal to noise ratio we will install the antenna inside the vacuum chamber, and a low-loss over mode waveguide was apply as microwave transmission line.