Upgrade Of The Microwave Reflectometry System On J-TEXT Tokamak

The work of this paper mainly focuses on the upgrade of the microwave diagnostic reflection system on the J-TEXT tokamak.It includes two aspects:The microwave reflectometry for density profile measurement was optimized and improved from both hardware and software.A sweep doppler reflectometry for measuring plasma polar rotation,density disturbance,radial electric field and other parameters has been developed.The new reflectometry for density profile measurement consists of three channels:the Q-band（33⁵0 GHz）ordinary mode（O-mode）and the extra-ordinary mode（X-mode）,and the V-band（50⁷5 GHz）X-mode.Under J-TEXT conventional discharge conditions(magnetic field B_T=1.8T,density of center plasma ne=3x10¹⁹m^-3),This reflectometry’s measurable range covers the boundary and center of the low field plasma.In addition,the device’s scan period is 20?s,and 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.In this paper,based on the static calibration of the original voltage-controlled oscillator（VCO）,the dynamically calibrated of VCO is completed,the influence of waveguide dispersion is corrected,and the influence of the circumferential non-uniformity of the vertical field is analyzed.Secondly,This system uses the single sideband modulation,and I/Q phase discrimination is adopted to improve the signal quality.Thirdly the design and writing of the data processing program are completed:the influence of different filtering methods on the phase is analyzed and the frequency sampling method of Linear Phase Filtering（FIR）is used to filter the noise of acquired signal considering the sensitivity of the reflectometry to the phase.Then the numerical algorithm developed by Bottollier has been introduced.This paper uses this method to calculate the density distribution iteratively and the oscillation caused by the iterative error accumulation has been reduced effectively.A sweep doppler reflectometry has been developed.This system works in the U-band（40⁶0GHz）.Heterodyne method is adopted in the hardware.The output frequency of the microwave source is 20³0GHz.It is modulated by a single sideband and then doubled to reach the U-band and then output.The minimum dwell time of each frequency point is2ms,the minimum stabilization time of different frequency points is 1ms,the length of frequency step and the number of steps are adjustable.Three methods for extracting doppler shift are implemented:direct phase differential method,weighted average method and single Gaussian fitting method,and their calculation results are compared.The experiment finds that the direct phase differential method on this system is more accuracy.Finally,microwave reflectometry and doppler reflectometry were used for J-TEXT physics experiments.The microwave reflectometry measured the change in the density profile during the stage of density climbing and achieved good agreement with the results of the polarimetry.And the three-dimensional evolution process of density profile with time is given.The doppler reflectometry observed the change of density perturbation during the SMBI injecting of hydrogen,the density disturbance decreased after injection of gas in the boundary part（r=0.23m）.These results show that the observation data of the two systems can effectively assist the physical experiment.