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介绍了在HL-2A装置上发展的一套快速扫频的Q波段外差微波反射系统,用于高时空分辨测量等离子体边缘到约束区的电子密度分布。该系统采用外差式连续波扫频调制技术(VCO),由外部任意波电压控制,工作频率为33~50GHz,全波段扫频周期达到6μs。在台面标定中发展了VCO源的动态标定技术,并解决了微波源及器件的非线性响应、波导的色散特性等因素造成差频频率动态范围过大的问题,使反射面固定时系统输出的差频为定频信号,有利于降低噪声干扰和数据处理。同时发展了直接相位处理技术,实现快速的电子密度分布反演。实验中用该微波反射系统测得了L模、H模等不同等离子体放电条件下的电子密度分布,观测ELM爆发前后台基区的形成与垮塌过程。
A rapid swept Q-band heterodyne microwave reflection system developed on the HL-2A device is introduced for the high spatio-temporal resolution of the electron density distribution from the edge to the confinement area of the plasma. The system uses heterodyne continuous wave swept modulation (VCO), which is controlled by external arbitrary voltage. The operating frequency is 33 ~ 50GHz, and the full-band sweep cycle reaches 6μs. In the mesa calibration, the dynamic calibration technology of VCO source is developed, and the nonlinear frequency response of the microwave source and the device, the dispersive characteristics of the waveguide and other factors result in the problem of too much dynamic range of the differential frequency frequency. When the reflective surface is fixed, The difference frequency is a fixed-frequency signal, which helps to reduce noise interference and data processing. At the same time, direct phase processing technology has been developed to achieve rapid electron density distribution inversion. In the experiment, the electron density distribution under different plasma discharge conditions, such as L-mode and H-mode, was measured by the microwave reflection system. The formation and collapse of the basement zone before and after the ELM explosion were observed.