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等离子体中电子密度分布是研究等离子体物理的基础诊断之一.为了测量J-TEXT中电子密度分布,我们在J-TEXT实验装置上搭建了一套频率调制反射计.该反射计工作在Q波段与V波段,为了增加反射计密度测量范围,采用了双极化的设计,即能够同时测量寻常波模式与非寻常波模式.得益于双极化的设计,该反射计测量的电子密度范围为0—6.0×1019m-3,能够覆盖J-TEXT托卡马克的低场侧全部范围.频率调制反射计的时间分辨取决于微波系统扫描周期,由于采用了扫频速率更快的扫频固态源,整个频率扫描周期可以达到40μs.要获得完整的电子密度分布,必须先利用中频频率的跳变计算出密度零点的位置,然后使用两种极化模式的数据反演得到完整的电子密度剖面.同时,在实验中还观察到在非寻常波模式下低于右旋截止频率的微波在等离子体中也能够传播.
In order to measure the electron density distribution in J-TEXT, we set up a set of frequency-modulation reflectometer on J-TEXT experimental device.The work of this reflectometer works in Q Band and V-band, in order to increase the reflectometer density measurement range, the use of dual-polarization design, which can measure both common mode and unusual wave mode.Benefit from the dual polarization design, the reflectometer to measure the electron density The range of 0-6.0 × 1019m-3 covers the entire low-field side of the J-TEXT tokamak.The time resolution of a frequency-modulated reflectometer depends on the scanning period of the microwave system. Due to the swept frequency Solid state source, the entire frequency scanning cycle can be up to 40μs. To obtain a complete distribution of electron density, you must first use the IF frequency hopping to calculate the position of the zero density, and then use the two polarization mode data inversion to obtain the complete electron density Section.At the same time, it is also observed experimentally that microwaves below the right-handed cutoff frequency in the extraordinary wave mode can also propagate in the plasma.