双极化频率调制微波反射计在J-TEXT托卡马克上的应用

Application of dual-polarization frequency-modulated microwave reflectometer to J-TEXT tokamak

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.

A dual-polarization frequency-modulated continuous-wave （FMCW） reflectometer is established on J-TEXT for measuring density profile. The frequency of reflectometer covers both Q band and V band. In order to measure wider density range, ordinary mode polarization and extraordinary mode polarization are utilized at the same time. For the FMCW reflectometer, temporal resolution depends on sweeping rate of the microwave source. Benefited from HTO （hyperabrupt varactortuned oscillator） source, a full frequency sweep period of the reflectometer could be less than 40 μs. Electron density profile from 0-6.0 × 10^19 m-3 can be detected, which covers the whole low field side in J-TEXT. To reconstruct the full density profile, the position of the zero density should be confirmed first, which is determined from where the intermediate frequencies change transiently. Meanwhile, we observe the propagation of left-hand extraordinary wave from data in X-mode reflectometer.