Development of O-mode/X-mode selected Reflectometry and its application to the Large Helical Device

我们一直在开发微波反射计，用于大型螺旋装置（LHD）上的密度分布和波动测量。由于LHD具有复杂的磁场位形，并且具有大的磁剪切，发射、反射的微波可能具有复杂的行为。为了研究强磁剪切的影响，我们采用了脉冲雷达反射计。由于脉冲雷达反射计测量反射脉冲的延迟时间，因此即使返回意外脉冲，也可以区分X模式和O模式偏振波。本年度，我们研制并应用了新的超短脉冲反射计系统，对LHD等离子体进行了更宽空间范围的测量。实验结果如下：1.我们构建了四通道脉冲雷达反射计系统，每个脉冲宽度约为1ns。当微波的电场方向调整等离子体边缘位置处的磁场方向时，我们可以选择所需的反射波的偏振。得到了等离子体反射脉冲的功率沿着微波极化旋转角的变化规律.采用O模操作，截止层的时间运动和重建的密度分布与FIR干涉仪信号几乎一致.利用X模式操作，发现旋转岛被扭曲的密度涨落局限于极低密度各态历经层.我们研制了一种新的反射计系统，采用了时间宽度为23ps的超短脉冲。在初始实验中，可以测量到截止层被燃料芯块注入到等离子体中所移动。

We have been developing the microwave reflectometer for the density profile and fluctuation measurements on the Large Helical Device (LHD). Since LHD has a complex magnetic field configuration and also has large magnetic shear, the launched, reflected microwave may have complicated behavior. To study the effect of strong magnetic shear, we apply the pulsed radar reflectometer. Because the pulsed radar reflectometry measures the delay time of the reflected pulse, it can be distinguished between X-mode and O-mode polarized waves even if unexpected pulses are returned. In this year we have developed and applied ultra-short-pulse reflectometer system newly to measure wider spatial range of LHD plasma. Experimental results are as follows:1. We constructed four channel pulsed radar reflectometer system which each pulse width is about 1ns. When the direction of the electric field of the microwave adjusts the direction of the magnetic field at the location of the plasma edge, we can select the desired polarization of the reflected wave. It is obtained that the power of the reflected pulse from the plasma changes along the rotating angle of the microwave polarization.2. By using O-mode operation, the temporal motion of the cutoff layer and the reconstructed density profile are almost in agreement with the FIR interferometer signal.3. By using X-mode operation, the density fluctuation that the rotating island is conjectured is found to localize in the very low-density ergodic layer.4. We have developed new reflectometer system using an ultra-short-pulse which temporal width is 23ps. On initial experiment, it can be measured that the cutoff layer is moved by the fuel pellet injection into the plasma.