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

我们一直在研制用于大螺旋装置（LHD）密度分布和波动测量的微波反射计。由于LHD具有复杂的磁场结构和较大的磁剪切，发射反射的微波可能具有复杂的行为。为了研究强磁切变的影响，我们采用脉冲雷达反射计。由于脉冲雷达反射计测量的是反射脉冲的延迟时间，因此即使返回了意外的脉冲，也可以区分x模式和o模式极化波。在这一年中，我们研制并应用了超短脉冲反射计系统来测量更大空间范围的LHD等离子体。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的磁场方向时，我们可以选择所需的反射波偏振。结果表明，等离子体反射脉冲的功率随微波偏振角的变化而变化。通过o模式运算，截断层的时间运动和重建的密度剖面与FIR干涉仪信号基本吻合。通过x模运算，发现推测的旋转岛的密度波动集中在极低密度遍历层。我们开发了一种使用时间宽度为23ps的超短脉冲的新型反射计系统。在初始实验中，可以测量到由于燃料颗粒注入等离子体中，切断层发生了移动。

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.