Ikezoe R, Ichimura M, Okada T, Itagaki J, Hirata M, Sumida S, Jang S, Izumi K, Tanaka A, Yoshikawa M, Kohagura J, Sakamoto M, Nakashima Y
Plasma Research Center, University of Tsukuba, Tsukuba 305-8577, Japan.
Rev Sci Instrum. 2017 Mar;88(3):033504. doi: 10.1063/1.4978323.
A two-channel microwave reflectometer system with fast microwave antenna switching capability was developed and applied to the GAMMA 10 tandem mirror device to study high-frequency small-amplitude fluctuations in a hot mirror plasma. The fast switching of the antennas is controlled using PIN diode switches, which offers the significant advantage of reducing the number of high-cost microwave components and digitizers with high bandwidths and large memory that are required to measure the spatiotemporal behavior of the high-frequency fluctuations. The use of two channels rather than one adds the important function of a simultaneous two-point measurement in either the radial direction or the direction of the antenna array to measure the phase profile of the fluctuations along with the normal amplitude profile. The density fluctuations measured using this system clearly showed the high-frequency coherent fluctuations that are associated with Alfvén-ion-cyclotron (AIC) waves in GAMMA 10. A correlation analysis applied to simultaneously measured density fluctuations showed that the phase component that was included in a reflected microwave provided both high coherence and a clear phase difference for the AIC waves, while the amplitude component showed neither significant coherence nor clear phase difference. The axial phase differences of the AIC waves measured inside the hot plasma confirmed the formation of a standing wave structure. The axial variation of the radial profiles was evaluated and a clear difference was found among the AIC waves for the first time, which would be a key to clarify the unknown boundary conditions of the AIC waves.
开发了一种具有快速微波天线切换能力的双通道微波反射计系统，并将其应用于GAMMA 10串联镜装置，以研究热镜等离子体中的高频小振幅波动。天线的快速切换由PIN二极管开关控制，这具有显著优势，即减少了测量高频波动时空行为所需的高成本微波组件以及具有高带宽和大内存的数字化仪的数量。使用两个通道而非一个通道增加了在径向或天线阵列方向上进行同步两点测量的重要功能，以便在测量波动的正常幅度分布的同时测量波动的相位分布。使用该系统测量的密度波动清楚地显示了与GAMMA 10中的阿尔文离子回旋波（AIC波）相关的高频相干波动。对同时测量的密度波动进行的相关性分析表明，反射微波中包含的相位分量为AIC波提供了高相干性和明显的相位差，而幅度分量既没有显著的相干性也没有明显的相位差。在热等离子体内部测量的AIC波的轴向相位差证实了驻波结构的形成。首次评估了径向分布的轴向变化，并发现AIC波之间存在明显差异，这将是阐明AIC波未知边界条件的关键。
