Study of Plasma Fluctuation Visualization Using Imaging Reflectometry

在本研究期间，取得了以下成果：1)改进了毫米波二维成像阵列，并将其应用于伽马10串列镜，实现了在一个等离子体束中同时测量位相成像和电子回旋发射成像。2)与Teratec公司合作制造了一种新型的基于MMIC技术的探测器。该探测器由一个蝴蝶结天线、一个使用肖特基势垒二极管的下变频混频器和一个在砷化镓衬底上的HBT(异质结双极晶体管)放大器组成。在70-140 GHz范围内对探测器的外差特性进行了评估。3)设计了美国国家核聚变科学研究所(National Institute for Fusion Science，NIFS)用于大型螺旋器件(LHD)的光学成像光学系统，采用光线追踪法将辐射信号聚焦到探测器阵列上。它由椭球镜和平面镜组成。4)在LHD上安装了毫米波成像系统，在两个探测器的IF=1-4 GHz通道上同时确认了ECES信号。5)将调频和超短脉冲反射器应用于带有射频源的电感耦合等离子体。在后一种情况下，将反射波直接记录到50 GHz带宽的数字化范围内，并利用基于小波变换的相位提取方法和层析方法进行分析，所述方法依赖于行信号波形而不是作为频率函数的群延迟。结果表明，该系统具有测量LHD等离子体和低温加工等离子体的时间分辨密度分布的潜力。

During the period of this research project, following results were obtained.1) Millimeter-wave two-dimensional imaging array has been improved, and applied to the GAMMA 10 tandem mirror for the simultaneous measurement of phase imaging and ECE (electron cyclotron emission) imaging in one plasma shot.2) A novel detector using MMIC technology has been fabricated in collaboration with Teratec Corporation. The detector consists of the integration of a bow-tie antenna, a down-converting mixer using a Schottky barrier diode, and HBT (hetero-junction bipolar transistor) amplifiers on a GaAs substrate. The heterodyne characteristics of the detector were evaluated at 70-140 GHz. The response of intermediate frequency (IF) up to 10 GHz was confirmed, which is one order broader than that of a hybrid detector.3) The optics for ECE imaging on Large Helical Device (LHD) at the National Institute for Fusion Science (NIFS) were designed by using a ray-tracing method to focus radiation signals onto a detector array. It consists of an ellipsoidal mirror and a plane mirror. The Airy pattern of a point source and the magnification factor at 140 GHz were in good agreement with the designed values.4) The millimeter-wave imaging system was installed in LHD.The ECE signal was confirmed at IF=1-4 GHz channels of two detectors, simultaneously.5) An FM and an ultrashort-pulse reflectomer have been applied to an inductively coupled plasma with a radio frequency source. In the latter case, the reflected waves are directly recorded to a digitizing scope with 50 GHz bandwidth, and analyzed by a wavelet transform based phase extraction method and a tomographic method which rely on a row signal waveform rather than on the group delay as a function of frequency. The results demonstrate the potential of the current system for time resolved density profile measurements of LHD plasmas as well as low temperature processing plasmas.