Study of Plasma Fluctuation Visualization Using Imaging Reflectometry

在这个研究项目期间，获得了以下结果：1)改进了毫米波二维成像阵列，并将其应用于GAMMA 10串联反射镜上，实现了一次等离子体发射同时测量相位成像和电子回旋发射成像。2)与Teratec公司合作制造了一种使用MMIC技术的新型探测器。该探测器由一个领结天线、一个使用肖特基势垒二极管的下转换混频器和GaAs衬底上的HBT（异质结双极晶体管）放大器组成。在70-140 GHz频段对探测器的外差特性进行了评估。在10 GHz以内的中频响应范围内，比混合探测器的响应范围宽一个数量级。3)采用射线追踪法将辐射信号聚焦到探测器阵列上，设计了国家聚变科学研究所（NIFS）大型螺旋装置（LHD）上的ECE成像光学系统。它由一个椭球镜和面镜组成。点源的艾里方向图和140 GHz的放大系数与设计值吻合较好。4)在LHD中安装毫米波成像系统。同时在两个探测器的IF=1-4 GHz通道上确认ECE信号。将调频和超短脉冲反射器应用于具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带宽为50 GHz的数字化示波器上，并通过基于小波变换的相位提取方法和依赖于行信号波形而不是依赖于作为频率函数的群延迟的层析方法进行分析。结果表明，该系统具有时间分辨等离子体密度剖面测量和低温处理等离子体测量的潜力。

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.