Mode conversion and high-efficient transmission of submillimeter wave gyrotron output for plasma diagnostics

在福井大学，我们开发了超高频，中等功率，步进可调，亚毫米波回旋加速器（回旋加速器FU系列），在回旋加速器基频和二次谐波共振下工作。陀螺的频率范围可达890 GI-lz，功率水平在100W至1kw之间。在本研究中，我们开发了一种传输线系统来输出我们的亚毫米波陀螺，用于热核聚变装置中自发激发的密度波动的散射测量。(1)我们设计和制造了在156 GHz （TE12腔模式）到812 GHz （TE19腔模式）宽频率范围内工作的传输线组件。即转换为高斯模式的天线系统，由两个带凹槽的金属反射镜组成的偏振片，等等。利用这些元件构建了完整的传输线，并利用回旋加速器FU iv的输出功率进行了测试，观察了等离子体散射点的辐射模式，并以此来确定传输效率。(2)利用回旋管输出功率测试了偏振器的特性。偏振方向可以通过调节两反射镜凹槽之间的相对角度来控制。(3)观测结果与传输线设计参数的预期结果吻合较好，拟将传输线应用于热核聚变装置的亚毫米波散射测量。

In Fukui University, we have developed ultra-high frequency, medium-power, step-tunable, submillimeter wave gyrotrons (Gyrotron FU Series), operating at cyclotron fundamental and second harmonic resonances. The gyrotrons cover the frequency range up to 890 GI-lz and the power levels are between 100W and 1 kW.In this study, we developed a transmission line system to conduct the output of our submillimeter wave gyrotrons for application to scattering measurement of density fluctuations excited spontaneously in thermonuclear fusion devices.(1) We have designed and manufactured components of the transmission line operating in a wide frequency range from 156 GHz (TE12 cavity mode) to 812 GHz (TE19 cavity mode). Namely, an antenna system for conversion to Gaussian mode, polarizer consisting of two metal mirrors with grooves, and so on. The complete transmission line was constructed using these components and tested by using the output power of Gyrotron FU IV.Radiation patterns at the point of scattering in a plasma were observed and the transmission efficiency was determined by the result.(2) The characteristics of the polarizer were tested by using the gyrotron output power. The direction of polarization can be controlled by adjusting the relative angle between grooves of the two mirrors.(3) The observed results are in good agreement with those expected from the design parameters of the transmission line, We have planned to apply the line to submillimeter wave scattering measurements of thermonuclear fusion devices.