标题： 用于麦迪逊 AWAKE 原型等离子体密度测量的创新外差微波干涉仪 显示英文标题

标题： An Innovative Heterodyne Microwave Interferometer for Plasma Density Measurements on the Madison AWAKE Prototype

摘要： 麦迪逊AWAKE原型（MAP）是一个高功率、高密度的螺旋波等离子体实验。 该项目的主要目标是开发一种可扩展的等离子体源，用于AWAKE项目中的束流驱动等离子体尾场加速器。 我们使用一种新型的外差微波干涉仪来测量等离子体密度，该干涉仪相比传统方法具有多项改进。 设计中使用单一微波源结合上变频器以避免频率漂移并降低整体成本。 椭圆镜将探测光束聚焦到等离子体中并将其引导回接收器。 发射器和接收器以及测量电子设备都位于一个小型外壳内，并由MAP另一侧的两个小镜子协助。 系统的两部分在计算机控制的运动平台上独立移动。 这种设置使得即使有磁铁、布线和结构支撑物会阻碍波导系统移动，也能快速重新定位干涉仪以在任何轴向位置进行测量。 高速、高精度的混合信号电路和FPGA直接在壳体内分析探测信号，从而无需数字转换器或示波器。 干涉仪可以分辨到一个条纹的百分之一的相位变化，从而得到线平均分辨率为$1.5\mathrm{\cdot 10^{17}\; m^{-3}}$。 该系统每$5\;\mathrm{\mu s}$实时测量一次，进入中等$\mathrm{10^{19}\; m^{-3}}$密度范围，噪声水平为$1.0\mathrm{\cdot 10^{17}\; m^{-3}}$。 显示英文摘要

摘要： The Madison AWAKE Prototype (MAP) is a high-power, high-density helicon plasma experiment. The project's main goal is to develop a scalable plasma source for use in a beam-driven plasma wakefield accelerator as part of the AWAKE project. We measure the plasma density with a new heterodyne microwave interferometer that features several improvements over traditional approaches. The design uses a single microwave source combined with an upconverter to avoid frequency drift and reduce overall cost. Elliptical mirrors focus the probe beam into the plasma and guide it back to the receiver. The transmitter and receiver along with the measurement electronics are co-located in a small enclosure and are assisted by two small mirrors on the opposite side of MAP. Both halves of the system move independently on computer-controlled motion platforms. This setup enables fast repositioning of the interferometer to measure at any axial location despite the magnets, wiring and structural supports that would block movement of a waveguide-based system. A high-speed, high-precision mixed signal circuit and FPGA analyze the probe signal directly in the enclosure which obviates the need for a digitizer or oscilloscope. The interferometer resolves phase shifts down to one hundredth of a fringe, resulting in a line-averaged resolution of $1.5\mathrm{\cdot 10^{17}\; m^{-3}}$. The system provides a real-time measurement every $5\;\mathrm{\mu s}$ up into the mid $\mathrm{10^{19}\; m^{-3}}$ density range with a noise level of $1.0\mathrm{\cdot 10^{17}\; m^{-3}}$.