The Advanced Photon Source plans to upgrade to a multibend achromat (MBA) lattice that will dramatically decrease the electron beam emittance, thereby enhancing the x-ray brightness by two to three orders of magnitude. Electron beam focusing in the MBA requires small-aperture vacuum components that must also have a small impedance so as to minimize rf-heating and collective instabilities. As part of this effort, this paper focuses on coupling impedance measurements and analysis of certain critical Advanced Photon Source Upgrade vacuum components. Impedance measurements of accelerator components have traditionally been done with the coaxial wire method, which is based on the fact that the Transverse Electro-Magnetic (TEM) mode of the coaxial cable can mimic the Coulomb field of a particle beam; however this measurement technique has various limitations. This paper describes our approach to measure the coupling impedance using a Goubau line (G-line), which is essentially a single wire transmission line designed to propagate Sommerfeld-like surface waves whose fundamental Transverse Magnetic (TM) mode mimics the Coulomb field of a relativistic particle beam. We describe in detail the measurement procedure that we have developed for the G-line, including the measurement setup and proper definition of a reference, measurement procedure and advantages, and our experience regarding how to reduce systematic experimental error that we learned over the course of the measurements. Starting with our initial suite of measurements and simulations designed to benchmark and validate the novel G-line based measurement technique, we present the measured results for several Advanced Photon Source Upgrade vacuum components, including those of two rf-gasket designs and the beam position monitor-bellows assembly.

中文翻译：

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测量Argonne高级光子源升级的真空组件阻抗

Advanced Photon Source计划升级到多弯消色差（MBA）晶格，该晶格将大大降低电子束发射率，从而将X射线亮度提高2到3个数量级。MBA中的电子束聚焦需要小孔径的真空组件，这些组件还必须具有小的阻抗，以最大程度地减小射频加热和集体不稳定性。作为这项工作的一部分，本文重点介绍耦合阻抗测量和某些关键的高级光子源升级真空组件的分析。传统上，加速器组件的阻抗测量是使用同轴线方法完成的，该方法基于以下事实：同轴电缆的横向电磁（TEM）模式可以模仿粒子束的库仑场；然而，这种测量技术具有多种局限性。本文介绍了我们使用Goubau线（G线）测量耦合阻抗的方法，该线本质上是一条单线传输线，旨在传播类似于Sommerfeld的表面波，其基本横向磁（TM）模式模仿了A的库仑场。相对论粒子束。我们将详细介绍我们为G线开发的测量程序，包括测量设​​置和参考的正确定义，测量程序和优势，以及我们在减少过程中学到的如何减少系统实验误差的经验。测量。从我们最初用于衡量和验证基于G线的新颖测量技术的初始测量和仿真套件开始，