Parajuli I P, Ciovati G, Delayen J R
Center for Accelerator Science, Department of Physics, Old Dominion University, Norfolk, Virginia 23529, USA.
Rev Sci Instrum. 2021 Oct 1;92(10):104705. doi: 10.1063/5.0063177.
Superconducting radio frequency (SRF) cavities are fundamental building blocks of modern particle accelerators. They operate at liquid helium temperatures (2-4 K) to achieve very high quality factors (10-10). Trapping of magnetic flux within the superconductor is a significant contribution to the residual RF losses, which limit the achievable quality factor. Suitable diagnostic tools are in high demand to understand the mechanisms of flux trapping in technical superconductors, and the fundamental components of such diagnostic tools are magnetic field sensors. We have studied the performance of commercially available Hall probes, anisotropic magnetoresistive sensors, and flux-gate magnetometers with respect to their sensitivity and capability to detect localized, low magnetic flux amplitudes, of the order of a few tens of magnetic flux quantum at liquid helium temperatures. Although Hall probes have the lowest magnetic field sensitivity (∼96 nV/μT at 2 K), their physical dimensions are such that they have the ability to detect the lowest number of trapped vortices among the three types of sensors. Hall probes and anisotropic magnetoresistive sensors have been selected to be used in a setup to map regions of trapped flux on the surface of a single-cell SRF cavity.
超导射频（SRF）腔是现代粒子加速器的基本组成部分。它们在液氦温度（2 - 4 K）下运行，以实现非常高的品质因数（10⁵ - 10⁸）。超导体内部磁通的俘获是残余射频损耗的一个重要因素，这限制了可达到的品质因数。为了解技术超导体中磁通俘获的机制，对合适的诊断工具需求很高，而此类诊断工具的基本组件是磁场传感器。我们研究了市售霍尔探头、各向异性磁阻传感器和磁通门磁力计在液氦温度下的灵敏度以及检测局部低磁通幅值（几十磁通量子量级）的能力。尽管霍尔探头的磁场灵敏度最低（2 K时约为96 nV/μT），但其物理尺寸使其能够检测三种类型传感器中俘获涡旋数量最少的情况。已选择霍尔探头和各向异性磁阻传感器用于绘制单单元SRF腔表面磁通俘获区域的装置中。
