Magnetic Field Mapping of Vortex Hotspots and Identifying the Sources of Losses in Superconducting Accelerating Cavities

许多物理学领域的研究都依赖于使用加速器来产生高能粒子束，这些粒子束可用于从基础研究到医学治疗再到材料加工的广泛活动。 大多数加速器的设计依赖于移动粒子通过一系列磁共振腔，类似于微波炉，为光束提供能量。 今天，通过使用超导磁体向腔体提供能量，可以通过加速器达到非常高的能量。 但是对于任何空腔，梁的行为都受到空腔内磁场结构的强烈影响。 这项工作的目的是通过解决腔体内磁场不规则性的影响来提高现代粒子加速器中使用的超导谐振腔的性能和效率。一个新的实验装置将开发沿着与新的理论模型进行这项研究。这项研究将为培养粒子加速器和固态物理领域的一名本科生和两名研究生提供机会，并将提供新的方法来降低基础科学和应用科学中使用的粒子加速器的运营成本。该项目将研究超导射频（RF）铌腔中涡旋在不同条件下的捕获和耗散机制，例如冷却速率，表面处理和剩余磁场。将开发一种新型的温度和磁扫描组合系统，以检测和量化捕获的磁通量及其对腔RF损耗的影响。实验工作将集成的涡流分布的数值重建和理论研究的捕获涡束在腔体的冷却过程中，通过临界温度，以及在高RF磁场振幅的表面电阻的涡流的贡献。

Research in a number of areas of physics relies on the use of accelerators to generate beams of particles moving at high energy that are used in a broad spectrum of activities, from fundamental research to medical treatments to materials processing. Most accelerator designs rely on moving the particles through a series of magnetic resonant cavities, similar to a microwave oven, to supply energy to the beam. The very high energies that can be reached through accelerators today has been enabled by the use of superconducting magnets to supply the energy to the cavity. But with any cavity, the behavior of the beam is strongly influenced by the structure of the magnetic field within the cavity. This work aims at improving the performance and efficiency of superconducting resonator cavities used in modern particle accelerators by addressing the impact of irregularities in the magnetic field within the cavity. A novel experimental apparatus will be developed along with new theoretical models to carry out this study. This research will provide an opportunity to train one undergraduate and two graduate students in the field of particle accelerators and solid-state physics and will provide new methods to reduce the cost of operation of particle accelerators used in basic and applied sciences. The project will investigate the mechanisms of trapping and dissipation of vortices in superconducting radio-frequency (RF) niobium cavities under different conditions, such as cool-down rates, surface treatments and residual magnetic field. A novel combined temperature and magnetic scanning system will be developed to detect and quantify the amount of trapped flux and its impact on cavity RF losses. The experimental work will be integrated with numerical reconstructions of the vortex distribution and theoretical investigations of trapping of vortex bundles during the cool-down of the cavity through the critical temperature, and the contribution of vortices to the surface resistance at high RF magnetic field amplitudes.