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

Old Dominion University Research Foundation, Norfolk VA

Investigators

Abstract

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.