Analysis of Magnetic Vortex Dissipation in Sn-Segregated Boundaries in Nb${}_3$Sn Superconducting RF Cavities

Abstract

We study mechanisms of vortex nucleation in Nb${}_3$Sn Superconducting RF (SRF) cavities using a combination of experimental, theoretical, and computational methods. Scanning transmission electron microscopy (STEM) image and energy dispersive spectroscopy (EDS) of some Nb${}_3$Sn cavities show Sn segregation at grain boundaries in Nb${}_3$Sn with Sn concentration as high as $\sim$35 at.\% and widths $\sim$3 nm in chemical composition. Using ab initio calculations, we estimate the effect excess tin has on the local superconducting properties of the material. We model Sn segregation as a lowering of the local critical temperature. We then use time-dependent Ginzburg-Landau theory to understand the role of segregation on magnetic vortex nucleation. Our simulations indicate that the grain boundaries act as both nucleation sites for vortex penetration and pinning sites for vortices after nucleation. Depending on the magnitude of the applied field, vortices may remain pinned in the grain boundary or penetrate the grain itself. We estimate the superconducting losses due to vortices filling grain boundaries and compare with observed performance degradation with higher magnetic fields. We estimate that the quality factor may decrease by an order of magnitude ($10^{10}$ to $10^9$) at typical operating fields if 0.03\% of the grain boundaries actively nucleate vortices. We additionally estimate the volume that would need to be filled with vortices to match experimental observations of cavity heating.

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Cited by in corpus (8)

• $\text{Ab Initio}$ Study of Antisite Defects in Nb${}_3$Sn: Phase Diagram and Impact on Superconductivity
• Impact of border defects on the magnetic flux penetration in superconducting films
• Microscopic Examination of SRF-quality Nb Films through Local Nonlinear Microwave Response
• Microwave Microscope Studies of Trapped Vortex Dynamics in Superconductors
• A Time-Dependent Ginzburg-Landau Framework for Sample-Specific Simulation of Superconductors for SRF Applications
• Microscopic Investigation of rf Vortex Nucleation in Nb3Sn Films Using a Near-Field Magnetic Microwave Microscope
• Dissipation by surface states in superconducting RF cavities
• Electropolishing-Induced Topographic Defects in Niobium: Insights and Implications for Superconducting Radio Frequency Applications