Flux pinning characteristics in cylindrical ingot niobium used in superconducting radio frequency cavity fabrication

Abstract

We present the results of from DC magnetization and penetration depth measurements of cylindrical bulk large-grain (LG) and fine-grain (FG) niobium samples used for the fabrication of superconducting radio frequency (SRF) cavities. The surface treatment consisted of electropolishing and low temperature baking as they are typically applied to SRF cavities. The magnetization data were fitted using a modified critical state model. The critical current density Jc and pinning force Fp are calculated from the magnetization data and their temperature dependence and field dependence are presented. The LG samples have lower critical current density and pinning force density compared to FG samples which implies a lower flux trapping efficiency. This effect may explain the lower values of residual resistance often observed in LG cavities than FG cavities.

References in corpus (3)

• The Flux-Line Lattice in Superconductors
• Dynamics of vortex penetration, jumpwise instabilities and nonlinear surface resistance of type-II superconductors in strong rf fields
• Surface Superconductivity in Niobium for Superconducting RF Cavities

Cited by in corpus (6)

• Efficient expulsion of magnetic flux in superconducting RF cavities for high $Q_0$ applications
• Flux expulsion in niobium superconducting radio-frequency cavities of different purity and essential contributions to the flux sensitivity
• Field of first flux entry and pinning strength of superconductors for RF application measured with muon spin rotation
• Impact of geometry on the magnetic flux trapping of superconducting accelerating cavities
• Vortex Dynamics and Dissipation Under High-amplitude Microwave Drive
• Measurements of the first-flux-penetration field in surface-treated and coated Nb: Distinguishing between surface pinning and an interface energy barrier