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Title: Large grain CBMM Nb ingot slices: An ideal test bed for exploring the microstructure-electromagnetic property relationships relevant to SRF

High purity (RRR > 200), large grain (> 5-10 cm) niobium ingot slices have been successfully used to fabricate radio frequency (RF) cavities for particle accelerators. They offer significantly reduced fabrication cost by eliminating processing steps and furthermore they provide the opportunity to study the influence of individual grain boundaries in SRF Nb. Here we summarize our measurements of grain boundary (GB) effects on the superconducting properties of large grain high purity niobium sheet manufactured by CBMM. We show by magneto-optical (MO) imaging that GBs allow premature flux penetration, but only when they are oriented close to the direction of the magnetic field. However, even low angle GBs produced by minor deformations commensurate with half-cell forming produce localized flux penetration. The transport properties of grain boundaries were investigated by direct transport across them and evidence for preferential vortex flow along the GBs of SRF Nb was observed for the first time. Using transmission electron microscopy (TEM) and micro crystallographic analysis with electron backscattered diffraction (EBSD), we were able to quantitatively characterize surface substructures that can lead to localized thermal breakdown of superconductivity. Important to these studies was the development of sample preparation techniques that made the cutout single, bi-crystal and tri-crystalmore » Nb coupons as representative as possible of the surface properties of cavities manufactured by standard techniques.« less
Authors:
 [1] ;  [2] ; ; ; ;  [1] ;  [1] ;  [2] ; ; ;  [3]
  1. The Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee FL 32310, US (United States)
  2. (United States)
  3. Michigan State University, US (United States)
Publication Date:
OSTI Identifier:
22492685
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1687; Journal Issue: 1; Conference: Ingot niobium summary workshop, Newport News, VA (United States), 4 Dec 2015; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ACCELERATORS; BACKSCATTERING; CAVITIES; CRYSTALLOGRAPHY; CRYSTALS; ELECTRON DIFFRACTION; FABRICATION; GRAIN BOUNDARIES; IMAGES; MAGNETIC FIELDS; NIOBIUM; RADIOWAVE RADIATION; RF SYSTEMS; SAMPLE PREPARATION; SUPERCONDUCTING CAVITY RESONATORS; SUPERCONDUCTIVITY; SURFACE PROPERTIES; TRANSMISSION ELECTRON MICROSCOPY; VORTEX FLOW