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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. In addition, 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 cut-out single,more » bi-crystal and tri-crystal Nb coupons as representative as possible of the surface properties of cavities manufactured by standard techniques.« less
Authors:
 [1] ;  [2] ;  [2] ;  [2] ;  [2] ;  [3] ;  [4] ;  [4] ;  [4]
  1. US-Steel, Pittsburgh, PA (United States); Florida State Univ., Tallahassee, FL (United States)
  2. Florida State Univ., Tallahassee, FL (United States)
  3. Florida State Univ., Tallahassee, FL (United States); Florida A & M Univ., Tallahassee, FL (United States)
  4. Michigan State Univ., East Lansing, MI (United States)
Publication Date:
OSTI Identifier:
1236018
Grant/Contract Number:
SC0009960
Type:
Accepted Manuscript
Journal Name:
AIP Conference Proceedings
Additional Journal Information:
Journal Volume: 1687; Conference: Science And Technology Of Ingot Niobium For Superconducting Radio Frequency Applications, Jefferson Lab, VA (United States), 4 Dec 2015; Related Information: ISBN 978-0-7354-1334-4; Journal ID: ISSN 0094-243X
Publisher:
AIP
Research Org:
Florida State Univ., Tallahassee, FL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE SRF cavities; Nb; magneto optical; niobium; grain boundaries; magnetooptical effects; microstructural properties; superconductivity