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

Journal Article · 04 December 2015 · AIP Conference Proceedings

DOI: https://doi.org/10.1063/1.4935318 · OSTI ID:1236018

Sung, Zu -Hawn ^[1]; Lee, Peter J.  ^[2]; Polyanskii, Anatolii ^[2]; Balachandran, Shreyas ^[2]; Chetri, Santosh ^[2]; Larbalestier, David C. ^[3]; Wang, Mingmin ^[4]; Compton, Christopher ^[4]; Bieler, Thomas R. ^[4]

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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)

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, bi-crystal and tri-crystal Nb coupons as representative as possible of the surface properties of cavities manufactured by standard techniques.

• Research Organization: Florida State Univ., Tallahassee, FL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP)
• Grant/Contract Number: SC0009960
• OSTI ID: 1236018
• Journal Information: AIP Conference Proceedings, Vol. 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; ISSN 0094-243X
• Publisher: AIPCopyright Statement
• Country of Publication: United States
• Language: English