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Title: Characterization of etch pits found on a large-grain bulk niobium superconducting radio-frequency resonant cavity

The performance of superconducting radio-frequency (SRF) resonant cavities made of bulk niobium is limited by nonlinear localized effects. Surface analysis of regions of higher power dissipation is thus of intense interest. Such areas (referred to as “hotspots”) were identified in a large-grain single-cell cavity that had been buffered-chemical polished and dissected for examination by high resolution electron microscopy, electron backscattered diffraction microscopy (EBSD), and optical microscopy. Pits with clearly discernible crystal facets were observed in both “hotspot” and “coldspot” specimens. The pits were found in-grain, at bicrystal boundaries, and on tricrystal junctions. They are interpreted as etch pits induced by crystal defects (e.g. dislocations). All coldspots examined had a qualitatively lower density of etch pits or relatively smooth tricrystal boundary junctions. EBSD mapping revealed the crystal orientation surrounding the pits. Locations with high pit density are correlated with higher mean values of the local average misorientation angle distributions, indicating a higher geometrically necessary dislocation content. In addition, a survey of the samples by energy dispersive x-ray analysis did not show any significant contamination of the samples’ surface. In conclusion, the local magnetic field enhancement produced by the sharp-edge features observed on the samples is not sufficient to explain the observedmore » degradation of the cavity quality factor, which starts at peak surface magnetic field as low as 20 mT.« less
Authors:
 [1] ;  [1] ;  [2]
  1. Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
  2. Michigan State Univ., East Lansing, MI (United States)
Publication Date:
OSTI Identifier:
1001033
Report Number(s):
JLAB-ACC--09-1123; DOE/OR/23177--1066
Journal ID: ISSN 1098-4402; PRABFM; TRN: US201101%%799
Grant/Contract Number:
AC05-06OR23177
Type:
Accepted Manuscript
Journal Name:
Physical Review Special Topics. Accelerators and Beams
Additional Journal Information:
Journal Volume: 13; Journal Issue: 12; Journal ID: ISSN 1098-4402
Publisher:
American Physical Society (APS)
Research Org:
Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; BICRYSTALS; CAVITIES; CONTAMINATION; CRYSTAL DEFECTS; DIFFRACTION; DISLOCATIONS; ELECTRON MICROSCOPY; ELECTRONS; MAGNETIC FIELDS; MICROSCOPY; NIOBIUM; OPTICAL MICROSCOPY; ORIENTATION; PERFORMANCE; QUALITY FACTOR; RESOLUTION