{"data":{"abstract":{"value":"
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. The local magnetic field enhancement produced by the sharp-edge features observed on the samples is not sufficient to explain the observed degradation of the cavity quality factor, which starts at peak surface magnetic field as low as 20 mT.
","format":"html"},"articleType":"article","authors":[{"type":"Person","name":"Xin Zhao","firstname":"Xin","surname":"Zhao","affiliationIds":["a1"]},{"type":"Person","name":"G. Ciovati","firstname":"G.","surname":"Ciovati","affiliationIds":["a1"]},{"type":"Person","name":"T. R. Bieler","firstname":"T. R.","surname":"Bieler","affiliationIds":["a2"]}],"affiliations":[{"name":"Thomas Jefferson National Accelerator Facility (Jefferson Lab), 12000 Jefferson Avenue, Newport News, Virginia 23606, USA","id":"a1"},{"name":"Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824, USA","id":"a2"}],"notes":[{"format":"html","value":"Corresponding author.
\ngciovati@jlab.org
","label":"*","id":"n1","type":"contrib"}],"date":"2010-12-15","type":"article","metadata_last_modified_at":"2010-12-15T16:08:25+0000","last_modified_at":"2014-08-22T04:12:59+0000","id":"10.1103/PhysRevSTAB.13.124701","identifiers":{"doi":"10.1103/PhysRevSTAB.13.124701"},"issue":{"number":"12"},"pageStart":"124701","hasArticleId":true,"numPages":11,"publisher":{"name":"APS"},"rights":{"rightsStatement":"© 2010 The American Physical Society","copyrightYear":2010,"copyrightHolders":[{"name":"The American Physical Society"}],"creativeCommons":true,"licenses":[{"url":"http://creativecommons.org/licenses/by/3.0/","licenseStatement":"This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI."}]},"journal":{"id":"PRSTAB","abbreviatedName":"Phys. Rev. ST Accel. Beams","name":"Physical Review Special Topics - Accelerators and Beams"},"title":{"value":"Characterization of etch pits found on a large-grain bulk niobium superconducting radio-frequency resonant cavity","format":"html"},"tocSection":{"label":"Applications"},"volume":{"number":"13"}}}