Gradient Improvement by Removal of Identified Local Defects

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Recent experience of ILC cavity processing and testing at Jefferson Lab has shown that some 9-cell cavities are quench limited at a gradient in the range of 15-25 MV/m. Further studies reveal that these quench limits are often correlated with sub-mm sized and highly localized geometrical defects at or near the equator weld. There are increasing evidence to show that these genetic defects have their origin in the material or in the electron beam welding process (for example due to weld irregularities or splatters on the RF surface and welding porosity underneath the surface). A local defect removal method has ... continued below

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Geng, R. L.; Clemens, W. A.; Cooper, C. A.; Hayano, H. & Watanabe, K. July 2011.

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Recent experience of ILC cavity processing and testing at Jefferson Lab has shown that some 9-cell cavities are quench limited at a gradient in the range of 15-25 MV/m. Further studies reveal that these quench limits are often correlated with sub-mm sized and highly localized geometrical defects at or near the equator weld. There are increasing evidence to show that these genetic defects have their origin in the material or in the electron beam welding process (for example due to weld irregularities or splatters on the RF surface and welding porosity underneath the surface). A local defect removal method has been proposed at Jefferson Lab by locally re-melting the niobium material. Several 1-cell cavities with known local defects have been treated by using the JLab local e-beam re-melting method, resulting in gradient and Q0 improvement. We also sent 9-cell cavities with known gradient limiting local defects to KEK for local grinding and to FNAL for global mechanical polishing. We report on the results of gradient improvements by removal of local defects in these cavities.

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  • SRF 2011, July 25-29, 2011, Chicago, IL

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  • Report No.: JLAB-ACC-11-1457
  • Report No.: DOE/OR/23177-2416
  • Grant Number: AC05-06OR23177
  • Office of Scientific & Technical Information Report Number: 1057776
  • Archival Resource Key: ark:/67531/metadc836107

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  • July 2011

Added to The UNT Digital Library

  • May 19, 2016, 9:45 a.m.

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  • June 2, 2016, 3:36 p.m.

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Geng, R. L.; Clemens, W. A.; Cooper, C. A.; Hayano, H. & Watanabe, K. Gradient Improvement by Removal of Identified Local Defects, article, July 2011; Newport News, Virginia. (digital.library.unt.edu/ark:/67531/metadc836107/: accessed December 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.