Annealing to Mitigate Pitting in Electropolished Niobium Coupons and SRF Cavities

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Ongoing studies at Fermilab investigate whether dislocations and other factors instigate pitting during cavity electropolishing (EP), despite careful processing controls and the inherent leveling mechanism of EP itself. Here, cold-worked niobium coupons, which exhibited increased tendencies for pitting in our past study, were annealed in a high vacuum furnace and subsequently processed by EP. Laser confocal scanning microscopy and special defect counting algorithms were used to assess the population of pits formed. Hardness measurements indicated that annealing for 2 hours at 800 C produced recovery, whereas annealing for 12 hours at 600 C did not, as is consistent with known ... continued below

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8 pages

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Cooley, L.D.; Hahn, E.; Hicks, D.; Romanenko, A.; Schuessler, R.; Thompson, C. et al. June 8, 2011.

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Ongoing studies at Fermilab investigate whether dislocations and other factors instigate pitting during cavity electropolishing (EP), despite careful processing controls and the inherent leveling mechanism of EP itself. Here, cold-worked niobium coupons, which exhibited increased tendencies for pitting in our past study, were annealed in a high vacuum furnace and subsequently processed by EP. Laser confocal scanning microscopy and special defect counting algorithms were used to assess the population of pits formed. Hardness measurements indicated that annealing for 2 hours at 800 C produced recovery, whereas annealing for 12 hours at 600 C did not, as is consistent with known changes for cavities annealed in a similar way. The 800 C anneal was effective in some cases but not others, and we discuss reasons why tendencies for pitting remain. We discuss implications for cavities and continued work to understand pitting.

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8 pages

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  • Presented at Cryogenic Engineering Conference and International Cryogenic Materials Conference CEC-ICMC 2011, Spokane, Washington, 13-17 June 2011

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  • Report No.: FERMILAB-CONF-11-264-TD
  • Grant Number: AC02-07CH11359
  • Office of Scientific & Technical Information Report Number: 1021486
  • Archival Resource Key: ark:/67531/metadc830516

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  • June 8, 2011

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  • May 19, 2016, 3:16 p.m.

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  • Aug. 25, 2016, 2:57 p.m.

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Cooley, L.D.; Hahn, E.; Hicks, D.; Romanenko, A.; Schuessler, R.; Thompson, C. et al. Annealing to Mitigate Pitting in Electropolished Niobium Coupons and SRF Cavities, article, June 8, 2011; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc830516/: accessed April 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.