Author: Tian, H.
Paper Title Page
MOP030 Analysis of Surface Nitrides Created During "Doping" Heat Treatments of Niobium 106
  • J.K. Spradlin, A.D. Palczewski, C.E. Reece, H. Tian
    JLab, Newport News, Virginia, USA
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The benefits of reduced RF losses from interstitial "doping" of niobium are well established. Many of the details involved in the process remain yet to be elucidated. The niobium surface reacted with low-pressure nitrogen at 800°C presents a surface with chemical reactivity different than standard niobium. While standard "recipes" are being used to produce cavities, we seek additional insight into the chemical processes that may be used to remove the "undesirable" as-formed surface layer. This may lead to new processing routes or quality assurance methods to build confidence that all surface "nitrides" have been removed. We report a series of alternate chemistry treatments and subsequent morphological examinations and interpret the results. We also introduce a new standardized Nb sample system in use for efficient characterization of varying doping protocols and cross-laboratory calibration.
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About • paper received ※ 23 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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HF-Free Bi-Polar Electropolishing for Application on Multi-Cell Elliptical Cavities  
  • H. Tian, M. Lester, J. Musson, H.L. Phillips, C.E. Reece
    JLab, Newport News, Virginia, USA
  • T.D. Hall, M.E. Inman, R. Radhakrishnan, E.J. Taylor
    Faraday Technology, Inc., Clayton, Ohio, USA
  Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC0506OR23177
Pulse reversed electropolishing of niobium SRF cavities, using a dilute aqueous H2SO4 electrolyte without HF yields equivalent RF performance with traditional EP. A pulse reversed electropolishing (BPEP) system has been implemented at Jefferson lab, and applied to single cells, a 7-cell CEBAF C100 cavity, and to 9-cell TESLA-style cavities with upgraded pulse system recently. A systematically mechanistic characterization and understanding of the BPEP process through bench top coupons study and cavities directs a system and operational parameter refinement for BPEP. We present process parameters, removal characterization, and rf performance of the processed cavities. This is the fruit of collaborative work between Jefferson Lab and Faraday Technology, Inc., directed toward the routine commercialization/industrialization of niobium cavity processing.
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