Author: Reece, C.E.
Paper Title Page
WEPRI062 The Joint High Q0 R&D Program for LCLS-II 2627
 
  • M. Liepe, R.G. Eichhorn, F. Furuta, G.M. Ge, D. Gonnella, G.H. Hoffstaetter
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • A.C. Crawford, A. Grassellino, A. Hocker, O.S. Melnychuk, A. Romanenko, A.M. Rowe, D.A. Sergatskov
    Fermilab, Batavia, Illinois, USA
  • R.L. Geng, A.D. Palczewski, C.E. Reece
    JLab, Newport News, Virginia, USA
  • M.C. Ross
    SLAC, Menlo Park, California, USA
 
  The superconducting RF linac for LCLS-II calls for 1.3 GHz 9-cell cavities with an average intrinsic quality factor Q0 of 2.7·1010 at 2K and 16 MV/m accelerating gradient. A collaborative effort between Cornell University, FNAL, and JLab has been set up with the goal of developing and demonstrating a cavity treatment protocol for the LCLS-II cavities meeting these specifications. The high Q0 treatment protocol is based on nitrogen doping of the RF surface layer during a high temperature heat treatment. This novel SRF cavity preparation was recently developed at FNAL and shown to result in SRF cavities of very high Q0 at 2K with an increase in Q0 from low to medium fields. N-doped single cell cavities at Cornell, FNAL, and JLab routinely exceed LCLS-II specification. 9-cell N-doped cavities at FNAL achieve an average Q0(T=2K, 16 MV/m) of ≈ 3.4·1010 with an average quench field of ≈ 19 MV/m, meeting therefore overall with good margin the LCLS-II specification.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI062  
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THOBB01 Pursuing the Origin and Remediation of Low Q0 observed in the Original CEBAF Cryomodules 2828
 
  • R.L. Geng, J.F. Fischer, C.E. Reece, A.V. Reilly
    JLab, Newport News, Virginia, USA
  • F.S. He, Y.M. Li
    PKU, Beijing, People's Republic of China
 
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
We report on results of a new investigation into the Q0 degradation phenomenon observed in original CEBAF cavities when assembled into cryomodules. As a result, the RF dissipation losses increased by roughly a factor of two. The origin of the degradation, first observed in 1994, has remained unresolved up to current period, despite much effort. Recently, a new investigation has been launched, taking advantage of the latest cryomodule to undergo refurbishment. Systematic measurements are conducted with respect to the magnetic shielding effects of the double-layer shields and the magnetic properties of various components within the inner shield. This resulted in the new discovery of strongly magnetized strut springs as a major source of remnant magnetic flux near a cavity inside of all magnetic shielding. New springs with superior magnetic properties have been found, evaluated and implemented into the current cryomodule. In this contribution, we will review the data accumulated so far. Options for complete Q0 preservation of assembled cavities and possible Q0 remediation for those 330 cavities already installed in CEBAF will be presented.
 
slides icon Slides THOBB01 [16.521 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THOBB01  
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