Author: Gonnella, D.
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WEPMK012 Update on Plasma Processing R&D for LCLS-II 2656
  • P. Berrutti, A. Grassellino, T.N. Khabiboulline, M. Martinello
    Fermilab, Batavia, Illinois, USA
  • M. Doleans, S.-H. Kim, K.E. Tippey
    ORNL, Oak Ridge, Tennessee, USA
  • D. Gonnella, G. Lanza, M.C. Ross
    SLAC, Menlo Park, California, USA
  Funding: Fermi Research Alliance, LLC, under Contract DE-AC02-07CH11359 with the U.S. DOE
SRF cavities performance preservation is crucial, from vertical test to accelerator operation. Field emission is still one of the main problems to overcome and plasma cleaning has been proven successful by SNS, in cleaning field emitters and increasing the work function of Nb. A collaboration has been established between FNAL, SLAC and ORNL with the purpose of applying plasma processing to LCLS-II cavities, in order to minimize and overcome field emission without affecting the high Q of N-doped cavities. The recipe will follow the neon-oxygen active plasma adopted at SNS, allowing in-situ processing of cavities and cryomodules from hydrocarbon contaminants. A novel method for plasma ignition has been developed at FNAL: a plasma glow discharge is ignited using high order modes to overcome limitations imposed by the fundamental power coupler. The results of experiments on 9-cell LCLS-II cavity are presented, along with plasma ignition studies. In addition the RF system is shown and N-doped Nb samples studies are discussed.
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THPAL140 Rework Recipe Development, Analysis and Results of Select 9-Cell Cavities for LCLS-II 3968
  • A.D. Palczewski, K. Macha, H. Park, C.E. Reece, K.M. Wilson
    JLab, Newport News, Virginia, USA
  • A. Burrill, D. Gonnella
    SLAC, Menlo Park, California, USA
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The SLAC National Accelerator Laboratory is currently constructing a major upgrade to its accelerator, the Linac Coherent Light Source II (LCLS-II). Several Department of Energy laboratories, including the Thomas Jefferson National Accelerator Facility (JLab) and Fermi National Accelerator Laboratory (FNAL), are collaborating in this project. The cryomodules for this project each consist of eight 1.3-GHz cavities produced by two vendors, Research Instruments GmbH in Germany (RI*) and Ettore Zanon S.p.a. in Italy (EZ*), using niobium cell material from Tokyo Denkai Co., Ltd. (TD) and Ningxia Orient Tantalum Industry Co., Ltd. (OTIC/NX)). During the initial production run, cavity performance from one of the vendors (Vendor A) was far below expectation. All the cavities had low Q0, later attributed to minimal EP as well as high-flux-trapping NX material, early quench behaviour below 18 MV/m, with many having Q0 roll-off at 12-16 MV/m. Production was stopped multiple times over the following 6 months, with test batches of cavities being made to ascertain the root cause of the problem. The final root cause of the problem was found to be inappropriate grinding of the RF surface prior to welding which left normal conducting inclusions in the surface. In addition, most cavities showed internal and external weld spatter which required post weld grinding and a very rough surface from operating the electropolishing machine in an etching rather than polishing regime. All issues have been corrected on new cavities and rework is underway on the originally effected cavities.
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