Author: Ross, M.C.
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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WEPRI067 Multi-Physics Analysis of CW Superconducting Cavity for the LCLS-II using ACE3P 2645
 
  • Z. Li, C. Adolphsen, O. Kononenko, T.O. Raubenheimer, C.H. Rivetta, M.C. Ross, L. Xiao
    SLAC, Menlo Park, California, USA
  
  Funding: Work was supported by the U.S. DOE contract DE-AC02-76SF00515 and used the resources of NERSC at LBNL under US DOE Contract No. DE-AC03-76SF00098.
The LCLS-II linac utilizes superconducting technology operating at continuous wave to accelerate the 1-MHz electron beams to 4 GeV to produce tunable FELs. The TESLA 9-cell superconducting cavity is adopted as the baseline design for the linac. The design gradient is approximately 16 MV/m. The highest operating current is 300 μA. Assuming that the RF power is matched at the highest current, the optimal loaded QL of the cavity is found to be around 4·107. Because of the high QL, the cavity bandwidth approaches the background microphonic detuning, and the performance of the cavity is tightly coupled to the mechanical perturbations of the cavity/cryomodule system. The resulting large phase and amplitude variations in the cavity require active feedback to achieve the 0.01% amplitude and phase stability requirements. To understand the cavity RF response and feedback requirements to the microphonics and Lorentz Force detuning, we have developed a simulation model of the RF-mechanical coupled system using parameters obtained with the multi-physics solver ACE3P. We will present the simulation results of the LCLS-II linac under different power feed scenarios and feedback schemes. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI067  
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