Author: Romanenko, A.
Paper Title Page
MOPP018 Nitrogen-Doped 9-Cell Cavity Performance in the Cornell Horizontal Test Cryomodule 88
 
  • D. Gonnella, R.G. Eichhorn, F. Furuta, G.M. Ge, D.L. Hall, Y. He, G.H. Hoffstaetter, M. Liepe, T.I. O'Connel, S. Posen, P. Quigley, J. Sears, V. Veshcherevich
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • A. Grassellino, A. Romanenko
    Fermilab, Batavia, Illinois, USA
  
  Funding: U.S. Department of Energy
Cornell has recently completed construction and qualification of a horizontal cryomodule capable of holding a 9-cell ILC cavity. A nitrogen-doped niobium 9-cell cavity was assembled into the Horizontal Test Cryomodule (HTC) with a high Q input coupler and tested. We report on results from this test of a nitrogen-doped cavity in cryomodule and discuss the effects of cool down rate and thermal cycling on the residual resistance of the cavity. 		 
 
TUIOC02
 Breakthrough technology for very high quality factors in SCRF cavities  
 
  • A. Romanenko
    Fermilab, Batavia, Illinois, USA
  
  Recently, a new technology for processing SRF cavities was developed at Fermilab, which allows to achieve quality factors (Q) several times higher than those obtained by any other state-of-the-art cavity processing techniques. It is of direct and primary importance for all planned CW accelerators such as LCLS-II, PIP-II, and others since higher Q directly translates into lower wall dissipated power and hence much lower capital and operational costs for the refrigeration system. The technology is based on the slight modification to the standard vacuum degassing at 800C by performing its final part in the small partial pressure of nitrogen. In this talk we will present the most effective and robust recipes developed for single and multicell cavities, and discuss possible underlying physical mechanisms of the drastic Q improvement as deduced by different structural (SIMS, cryo-TEM) and superconducting (LE-muSR, PCT) probes.  
slides icon Slides TUIOC02 [2.717 MB]  
 
THPP124 Wakefields in the Superconducting RF Cavities of LCLS-II 1147
 
  • K.L.F. Bane, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  • A. Romanenko, V.P. Yakovlev
    Fermilab, Batavia, Illinois, USA
  
  Funding: Work supported by Department of Energy contract DE–AC02–76SF00515.
The superconducting cavities in the linacs of LCLS-II are designed to operate at 2K, where cooling costs are very expensive. In addition to an unavoidable static load and the dynamic load of the fundamental 1.3 GHz accelerating rf, there will be higher order mode (HOM) power deposited by the beam. Due to the very short bunch length the LCLS-II beam spectrum extends into the THz range. Ceramic absorbers, cooled to 70K and located between cryomodules, are meant to absorb much of this power; understanding their effectiveness, however, is a challenging task. In this report we calculate the amount of power radiated by the beam in the different portions of the linac as the bunch length is changed by the bunch compressors. We consider both the steady state radiation as well as transients that arise at the beginning of the linac structures. In addition, transitions due to changes in the vacuum chamber aperture at the ends of the linacs are also considered. Finally, under the assumption that all the wake power ends up in the SRF cavity walls, we estimate the wall heating and the possibility of breaking the Cooper pairs and quenching the cavities.