Author: Hoffstaetter, G.H.
Paper Title Page
MOPRO113 Beam-based HOM Measurements in Cornell's ERL Main Linac Cavity 359
 
  • D.L. Hall, A.C. Bartnik, M.G. Billing, D. Gonnella, G.H. Hoffstaetter, M. Liepe, C.E. Mayes
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  A search for HOMs in Cornell’s ERL main linac cavity installed in a Horizontal Test Cryomodule (HTC) has been carried out using a bunch charge modulation method, as part of the effort towards building an Energy Recovery Linac (ERL). The beam-based HOM measurements offer the significant advantage of being able to detect trapped modes invisible to both the RF pickup probes and HOM damping loads, and allow for measuring the R/Q of the modes. For each HOM detected during the search, measurements were taken to determine its nature (monopole, dipole, etc.), frequency, loaded quality factor and shunt impedance. A selection of the most notable modes found is presented, compared to 3D HOM simulations, and their potential impact on the BBU current of the future Cornell ERL is discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-MOPRO113  
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WEPRI061 Cornell's Main Linac Cryomodule for the Energy Recovery Linac Project 2624
 
  • R.G. Eichhorn, B. Bullock, J.V. Conway, B. Elmore, F. Furuta, Y. He, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, T.I. O'Connel, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Cornell University has been designing and building superconducting accelerators for various applications for more than 50 years. Currently, an energy-recovery linac (ERL) based synchrotron-light facility is proposed making use of the existing CESR facility. As part of the phase 1 R&D program funded by the NSF, critical challenges in the design were addressed, one of them being a full linac cryo-module. It houses 6 superconducting cavities- operated at 1.8 K in continuous wave (CW) mode - with individual HOM absorbers and one magnet/ BPM section. Pushing the limits, a high quality factor of the cavities (2•1010) and high beam currents (100 mA accelerated plus 100 mA decelerated) are targeted. We will present the status of the main linac cryomodule (MLC) fabrication and the findings on the cavity performance and component testing.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI061  
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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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THPRO053 Ion Effects in the Cornell ERL High Intensity Photoinjector 2989
 
  • S.J. Full, A.C. Bartnik, I.V. Bazarov, J. Dobbins, B.M. Dunham, G.H. Hoffstaetter
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  We present our first measurements of trapped ions in the Cornell energy recovery linac (ERL) photoinjector. During high intensity operation, ions become trapped inside of the electric potential generated by the electron beam and oscillate transversely with a characteristic frequency. At high beam currents, electron beam-ion interactions result in excessive radiation, primarily due to beam losses and bremsstrahlung. However, by shaking the beam at the trapped ion's oscillation frequency, we are able to drive a resonance that severely reduces or eliminates this radiation. This both confirms the viability of beam shaking as an ion mitigation strategy inside high intensity injectors, and allows us to measure the trapped ion oscillation frequencies indirectly. Experimental data for a beam energy of 5 MeV, a bunch repetition rate of 1.3 GHz, and beam currents up to 20 mA, as well as simulations to describe our data and the beam shaking principle are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO053  
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