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Rimmer, R.A.

Paper Title Page
MOPCH182 The JLAB Ampere-class Cryomodule Conceptual Design 490
 
  • R.A. Rimmer, G. Ciovati, E. Daly, T. Elliott, J. Henry, W.R. Hicks, P. Kneisel, S. Manning, R. Manus, J.P. Preble, K. Smith, M. Stirbet, L. Turlington, L. Vogel, H. Wang, K. Wilson, G. Wu
    Jefferson Lab, Newport News, Virginia
  
  For the next generation of compact high-power FELs a new cryomodule is required that is capable of accelerating up to Ampere levels of beam current. Challenges include strong HOM damping, high HOM power and high fundamental-mode power (in operating scenarios without full energy recovery). For efficient use of space a high real-estate gradient is desirable and for economic operation good fundamental-mode efficiency is important. The technology must also be robust and should be based on well-proven and reliable technologies. For Ampere-class levels of beam current both halo interception and beam break-up (BBU) are important considerations. These factors tend to drive the designs to lower frequencies where the apertures are larger and the transverse impedances are lower. To achieve these goals we propose to use a compact waveguide-damped multi-cell cavity packaged in an SNS-style cryomodule.  
TUPCH133 Comparison of Measured and Calculated Coupling between a Waveguide and an RF Cavity Using CST Microwave Studio 1328
 
  • J. Shi, H. Chen, S. Zheng
    TUB, Beijing
  • D. Li
    LBNL, Berkeley, California
  • R.A. Rimmer, H. Wang
    Jefferson Lab, Newport News, Virginia
  
  Accurate predications of RF coupling between an RF cavity and ports attached to it have been an important study subject for years for RF coupler and higher order modes (HOM) damping design. We report recent progress and a method on the RF coupling simulations between waveguide ports and RF cavities using CST Microwave Studio in time domain (Transit Solver). Comparisons of the measured and calculated couplings are presented. The simulated couplings and frequencies agree within ~ 10% and ~ 0.1% with the measurements, respectively. We have simulated couplings with external Qs ranging from ~ 100 to ~ 100, 000, and confirmed with measurements. The method should also work well for higher Qs, and can be easily applied in RF power coupler designs and HOM damping for normal-conducting and superconducting cavities.  
TUPCH145 The MUCOOL RF Program 1358
 
  • J. Norem
    ANL, Argonne, Illinois
  • A. Bross, A. Moretti, B. Norris, Z. Qian
    Fermilab, Batavia, Illinois
  • D. Li, S.P. Virostek, M.S. Zisman
    LBNL, Berkeley, California
  • R.A. Rimmer
    Jefferson Lab, Newport News, Virginia
  • R. Sandstrom
    DPNC, Genève
  • Y. Torun
    IIT, Chicago, Illinois
  
  Efficient muon cooling requires high RF gradients in the presence of high (~3T) solenoidal fields. The Muon Ionization Cooling Experiment (MICE) also requires that the x-ray production from these cavities is low, in order to minimize backgrounds in the particle detectors that must be located near the cavities. These cavities require thin Be windows to ensure the highest fields on the beam axis. In order to develop these cavities, the MUCOOL RF Program was started about 6 years ago. Initial measurements were made on a six-cell cavity and a single-cell pillbox, both operating at 805 MHz. We have now begun measurements of a 201 MHz pillbox cavity. This program has led to new techniques to look at dark currents, a new model for breakdown and a general model of cavity performance based on surface damage. The experimental program includes studies of thin Be windows, conditioning, dark current production from different materials, magnetic-field effects and breakdown. We will present results from measurements at both 805 and 201 MHz.  
TUPCH146 The Interactions of Surface Damage on RF Cavity Operation 1361
 
  • J. Norem, A. Hassanein, Z. Insepov
    ANL, Argonne, Illinois
  • A. Bross, A. Moretti, Z. Qian
    Fermilab, Batavia, Illinois
  • D. Li, M.S. Zisman
    LBNL, Berkeley, California
  • R.A. Rimmer
    Jefferson Lab, Newport News, Virginia
  • D.N. Seidman, K. Yoon
    NU, Evanston, Illinois
  • Y. Torun
    IIT, Chicago, Illinois
  
  Studies of low frequency RF systems for muon cooling has led to a variety of new techniques for looking at dark currents, a new model of breakdown, and, ultimately, a model of RF cavity operation based on surface damage. We find that cavity behavior is strongly influenced by the spectrum of enhancement factors on field emission sites. Three different spectra are involved: one defining the initial state of the cavity, the second determined by the breakdown events, and the third defining the equilibrium produced as a cavity operates at its maximum field. We have been able to measure these functions and use them to derive a wide variety of cavity parameters: conditioning behavior, material, pulse length, temperature, vacuum, magnetic field, pressure, gas dependence. In addition we can calculate the dependence of breakdown rate on surface field and pulse length. This work correlates with data from Atom Probe Tomography. We will describe this model and new experimental data.  
TUPCH148 201 MHz Cavity R&D for MUCOOL and MICE 1367
 
  • D. Li, S.P. Virostek, M.S. Zisman
    LBNL, Berkeley, California
  • A. Bross, A. Moretti, B. Norris
    Fermilab, Batavia, Illinois
  • J. Norem
    ANL, Argonne, Illinois
  • H.L. Phillips, R.A. Rimmer, M. Stirbet
    Jefferson Lab, Newport News, Virginia
  • M. Reep, D.J. Summers
    UMiss, University, Mississippi
  • Y. Torun
    IIT, Chicago, Illinois
  
  We describe the design, fabrication and preliminary testing of the prototype 201 MHz copper cavity for a muon ionization cooling channel. Application of the cavity includes the Muon Ionization Cooling Experiment (MICE) as well as cooling channels for a neutrino factory or a muon collider. This cavity was developed by the US MUCOOL collaboration and is being tested in the MUCOOL Test Area (MTA) at Fermilab. In order to achieve a high accelerating gradient, the cavity beam irises are terminated by a pair of curved, thin beryllium windows. Several of the fabrication methods developed for this cavity and the windows are novel and offer significant cost savings compared to conventional construction methods. Cavity thermal and RF performance will be compared to FEA modeling predictions. RF commissioning results will be presented.