Author: Neubauer, M.L.
Paper Title Page
MOP046 RF Breakdown Studies Using Pressurized Cavities 184
 
  • R. Sah, A. Dudas, R.P. Johnson, M.L. Neubauer
    Muons, Inc, Batavia, USA
  • M. BastaniNejad, A.A. Elmustafa
    Old Dominion University, Norfolk, Virginia, USA
  • J.M. Byrd, D. Li
    LBNL, Berkeley, California, USA
  • M.E. Conde, W. Gai
    ANL, Argonne, USA
  • A. Moretti, M. Popovic, K. Yonehara
    Fermilab, Batavia, USA
  • D. Rose
    Voss Scientific, Albuquerque, New Mexico, USA
 
  Funding: Supported in part by USDOE STTR Grant DE-FG02-08ER86352 and FRA DOE Contract DE-AC02-07CH11359
Many present and future particle accelerators are limited by the maximum electric gradient and peak surface fields that can be realized in RF cavities. Despite considerable effort, a comprehensive theory of RF breakdown has not been achieved, and mitigation techniques to improve practical maximum accelerating gradients have had only limited success. Recent studies have shown that high gradients can be achieved quickly in 805 MHz RF cavities pressurized with dense hydrogen gas without the need for long conditioning times, because the dense gas can dramatically reduce dark currents and multipacting. In this project we use this high pressure technique to suppress effects of residual gas and geometry found in evacuated cavities to isolate and study the role of the metallic surfaces in RF cavity breakdown as a function of radiofrequency and surface preparation. A 1.3-GHz RF test cell with replaceable electrodes (e.g. Mo, Cu, Be, W, and Nb) has been built, and a series of detailed experiments is planned at the Argonne Wakefield Accelerator. These experiments will be followed by additional experiments using a second test cell operating at 402.5 MHz.
 
 
TUP083 Phase and Frequency Locked Magnetrons for SRF Sources 979
 
  • M. Popovic, A. Moretti
    Fermilab, Batavia, USA
  • M.A.C. Cummings, A. Dudas, R.P. Johnson, M.L. Neubauer, R. Sah
    Muons, Inc, Batavia, USA
 
  Funding: Supported in part by STTR Grant DE-SC0002766
In order to make use of ferrite and/or garnet materials in the phase and frequency locked magnetron, for which Muons, Inc., received a Phase II award, materials must be tested in two orthogonal magnetic fields. One field is from the biasing field of the magnetron, the other from the biasing field used to control the ferrite within the anode structure of the magnetron. A test fixture was built and materials are being tested to determine their suitability. The status of those material tests are reported on in this paper.
 
 
TUP092 Multi-purpose 805 MHz Pillbox RF Cavity for Muon Acceleration Studies 1003
 
  • G.M. Kazakevich, G. Flanagan, R.P. Johnson, M.L. Neubauer, R. Sah
    Muons, Inc, Batavia, USA
  • K.C.D. Chan, A.J. Jason, S.S. Kurennoy, H.M. Miyadera, P.J. Turchi
    LANL, Los Alamos, New Mexico, USA
  • A. Moretti, M. Popovic, K. Yonehara
    Fermilab, Batavia, USA
  • Y. Torun
    IIT, Chicago, Illinois, USA
 
  Funding: Supported by DOE grant DE-FG-08ER86352.
An 805 MHz RF pillbox cavity has been designed and constructed to investigate potential muon beam acceleration and cooling techniques. The cavity can operate in vacuum or under pressure to 100 atmospheres, at room temperature or in an LN2 bath at 77 K. The cavity is designed for easy assembly and disassembly with bolted construction using aluminum seals. The surfaces of the end walls of the cavity can be replaced with different materials such as copper, aluminum, beryllium, or molybdenum, and with different geometries such as shaped windows or grid structures. Different surface treatments such as electro polished, high-pressure water cleaned, and atomic layer deposition are being considered for testing. The cavity has been designed to fit inside the 5-Tesla solenoid in the MuCool Test Area at Fermilab. Performance of the cavity, including initial conditioning and operation in the external magnetic field will be reported.
 
 
TUP094 Novel Crab Cavity RF Design 1006
 
  • M.L. Neubauer, A. Dudas, R. Sah
    Muons, Inc, Batavia, USA
  • R.A. Rimmer, H. Wang
    JLAB, Newport News, Virginia, USA
 
  Funding: Supported in part by DOE SBIR grant DE-SC0005444
A 20-50 MV integrated transverse voltage is required for the Electron-Ion Collider. The most promising of the crab cavity designs that have been proposed in the last five years are the TEM type crab cavities because of the higher transverse impedance. The TEM design approach is extended here to a hybrid crab cavity that includes the input power coupler as an integral part of the design. A prototype was built with Phase I monies and tested at JLAB. The results reported on, and a system for achieving 20-50 MV is proposed.
 
 
TUP095 Adjustable High Power Coax Coupler without Moving Parts 1009
 
  • M.L. Neubauer, A. Dudas, R. Sah
    Muons, Inc, Batavia, USA
  • R. Nassiri
    ANL, Argonne, USA
 
  An RF power coupler is designed to operate without moving parts. This new concept for an adjustable coupler is applicable to operation at any radiofrequency. CW operation of such a coupler is especially challenging at lower frequencies. The basic component of the coupler is a ferrite tuner. The RF coupler has no movable parts and relies on a ferrite tuner assembly, coax TEE, and double windows to provide a VSWR of better than 1.05:1 and a bandwidth of at least 8 MHz at 1.15:1. The ferrite tuner assembly on the stub end of the coax TEE uses an applied DC magnetic field to change the Qext and the RF coupling coefficient between the RF input and the cavity. Recent work in making measurements of the loss in the ferrite and likely thermal dissipation required for 100 kW CW operation is presented.  
 
TUP096 Beam Pipe HOM Absorber for SRF Cavities 1012
 
  • R. Sah, A. Dudas, M.L. Neubauer
    Muons, Inc, Batavia, USA
  • G.H. Hoffstaetter, M. Liepe, H. Padamsee, V.D. Shemelin
    CLASSE, Ithaca, New York, USA
  • K. Ko, C.-K. Ng, L. Xiao
    SLAC, Menlo Park, California, USA
 
  Funding: Supported in part by DOE SBIR grant DE-SC0002733 and USDOE Contract No. DE-AC05-84-ER-40150.
Superconducting RF (SRF) systems typically contain resonances at unwanted frequencies, or higher order modes (HOM). For storage ring and linac applications, these higher modes must be damped by absorbing them in ferrite and other lossy ceramic materials. Typically, these absorbers are brazed to substrates that are often located in the drift tubes adjacent to the SRF cavity. These HOM absorbers must have broadband microwave loss characteristics and must be thermally and mechanically robust, but the ferrites and their attachments are weak under tensile and thermal stresses and tend to crack. Based on prior work on HOM loads for high current storage rings and for an ERL injector cryomodule, a HOM absorber with improved materials and design is being developed for high-gradient SRF systems. This work will use novel construction techniques (without brazing) to maintain the ferrite in mechanical compression. Attachment techniques to the metal substrates will include process techniques for fully-compressed ferrite rings. Prototype structures will be fabricated and tested for mechanical strength under thermal cycling conditions.
 
 
THP203 Improved Inverted DC Gun Insulator Assembly 2501
 
  • M.L. Neubauer, A. Dudas, R. Sah
    Muons, Inc, Batavia, USA
 
  Funding: Work supported in part by USDOE Contract No. DE-AC05-84-ER-40150.
High gradient DC guns are currently being developed with inverted ceramic insulators in order to avoid failure of the insulators from field emission and charge build-up. Our goal is to increase the DC voltages from 250 kV to 500 kV in these inverted ceramic DC Gun insulator assemblies. To achieve reliability, the arc-path gradient along the length of the insulator ceramic at the interface with the dielectric material should be lower than 500 kV/m (13 V/mil). In order to achieve this low arc-path gradient, a novel extended inverted insulator ceramic is being developed. Novel assembly processes are being developed for the high voltage connector, so that the interface between the connector dielectric and the surface of the extended inverted ceramic insulator will be void free. A complete DC Gun Inverted Ceramic Insulator Assembly will be designed and fabricated for reliable 500 kV DC operation.