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Champion, M. S.

Paper Title Page
TUP083 Development of High-Power RF Vector Modulator Employing TEM Ferrite Phase Shifters 451
 
  • Y. W. Kang, M. S. Champion, S.-H. Kim, M. P. McCarthy, A. V. Vassioutchenko, J. L. Wilson
    ORNL, Oak Ridge, Tennessee
  
  Construction and installation of cavity RF power distribution system in a high power superconducting RF accelerator can have cost savings if a fan-out configuration that feeds many cavities with a single high power klystron is realized. The configuration however requires independent control of RF amplitudes and phases to the cavities to perform properly. A prototype high power RF vector modulator for the control is built and tested. The vector modulator employs a quadrature hybrid and two fast ferrite phase shifters in square coaxial TEM transmission lines. The square coaxial format can provide the power handling capability and thermal stability. RF properties of the design and result of high power system testing of the design are presented.  
THP004 Digital Low-Level RF Control Using Non-IQ Sampling 568
 
  • L. R. Doolittle
    LBNL, Berkeley, California
  • M. S. Champion, H. Ma
    ORNL, Oak Ridge, Tennessee
  
  The success of digital feedback with synchronous IQ sampling for cavity field control in recent accelerator projects make this LLRF control scheme a popular choice. This short-period synchronous sampling does not, however, average out well-known defects in modern ADC and DAC hardware. That limits the achievable control precision for digital IQ LLRF controllers, while demands for precision are increasing for future accelerators such as International Linear Collider. For this reason, a collaborative effort is developing a digital LLRF control evaluation platform to experiment using coherent sampling with much longer synchronous periods, on the order of the cavity closed-loop bandwidth. This exercise will develop and test the hardware and software needed to meet greater future RF control challenges.  
THP005 Digital Control of Cavity Fields in the Spallation Neutron Source Superconducting Linac 571
 
  • H. Ma, M. S. Champion, M. T. Crofford, K.-U. Kasemir, M. F. Piller
    ORNL, Oak Ridge, Tennessee
  • A. Brandt
    DESY, Hamburg
  • L. R. Doolittle, A. Ratti
    LBNL, Berkeley, California
  
  Control of the pulsed RF cavity fields in the Spallation Neutron Source (SNS) superconducting Linac uses both the real-time feedback regulation and the pulse-to-pulse adaptive feed-forward compensation. This control combination is required to deal with the typical issues associated with superconducting cavities, such as the Lorentz force detuning, mechanical resonance modes, and cavity filling. The all-digital implementation of this system provides the capabilities and flexibility necessary for achieving the required performance, and to accommodate the needs of various control schemes. The low-latency design of the digital hardware has successfully produced a wide control bandwidth, and the developed adaptive feed forward algorithms have proved to be essential for the controlled cavity filling, the suppression of the cavity mechanical resonances, and the beam loading compensation. As of this time, all 96 LLRF systems throughout the Linac have been commissioned and are in operation.  
THP029 Development of an RFQ Input Power Coupling System 634
 
  • Y. W. Kang, A. V. Aleksandrov, M. M. Champion, M. S. Champion, M. T. Crofford, P. E. Gibson, T. W. Hardek, P. Ladd, M. P. McCarthy, D. Stout, A. V. Vassioutchenko
    ORNL, Oak Ridge, Tennessee
  • H. L. Haenichen
    TU Darmstadt, Darmstadt
  
  An RF input coupler system is designed, manufactured, and tested for future upgrade of the coupling system of the RFQ in the SNS linac. The design employs two coaxial loops in vacuum side of two coaxial ceramic windows through coaxial transmission lines that are connected to a magic-T waveguide power splitter for 402.5 MHz operation. The couplers will be used with up to total 800 kW peak power at 8% duty cycle. RF properties of the system and fabricated structure along with vacuum and thermal properties are discussed. Two couplers are joined together through an evacuated bridge waveguide for high power RF processing. Result of the high power conditioning that is performed in the RF test facility of the SNS is presented.  
THP081 Study on Fault Scenarios of Coaxial Type HOM Couplers in SRF Cavities 770
 
  • S.-H. Kim, I. E. Campisi, F. Casagrande, M. S. Champion, M. T. Crofford, D.-O. Jeon, Y. W. Kang, M. P. McCarthy, D. Stout
    ORNL, Oak Ridge, Tennessee
  
  Coaxial type couplers are adopted in many superconducting radio-frequency (SRF) cavities to suppress higher order modes for beam dynamics and cryogenic loads issues. HERA (Hadron-Electron Ring Accelerator) and TTF (Tesla Test Facility) are equipped with this type coupler and showed successful performances. It is, however, under suspicion that a limitation or a fault could be initiated from this type of coupler at certain combinations between cavity operating conditions and engineering designs of the coupler. Some possible scenarios are summarized and also some observations in the SNS (Spallation Neutron Source) SRF cavities are also reported.