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Champion, M. S.

Paper Title Page
MOPAS078 Digital RF Control for Spallation Neutron Source Accumulator Ring 611
 
  • H. Ma, M. S. Champion, M. T. Crofford, T. W. Hardek, K.-U. Kasemir, M. F. Piller, Y. Zhang
    ORNL, Oak Ridge, Tennessee
 
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U. S. Department of Energy.

The proposed upgrade plan for RF control of the Spallation Neutron Source (SNS) accumulator ring requires that the new digital field control module (FCM) support both the conventional narrow-band feed forward control and a new beam-based feed forward control. Both are necessary for compensating the heavy beam loading in SNS ring. The ring FCM also has the integrated control and monitoring features for the cavity bias, cavity resonance, and tetrode grid boost. A user-friendly Epics GUI for all these FCM functionalities is also a part of the requirement. The ring FCM under development is being implemented on the hardware of the proven FCM of SNS Linac. Both the controller architecture and the design code of the digital hardware for the Linac system will be largely reused in the ring system.

 
WEPMS072 Status and Performance of the Spallation Neutron Source Superconducting Linac 2502
 
  • I. E. Campisi, S. Assadi, F. Casagrande, M. S. Champion, M. T. Crofford, G. W. Dodson, J. Galambos, M. Giannella, S. Henderson, M. P. Howell, Y. W. Kang, K.-U. Kasemir, S.-H. Kim, Z. Kursun, P. Ladd, H. Ma, D. Stout, W. H. Strong, Y. Zhang
    ORNL, Oak Ridge, Tennessee
 
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U. S. Department of Energy

The Superconducting Linac at SNS has been operating with beam for almost two years. As the first operational pulsed superconducting linac, many of the aspect of its performance were unknown and unpredictable. A lot of experience has been gathered during the commissioning of its components, during the beam turn on and during operation at increasingly higher beam power. Some cryomodules have been cold for well over two years and have been extensively tested. The operation has been consistently conducted at 4.4 K and 10 and 15 pulses per second, with some cryomodules tested at 30 and 60 pps and some tests performed at 2 K. Careful balance between safe operational limits and the study of conditions, parameters and components that create physical limits has been achieved. This paper presents the experience and the performance of the superconducting cavities and of the associated systems with and without beam.

 
WEPMS074 Design and High Power Processing of RFQ Input Power Couplers 2505
 
  • Y. W. Kang, A. V. Aleksandrov, D. E. Anderson, 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
 
  Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U. S. Department of Energy.

A RF power coupling system has been developed for future upgrade of input coupling of the RFQ in the SNS linac. The design employs two coaxial loop couplers for 402.5 MHz operation. Each loop is fed through a coaxial ceramic window that is connected to an output of a magic-T waveguide hybrid through a coaxial to waveguide transition. The coaxial loop couplers are designed, manufactured, and high power processed. Two couplers will be used in parallel to power the accelerating structure with up to total 800 kW peak power at 8% duty cycle. RF and mechanical properties of the couplers are discussed. Result of high power RF conditioning that is performed in the RF test facility of the SNS is presented.

 
WEPMS075 Development and Testing of High Power RF Vector Modulators 2508
 
  • Y. W. Kang, M. S. Champion, T. W. Hardek, S.-H. Kim, M. P. McCarthy, A. V. Vassioutchenko, J. L. Wilson
    ORNL, Oak Ridge, Tennessee
 
  Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U. S. Department of Energy.

High power vector modulators can allow a fan-out RF power distribution system that can power many accelerating cavities from a single high-power klystron amplifier. The configuration enables independent control of amplitudes and phases of RF voltages at the cavities. A vector modulator employs either one or two hybrids with two fast phase shifters. Prototype high power RF vector modulators employing a hybrid and two fast ferrite phase shifters in coaxial TEM transmission lines for 402.5 MHz and 805 MHz are built and tested. RF properties of the design and result of high power testing are presented.

 
WEPMS081 Simulation and Initial Test Result of the SNS Ring RF System 2520
 
  • Y. Zhang, M. S. Champion, P. Chu, S. M. Cousineau, V. V. Danilov, T. W. Hardek, J. A. Holmes, H. Ma, M. F. Piller, M. A. Plum
    ORNL, Oak Ridge, Tennessee
 
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U. S. Department of Energy

A simulation code has been developed for the study of the Spallation Neutron Source (SNS) ring RF control. The code uses the time-domain solvers to compute beam-cavity interactions, and FFT methods to simulate time responses of the linear RF system. The important ingredients of the system are considered in the simulation model, which include the beam loading, dynamic cavity detuning, circuit bandwidth, loop delay, proportional-integral (P-I) controller for feedback and adaptive feed forward, stochastic noise, with-in-turn RF parameter change, beam current fluctuation and beam bunch leakage, etc. The beam loss in the accumulation ring goes up as the beam power increases, and thus a precise control of bunching voltage phase and amplitude is required to limit beam loss. This simulation tool will help the development a correct RF control and to achieve the goal of minimizing the beam loss.

 
FRXC01 SNS RF System Performance and Operation 3792
 
  • M. S. Champion
    ORNL, Oak Ridge, Tennessee
 
  The Spallation Neutron Source (SNS) Linac and Accumulator Ring utilize 100 Radio-Frequency (RF) systems for acceleration and bunching of the proton beam. Several different types of gridded tubes and klystrons are operated at 1, 2, 402.5 and 805 MHz, at power levels ranging from a few kilowatts to several megawatts to drive several types of accelerating cavities, both normal- and super-conducting. The RF systems are standardized, especially in the Linac, to ease operation and maintenance. Phase and amplitude control is achieved with a digital low-level RF control system. The RF systems operate reliably and support production of a high-quality low-loss proton beam. Various modifications and upgrades have been made or are in progress to enhance system reliability and performance. Planning is well underway for a power upgrade that will require an additional 36 RF systems.  
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FROAC01 The Spallation Neutron Source Accumulator Ring RF System 3795
 
  • T. W. Hardek, M. S. Champion, M. T. Crofford, H. Ma, M. F. Piller
    ORNL, Oak Ridge, Tennessee
  • K. Smith, A. Zaltsman
    BNL, Upton, Long Island, New York
 
  Funding: SNS is managed by UT-Batelle, LLC, under contract DE-AC05-00OR22725 for the U. S. Department of Energy.

The Spallation Neutron Source (SNS) accumulator ring is a fixed-frequency proton storage ring located at the output of the SNS Linear Accelerator (Linac). Its purpose is to convert 1 millisecond H- beam pulses from the SNS Linac into high-intensity 695 nanosecond pulses of protons for delivery to the neutron target. The RF bunching system controls longitudinal beam distribution during the accumulation process and maintains a 250+ nanosecond gap required for beam extraction. The RF system consists of three stations which operate at a beam revolution frequency of 1.05 MHz while a fourth station provides a second harmonic component at 2.1 MHz. The beam pulse at extraction consists of 1.6·1014 protons representing a peak beam current of 52 amperes. The system utilizes four 600kW tetrodes to provide the RF current necessary to produce the 40kV peak-bunching voltage and to control phase and amplitude at this high beam current. In this paper we review the design concepts incorporated into this heavily beam-loaded RF system and discuss its commissioning status.

 
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