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Horan, D.

Paper Title Page
TOAB009 Generation of Short X-Ray Pulses Using Crab Cavities at the Advanced Photon Source 668
 
  • K.C. Harkay, M. Borland, Y.-C. Chae, G. Decker, R.J. Dejus, L. Emery, W. Guo, D. Horan, K.-J. Kim, R. Kustom, D.M. Mills, S.V. Milton, G. Pile, V. Sajaev, S.D. Shastri, G.J. Waldschmidt, M. White, B.X. Yang
    ANL, Argonne, Illinois
  • A. Zholents
    LBNL, Berkeley, California
 
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

There is growing interest within the user community to utilize the pulsed nature of synchrotron radiation from storage ring sources. Conventional third-generation light sources can provide pulses on the order of 100 ps but typically cannot provide pulses of about 1 ps that some users now require to advance their research programs. However, it was recently proposed by A. Zholents et al. to use rf orbit deflection to generate subpicosecond X-ray pulses.* In this scheme, two crab cavities are used to deliver a longitudinally dependent vertical kick to the beam, thus exciting longitudinally correlated vertical motion of the electrons. This makes it possible to spatially separate the radiation coming from different longitudinal parts of the beam. An optical slit can then be used to slice out a short part of the radiation pulse, or an asymetrically cut crystal can be used to compress the radiation in time. In this paper, we present a feasibility study of this method applied to the Advanced Photon Source. We find that the pulse length can be decreased down to a few-picosecond range using superconducting crab cavities.

*A. Zholents et al., NIM A 425, 385 (1999).

 
TPPT035 High-Power RF Testing of a 352-MHz Fast-Ferrite RF Cavity Tuner at the Advanced Photon Source 2407
 
  • D. Horan, E.E. Cherbak
    ANL, Argonne, Illinois
 
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under contract No. W-31-109-ENG-38.

A 352-MHz fast-ferrite rf cavity tuner, manufactured by Advanced Ferrite Technology, was high-power tested on a single-cell copper rf cavity at the Advanced Photon Source. These tests measured the fast-ferrite tuner performance in terms of power handling capability, tuning bandwidth, tuning speed, stability, and rf losses. The test system comprises a single-cell copper rf cavity fitted with two identical coupling loops, one for input rf power and the other for coupling the fast-ferrite tuner to the cavity fields. The fast-ferrite tuner rf circuit consists of a cavity coupling loop, a 6-1/8” EIA coaxial line system with directional couplers, and an adjustable 360° mechanical phase shifter in series with the fast-ferrite tuner. A bipolar DC bias supply, controlled by a low-level rf cavity tuning loop consisting of an rf phase detector and a PID amplifier, is used to provide a variable bias current to the tuner ferrite material to maintain the test cavity at resonance. Losses in the fast-ferrite tuner are calculated from cooling water calorimetry. Test data will be presented.

 
TPPT036 Higher-Order-Mode Damper Testing and Installation in the Advanced Photon Source 352-MHz Single-Cell RF Cavities 2443
 
  • G.J. Waldschmidt, N.P. Di Monte, D. Horan, L.H. Morrison, G. Pile
    ANL, Argonne, Illinois
 
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

Higher-order-mode dampers were recently installed in the storage ring rf cavities at the Advanced Photon Source to eliminate longitudinal coupled-bunch instability. It was discovered that the 540-MHz cavity dipole mode created beam instability at beam currents in excess of 85 mA causing horizontal emittance blowup. Methods of compensating for the instability by detuning the cavities and adjusting the cavity water temperature were becoming more difficult at higher beam currents as tests were performed to prepare for eventual 300-mA beam current operation. Electric field passive dampers located on the median plane of each cavity were determined to be the most promising solution. Simulation models were created and verified with low-power testing of the dampers. High-power testing of the dampers as well as conditioning of the damper ceramic load were also performed at the APS 352-MHz rf test stand and compared with simulation results. Preliminary test results will be discussed.