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England, R. J.

Paper Title Page
THPMS020 Beam-Driven Dielectric Wakefield Accelerating Structure as a THz Radiation Source 3041
  • A. M. Cook, H. Badakov, R. J. England, J. B. Rosenzweig, R. Tikhoplav, G. Travish, O. Williams
    UCLA, Los Angeles, California
  • A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio
  • M. C. Thompson
    LLNL, Livermore, California
  Funding: United States Department of Energy

Experimental work is planned to study the performance of a beam-driven cylindrical dielectric wakefield accelerating structure as a source of THz coherent Cerenkov radiation. For an appropriate choice of dielectric tube geometry and driving electron bunch parameters, the device operates in a single-mode regime, producing narrow-band radiation in the THz range. This source can potentially produce high power levels relative to currently available sources, with ~50 μJ radiated energy per pulse achievable using the electron beam currently in operation at the Neptune Advanced Accelerator Research Laboratory at UCLA (~13 MeV beam energy, ~200 μm RMS bunch length, ~500 pC bunch charge). Preparations underway for installation of the experiment are discussed.

THPMS021 Optimum Electron Bunch Creation in a Photoinjector Using Space Charge Expansion 3044
  • J. B. Rosenzweig, A. M. Cook, M. P. Dunning, R. J. England, P. Musumeci
    UCLA, Los Angeles, California
  • M. Bellaveglia, M. Boscolo, G. Di Pirro, M. Ferrario, D. Filippetto, G. Gatti, L. Palumbo, C. Vicario
    INFN/LNF, Frascati (Roma)
  • L. Catani, A. Cianchi
    INFN-Roma II, Roma
  • S. M. Jones
    Jet Propulsion Laboratory, Pasadena, California
  Recent studies have shown that by illuminating a photocathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped electron bunch can be dynamically formed. Linear space-charge fields then exist in all dimensions inside of the bunch, which minimizes emittance growth. Here we study this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. We show that the two processes are compatible, with simulations indicating that a very high brightness beam can be obtained. An initial time-resolved experiment has been performed at the SPARC injector in Frascati, involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary experiment, as well as plans for future experiments to resolve the ellipsoidal bunch shape at low energy. Future measurements at high energy based on fs resolution RF sweepers are also discussed.  
FRPMS060 Commissioning of the UCLA Neptune X-Band Deflecting Cavity and Applications to Current Profile Measurement of Ramped Electron Bunches 4135
  • R. J. England, B. D. O'Shea, J. B. Rosenzweig, G. Travish
    UCLA, Los Angeles, California
  • D. Alesini
    INFN/LNF, Frascati (Roma)
  Funding: Department of Energy Grant # DE-FG02-92ER40693

A 9-cell standing wave deflecting cavity has recently been constructed and installed at the UCLA Neptune Laboratory for use as a temporal diagnostic for the 13 MeV, 300 to 700 pC electron bunches generated by the Neptune photoinjector beamline. The cavity is a center-fed Glid-Cop structure operating in at TM110-like deflecting mode at 9.59616 GHz with a pi phase advance per cell. At the maximum deflecting voltage of 500 kV, the theoretical resolution limit of the device is 50 fs, although with current beam parameters and a spot size of 460 microns RMS the effective resolution is approximately 400 fs. We discuss the operation and testing of the cavity as well as its intended application: measuring the temporal current profile of ramped electron bunches generated using the Neptune dogleg compressor, and we present the first measurements of the electron beam current profile obtained using the deflecting cavity.