Author: Gai, W.
Paper Title Page
MOPPP012 Experimental Observation of Energy Modulation in Electron Beams Passing through Terahertz Dielectric Wakefield Structures 595
 
  • S.P. Antipov, C.-J. Jing, A. Kanareykin, P. Schoessow
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • M.G. Fedurin, K. Kusche, V. Yakimenko
    BNL, Upton, Long Island, New York, USA
  • W. Gai, A. Zholents
    ANL, Argonne, USA
  • B.C. Jiang
    SINAP, Shanghai, People's Republic of China
 
  Funding: DOE SBIR.
We report observation of a strong wakefield induced energy modulation in an energy-chirped electron bunch passing through a terahertz dielectric-lined waveguide. This modulation can be effectively converted into a spatial modulation by means of a chicane, forming micro-bunches (density modulation) with a periodicity of 0.5 - 1 picosecond, hence capable of driving coherent THz radiation. The experimental results agree well with theoretical predictions.
 
 
MOPPP013 Passive Momentum Spread Compensation by a “Wakefield Silencer” 598
 
  • S.P. Antipov, C.-J. Jing, A. Kanareykin, P. Schoessow
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • M.G. Fedurin, K. Kusche, V. Yakimenko
    BNL, Upton, Long Island, New York, USA
  • W. Gai, A. Zholents
    ANL, Argonne, USA
 
  Funding: DOE SBIR.
We report an observation of de-chirping of a linearly chirped (in energy) electron bunch by its passage through a 5 cm long dielectric loaded waveguide structure. The experiment was conducted at the ATF facility at BNL according to a concept dubbed a wakefield silencer originally developed at the ANL AATF*, which involves defining the electron bunch peak current distribution and selecting the optimal waveguide structure suitable for chirp cancellation using self-induced wakefields of the electron bunch. Our experiment has been carried out with a 247 micron triangular beam with a 200 keV energy spread, which was reduced by a factor of three to approximately 70 keV by passing it through a 0.95 THz dielectric-lined structure. Theoretical analysis supports the experimental results. Further exploration and applications of this technique will be discussed as well.
* M. Rosing, J. Simpson, Argonne Wakefield Accelerator Note, WF -144 (1990).
 
 
MOPPR068 Design and Development of the Diagnostic System for 75 MeV Electron Drive Beam for the AWA Upgrade 942
 
  • J.G. Power, S.P. Antipov, M.E. Conde, W. Gai, C.-J. Jing, W. Liu, E.E. Wisniewski, Z.M. Yusof
    ANL, Argonne, USA
 
  Funding: Work supported by High Energy Physics, Office of Science, US DOE
We report on the development of the diagnostic system for the ongoing upgrade to the Argonne Wakefield Accelerator (AWA) facility where the electron drive beam energy will be increased from 15 to 75 MeV. The facility will produce a wide dynamic range of drive bunch train formats ranging from a single microbunch of 100 pC to bunch trains of up to 32 bunches spaced by 769 ps with up to 100 nC per bunch. In addition to standard diagnostics, this drive bunch train format poses two challenges for the diagnostic system: (i) the close spacing of the drive bunches, 769 ps, makes resolving the individual pulses difficult and (ii) the dynamic range of the bunch charge varies by x1000. A critical parameter of the drive bunch train for the wakefield accelerator is the charge along the train. To measure this, we are planning to use a 15 GHz digital oscilloscope to read either a BPM or Bergoz FCT. To handle the large dynamic range of charge, the imaging system will make use of GigE Vision cameras and a distributed system of motorized lenses, with remote control of focus, zoom, and aperture, which are operated through terminal servers and RS232 controllers.
 
 
TUPPD069 Schottky-Enabled Photoemission and Dark Current Measurements - Toward an Alternate Approach to Fowler-Nordheim Plot Analysis 1563
 
  • E.E. Wisniewski, W. Gai, J.G. Power
    ANL, Argonne, USA
  • H. Chen, Y.-C. Du, Hua, J.F. Hua, W.-H. Huang, C.-X. Tang, L.X. Yan, Y. You
    TUB, Beijing, People's Republic of China
  • A. Grudiev, W. Wuensch
    CERN, Geneva, Switzerland
  • E.E. Wisniewski
    Illinois Institute of Technology, Chicago, Illinois, USA
 
  Field-emitted dark current, a major gradient-limiting factor in RF cavities, is usually analyzed via Fowler-Nordheim (FN) plots. Traditionally, field emission is attributed to geometrical perturbations on the bulk surface whose field enhancement factor (beta) and the emitting area (A) can be extracted from the FN plot. Field enhancement factors extracted in this way are typically much too high (1 to 2 orders of magnitude) to be explainable by either the geometric projection model applied to the measured surface roughness or by field enhancement factors extracted from Schottky-enabled photoemission measurements. We compare traditional analysis of FN plots to an alternate approach employing local work function variation. This is illustrated by comparative analysis of recent dark current and Schottky-enabled photoemission data taken at Tsinghua S-band RF gun. We conclude by describing a possible experimental plan for discrimination of variation of local work function vs. local field enhancement.  
 
TUPPD071 Development of Cesium Telluride Photocathodes for the AWA Accelerator Upgrade 1569
 
  • Z.M. Yusof, M.E. Conde, W. Gai
    ANL, Argonne, USA
  • L.K. Spentzouris, E.E. Wisniewski
    Illinois Institute of Technology, Chicago, Illinois, USA
 
  Funding: U.S. Department of Energy Office of Science under Contract No. DE-AC02-06CH11357.
Cesium telluride photocathodes have been fabricated for the Argonne Wakefield Accelerator (AWA) upgrade. The as-deposited photocathodes have consistently produced quantum efficiency values better than 10% with 254 nm light source and with variation of less than 5% over a circular area of 1.2 inches in diameter. We present various characterizations of the photocathode that have performed, including rejuvenation, lifetime, and performance in the L-band AWA photoinjector.
 
 
TUPPR040 Update on ILC Positron Source Study at ANL 1906
 
  • W. Liu, W. Gai
    ANL, Argonne, USA
 
  As the new ILC baseline has moved the positron production to the end of electron main linac, both the drive beam energy and beamline layouts have also been changed for the positron source. Now the drive beam energy will be varying from 150GeV to 250GeV and 500GeV (for TeV upgrade) as the colliding center of mass (CM) energy changes. Systematic studies on the performance of positron source under different running scenarios have been done at ANL and the results are presented in this paper.  
 
TUPPR041 Update on ILC Positron Source Start-to-End Simulation 1909
 
  • W. Liu, W. Gai
    ANL, Argonne, USA
 
  As a result of the changes in the new ILC base line, there are many changes in the positron source beamline layouts and thus a new lattice design is required. According to the changes in the ILC baseline, a new lattice design for the ILC positron source has been developed at ANL. In this paper, both the new ILC positron source beamline lattice and the corresponding start to end simulation results are presented.  
 
TUPPR042 On the Polarization Upgrade of ILC Undulator-based Positron Source 1912
 
  • W. Liu, W. Gai
    ANL, Argonne, USA
  • S. Riemann
    DESY, Hamburg, Germany
  • A. Ushakov
    University of Hamburg, Hamburg, Germany
 
  The current nominal polarization for ILC undulator based positron source is 30% without photon collimators. In order to improve the effective luminosity, an upgrade of positron source with higher polarization is required. Some studies on the upgrade options have been done at both DESY and ANL, and the results are presented in this paper.  
 
TUPPR048 Short RF Pulse Linear Collider 1924
 
  • C.-J. Jing, S.P. Antipov, A. Kanareykin, P. Schoessow
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • M.E. Conde, W. Gai, J.G. Power
    ANL, Argonne, USA
 
  Funding: DOE SBIR program under Contractor #DE-SC0004320
In general, a high gradient is desirable for future linear collider designs because it can reduce the total linac length. More importantly, the efficiency and the cost to sustain the high gradient should also be considered in the optimization process of an overall design. In this article, we explore a parametric territory of short rf pulse, high group velocity, high frequency, and high gradient, etc., that may lead to an affordable high energy linear collider in the future.
 
 
WEPPD076 A Fast Kicker for a Staged Dielectric Two-beam Wakefield Accelerator 2702
 
  • J.G. Power, M.E. Conde, W. Gai
    ANL, Argonne, USA
  • C.-J. Jing
    Euclid TechLabs, LLC, Solon, Ohio, USA
 
  Funding: Work supported by DoE, Office of HEP.
An experimental program to demonstrate staging in a dielectric two-beam wakefield accelerator (dielectric TBA) is being planned at the Argonne Wakefield Accelerator (AWA) facility. We are planning an experiment that both fits in the AWA tunnel and mimics conditions similar to the recently presented conceptual design of a linear collider based on the dielectric TBA. This conceptual design is based on a new parameter space of the TBA scheme utilizing an ultra-short (~20ns) rf pulse in a dielectric TBA. The decelerating structures are driven by a series of drive microbunch trains that are 20 ns in duration and separated by 100 ns. This means that the fast kicker must have an extremely quick risetime as well as become stable within about 50 ns. In this paper, we consider designs for a fast kicker based on RF deflecting cavities and stripline kickers.
 
 
WEPPD077 Generation of Picosecond Electron-bunch Trains with Variable Spacing Using a Multi-pulse Photocathode Laser 2705
 
  • P. Piot
    Fermilab, Batavia, USA
  • M.E. Conde, W. Gai, C.-J. Jing, R. Konecny, W. Liu, J.G. Power, Z.M. Yusof
    ANL, Argonne, USA
  • D. Mihalcea, P. Piot, M.M. Rihaoui
    Northern Illinois University, DeKalb, Illinois, USA
 
  Funding: Work supported by DOE awards FG-02-08ER41532 and DE-AC02-06CH11357.
We demonstrate the generation of a train of electron bunches with variable spacing at the Argonne Wakefield Accelerator. The photocathode ultraviolet laser pulse consists of a train of four pulses produced via polarization splitting using two alpha-BBO crystals. The photoemitted electron bunches are then manipulated in a horizontally-bending dogleg with variable longitudinal dispersion. A downstream vertically-deflecting cavity is then used to diagnose the temporal profile of the electron beam. The generation of a train composed of four bunches with tunable spacing is demonstrated. Such train of bunch could have application to, e.g., the resonant excitation of wakefield in dielectric-lined waveguides.
 
 
WEPPP025 A Test-bed for Future Linear Collider Technology: Argonne Wakefield Accelerator Facility (AWA) 2778
 
  • M.E. Conde, D.S. Doran, W. Gai, R. Konecny, W. Liu, J.G. Power, Z.M. Yusof
    ANL, Argonne, USA
  • S.P. Antipov, C.-J. Jing
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • E.E. Wisniewski
    Illinois Institute of Technology, Chicago, Illinois, USA
 
  Funding: Work supported by the U.S. Department of Energy under contract No. DE-AC02-06CH11357.
Research at the AWA Facility has been focused on the development of electron beam driven wakefield structures. Accelerating gradients of up to 100 MV/m have been excited in dielectric loaded cylindrical structures operating in the microwave range of frequencies. Several upgrades, presently underway, will enable the facility to explore higher accelerating gradients, and also be able to generate longer RF pulses of higher intensity. The upgraded 75 MeV drive beam will consist of bunch trains of up to 32 bunches spaced by 0.77 ns with up to 100 nC per bunch. The RF pulses generated by the drive bunches are expected to reach GW power levels, establishing accelerating gradients of hundreds of MV/m.
 
 
WEPPP041 Wakefield Breakdown Test of a Diamond-loaded Accelerating Structure at the AWA 2813
 
  • S.P. Antipov, J.E. Butler, C.-J. Jing, A. Kanareykin, P. Schoessow, S.S. Zuo
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • S. Baryshev, M.E. Conde, D.S. Doran, W. Gai, R. Konecny, J.G. Power, Z.M. Yusof
    ANL, Argonne, USA
 
  Funding: DOE SBIR
Diamond has been proposed as a dielectric material for dielectric loaded accelerating (DLA) structures. It has a very low microwave loss tangent, the highest available thermoconductive coefficient and high RF breakdown field. In this paper we report results from a wakefield breakdown test of diamond-loaded rectangular accelerating structure. The high charge beam from the AWA linac (~70 nC, σz = 2.5mm) will be passed through a rectangular diamond - loaded resonator and induce an intense wakefield. A groove is cut on the diamond to enhance the field. Electric fields up to 0.5 GV/m will be present on the diamond surface to attempt to initiate breakdown. A surface analysis of the diamond is be performed before and after the beam test.
 
 
WEPPP042 Experimental Demonstration of Wakefield Effects in a 250 GHz Planar Diamond Accelerating Structure 2816
 
  • S.P. Antipov, J.E. Butler, C.-J. Jing, A. Kanareykin, P. Schoessow, S.S. Zuo
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • M.G. Fedurin, K. Kusche, V. Yakimenko
    BNL, Upton, Long Island, New York, USA
  • W. Gai
    ANL, Argonne, USA
 
  Funding: DOE SBIR
We have directly measured the mm-wave wake fields induced by subpicosecond, intense relativistic electron bunches in a diamond loaded accelerating structure via the dielectric wake-field acceleration mechanism. Fields produced by a first, drive, beam were used to accelerate a second, witness, electron bunch which followed the driving bunch at an adjustable distance. The energy gain of the witness bunch as a function of its separation from the drive bunch is a direct measurement of the wake potential. We also present wakefield mapping results for THz quartz structures. In this case decelerating wake inside the bunch is inferred from the drive beam energy modulation.
 
 
THPPC031 Commissioning of a 1.3-GHz Deflecting Cavity for Phase-Space Exchange at the Argonne Wakefield Accelerator 3350
 
  • P. Piot
    Fermilab, Batavia, USA
  • M.E. Conde, W. Gai, C.-J. Jing, R. Konecny, W. Liu, J.G. Power, Z.M. Yusof
    ANL, Argonne, USA
  • D. Mihalcea, M.M. Rihaoui
    Northern Illinois University, DeKalb, Illinois, USA
 
  Funding: Work supported by DOE awards FG-02-08ER41532 and DE-AC02-06CH11357.
A 1/2-1-1/2 cell normal-conducting 1.3-GHz deflecting cavity was recently installed at the Argonne Wakefield Accelerator. The cavity will soon be included in a transverse-to-longitudinal phase space exchanger that will eventually be used to shaped the current profile of AWA electron bunches in support of dielectric wakefield experimentS with enhanced transformer ratio. In this paper we report on the initial commissioning of the deflecting cavity including rf-conditioning and beam-based measurement of the deflecting strength.
 
 
THPPC074 High Frequency High Power RF Generation using a Relativistic Electron Beam 3458
 
  • C.-J. Jing, S.P. Antipov, A. Kanareykin, P. Schoessow
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • H. Chen, Y. Yang
    TUB, Beijing, People's Republic of China
  • M.E. Conde, W. Gai, J.G. Power
    ANL, Argonne, USA
 
  High frequency, high power rf sources are required for many applications. Benefiting from the ~10 GW beam power provided by the high current linac at the Argonne Wakefield Accelerator facility, we propose to develop a series of high power rf sources based on the extraction of coherent Cherenkov radiation from the relativistic electron beam. The frequencies cover from C-band up to W-band with different structures. Simulations show that ~1 GW 20 ns rf pulse can be generated for an 11.7 GHz structure, ~400 MW for a 26 GHz structure, and ~14 MW for a 91 GHz structure.