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Yusof, Z. M.

Paper Title Page
THPMN085 Proposed Dark Current Studies at the Argonne Wakefield Accelerator Facility 2904
 
  • S. P. Antipov, M. E. Conde, W. Gai, J. G. Power, Z. M. Yusof
    ANL, Argonne, Illinois
  • V. A. Dolgashev
    SLAC, Menlo Park, California
  • L. K. Spentzouris
    Illinois Institute of Technology, Chicago, Illinois
 
  Funding: US Department of Energy

A study of breakdown mechanism has been initiated at the Argonne Wakefield Accelerator Facility (AWA). Breakdown may include several factors such as local field enhancement, explosive electron emission, Ohmic heating, tensile stress produced by electric field, and others. The AWA is building a dedicated facility to test various models for breakdown mechanisms and to determine the roles of different factors in the breakdown. An imaging system is being put together to identify single emitters on the cathode surface. This will allow us to study dark current properties in the gun. We also plan to trigger breakdown events with a high-powered laser at various wavelengths (IR to UV). Another experimental idea follows from the recent work on a Schottky-enabled photoemission in an RF photoinjector that allows us to determine in situ the field enhancement factor on a cathode surface. Monitoring the field enhancement factor before and after can shed some light on a modification of metal surface after the breakdown.

 
THPMN086 Metamaterial-loaded Waveguides for Accelerator Applications 2906
 
  • S. P. Antipov, M. E. Conde, W. Gai, R. Konecny, W. Liu, J. G. Power, Z. M. Yusof
    ANL, Argonne, Illinois
  • L. K. Spentzouris
    Illinois Institute of Technology, Chicago, Illinois
 
  Funding: US Department of Energy National Science Foundation grant # 0237162

Metamaterials (MTM) are artificial periodic structures made of small elements and designed to obtain specific electromagnetic properties. As long as the periodicity and the size of the elements are much smaller than the wavelength of interest, an artificial structure can be described by a permittivity and permeability, just like natural materials. Metamaterials can be customized to have the permittivity and permeability desired for a particular application. Waveguides loaded with metamaterials are of interest because the metamaterials can change the dispersion relation of the waveguide significantly. Slow backward waves, for example, can be produced in a LHM-loaded waveguide without corrugations. In this paper we present theoretical studies and computer modeling of waveguides loaded with 2D anisotropic metamaterials, including the dispersion relation for a MTM-loaded waveguide. The dispersion relation of a MTM-loaded waveguide has several interesting frequency bands which are described. It is shown theoretically that dipole mode suppression may be possible. Therefore, metamaterials can be used to suppress wakefields in accelerating structures.

 
THPMN088 C-Band High Power RF Generation and Extraction Using a Dielectric Loaded Waveguide 2912
 
  • F. Gao, M. E. Conde, W. Gai, R. Konecny, W. Liu, J. G. Power, Z. M. Yusof
    ANL, Argonne, Illinois
  • C.-J. Jing
    Euclid TechLabs, LLC, Solon, Ohio
  • T. Wong
    Illinois Institute of Technology, Chicago, Illinois
 
  Funding: Department of Energy

We report on the fabrication, simulation, and high-power testing of a C-band RF power extractor recently conducted at the Argonne Wakefield Accelerator (AWA) facility. Dielectric loaded accelerating (DLA) structures can be used for high-power RF generation [*,**] when a high-current electron beam passes through a DLA structure and loses energy into the modes of the structure due to self-wakefields. The AWA generates high charge (up to 100nC), short bunch length (1.5mm~2.5mm) electron beams, which is ideal for high-power RF generation. The generated RF power can be subsequently extracted with a properly designed extraction coupler in order to accelerate a second beam, or for other high power purposes. In this paper, the detailed design of a 7.8 GHz DLA power extractor, MAFIA simulations, and results of the high-power test are presented. Simulation predictions of an 79 MW, 2.2 ns long RF pulse (generated by a single 100 nC electron bunch) and a longer RF pulse of the same power (obtained from a 35 nC periodic bunch train) will be compared to experimental results.

* W. Gai, et al, Experimental Demonstration of Two Beam Acceleration Using Dielectric Step-up Transformer, PAC01, pp.1880-1882.** D. Yu, et al, 21GHz Ceramic RF Power Extractor, AAC02, pp.484-505.

 
THPMS074 High Transformer Ratios in Collinear Wakefield Accelerators 3154
 
  • C.-J. Jing, A. Kanareykin, P. Schoessow
    Euclid TechLabs, LLC, Solon, Ohio
  • M. E. Conde, W. Gai, J. G. Power, Z. M. Yusof
    ANL, Argonne, Illinois
 
  Funding: DOE SBIR Phase II, DE-FG02-02ER83418.

Based on our previous experiment that successfully demonstrated wakefield transformer ratio enhancement in a 13.625 GHz dielectric-loaded collinear wakefield accelerator using the ramped bunch train technique, we present here a redesigned experimental scheme for even higher enhancement of the efficiency of this accelerator. Design of a collinear wakefield device with a transformer ratio R>>2, is presented. Using a ramped bunch train (RBT) rather than a single drive bunch, the enhanced transformer ratio (ETR) technique is able to increase the transformer ratio R above the ordinary limit of 2. To match the wavelength of the fundamental mode of the wakefield with the bunch length (σz=2 mm) of the new Argonne Wakefield Accelerator (AWA) drive gun, where the experiment will be performed, a 26.625 GHz dielectric based accelerating structure is required. This transformer ratio enhancement technique based on our dielectric-loaded waveguide design will result in a compact, high efficiency accelerating structure for future wakefield accelerators.

 
THPMS075 High Power Testing of a Fused Quartz-based Dielectric-loaded Accelerating Structure 3157
 
  • C.-J. Jing
    Euclid TechLabs, LLC, Solon, Ohio
  • V. A. Dolgashev, S. G. Tantawi
    SLAC, Menlo Park, California
  • W. Gai, R. Konecny, J. G. Power, Z. M. Yusof
    ANL, Argonne, Illinois
  • S. H. Gold
    NRL, Washington, DC
  • A. K. Kinkead
    LET
 
  We report on the most recent results from a series of high power tests being carried out on RF-driven dielectric-loaded accelerating (DLA) structures. The purpose of these tests is to determine the viability of the DLA as a traveling-wave accelerator and is a collaborative effort between Argonne National Laboratory (ANL), Naval Research Laboratory (NRL), and Stanford Linear Accelerator Center (SLAC). In this paper, we report on the recent high power tests of a fused quartz-based DLA structure that was carried out at incident powers of up to 12 MW at NRL and 37 MW at SLAC. We report experimental details of the RF conditioning process and make comparison of our multipactor model to the experiment, including tests of geometrical scaling laws and the time evolution of multipactor. Finally, we discuss future plans for the program including a planned test of new quartz-based DLA with a different geometry to both reach higher accelerating gradients and to continue the parametric study of multipactor.  
FRPMN117 Pepper-pot Based Emittance Measurements of the AWA Photoinjector 4393
 
  • J. G. Power, M. E. Conde, W. Gai, F. Gao, R. Konecny, W. Liu, Z. M. Yusof
    ANL, Argonne, Illinois
  • P. Piot, M. M. Rihaoui
    Northern Illinois University, DeKalb, Illinois
 
  The Argonne Wakefield Accelerator (AWA) RF photocathode gun is a 1.5 cell, L-band, RF photocathode gun operating at 80 MV/m, with an emittance compensating solenoid, and a magnesium photocathode and generates an 8 MeV, 1 nC - 100 nC beam. In this paper, we report on a parametric set of measurements to characterize the transverse trace space of the 1 nC electron beam directly out of the gun. The entire experiment is simulated with PARMELA, from the photocathode, through the pepper pot, and to the imaging screen. The transverse trace-space is sampled with a 2-D pepper pot which allows for simultaneous, single-shot measurements, of both the x and y distributions. A series of pepper pots were available during the experiment to increase the dynamic range of emittance measurements. Realistic particle distributions are used for the simulations and are derived from actual laser profiles, which were captured from a virtual cathode and generated with MATLAB-based particle generator. We report both the second moment (emittance) and the detailed phase space distribution over a gun launch phase range of approximately 50 degrees.