| Paper |
Title |
Page |
| THPMN099 |
Plans for a 750 MeV Electron Beam Test Facility at Fermilab
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2942 |
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- M. Church, S. Nagaitsev, P. Piot
Fermilab, Batavia, Illinois
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A 750 MeV electron beam test facility at Fermilab is in the planning and early construction phase. An existing building is being converted for this facility. The photoinjector currently in use at the Fermilab NICADD Photoinjector Laboratory (FNPL) will be moved to the new facility and upgraded to serve as an injector for a beam acceleration section consisting of 3 Tesla or ILC-type cryomodules. A low energy off-axis beam will be constructed to test ILC crab cavity designs and provide opportunities for other tests. Downstream beamlines will consist of a diagnostic section, a beam test area for additional beam experiments, and a high power beam dump. The initial program for this facility will concentrate on testing ILC-type cryomodules and RF control with full ILC beam intensity. A future building expansion will open up further possibiliities for beam physics and beam technology experiments.
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| WEOAKI02 |
Observations of Underdense Plasma Lens Focusing of Relativistic Electron Beams
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1907 |
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- M. C. Thompson, M. C. Thompson
LLNL, Livermore, California
- H. Badakov, J. B. Rosenzweig, R. Tikhoplav, G. Travish
UCLA, Los Angeles, California
- R. P. Fliller, G. M. Kazakevich, J. K. Santucci
Fermilab, Batavia, Illinois
- J. L. Li
Rochester University, Rochester, New York
- P. Piot
Northern Illinois University, DeKalb, Illinois
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Funding: This work was performed under the auspices of the US Department of Energy under Contract No. DE-FG03-92ER40693 and W-7405-ENG-48.
Focusing of a 15 MeV, 19 nC electron bunch by an underdense plasma lens operated just beyond the threshold of the underdense condition has been demonstrated in experiments at the Fermilab NICADD Photoinjector Laboratory (FNPL). The strong 1.9 cm focal-length plasma-lens focused both transverse directions simultaneously and reduced the minimum area of the beam spot by a factor of 23. Analysis of the beam-envelope evolution observed near the beam waist shows that the spherical aberrations of this underdense lens are lower than those of an overdense plasma lens, as predicted by theory. Correlations between the beam charge and the properties of the beam focus corroborate this conclusion. Time resolved measurements of the focused electron bunch are also reported and all results are compared to simulations.
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Slides
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| THPMS010 |
Polarized Pulsed Beam Source for Electron Microscopy
|
3011 |
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- N. Vinogradov, C. L. Bohn, P. Piot
Northern Illinois University, DeKalb, Illinois
- J. W. Lewellen, J. Noonan
ANL, Argonne, Illinois
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A novel source of polarized pulsed electron beam is discussed. Unlike conventional devices based either on a thermionic cathodes or field-emission needle cathodes, in this source the electrons are produced by a laser beam hitting the cathode surface. Using a combination of gallium arsenide (GaAs) planar cathode and a suitable laser one can obtain a polarized picosecond electron bunch. Numerical simulations of the electron dynamics in the optimized cathode-anode geometry have shown that the beam with initial transverse size of a few mm can be focused down to 1 mm RMS at a distance of about 4 cm from the cathode. The suggested source can be installed instead of a tungsten filament source in an existing electron microscope with no modification of any column elements. The main advantages of this approach are that the beam can be easily pulsed, the beam is polarized which makes it an effective probe of some magnetic phenomena, and the laser can be used to provide larger beam intensity. The design of the source and subsequent fabrication has been completed. The paper presents numerical studies, conceptual design of the device, and results of beam measurements.
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| THPAN094 |
Design Study of a Transverse-to-Longitudinal Emittance Exchange Proof-of-principle Experiment
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3441 |
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- Y.-E. S. Sun, K.-J. Kim, J. G. Power
ANL, Argonne, Illinois
- P. Piot, M. M. Rihaoui
Northern Illinois University, DeKalb, Illinois
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Funding: Dr. Sun's work is supported by U. S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.
Transverse-to-longitudinal emittance exchange can be achieved through certain arrangements of dipole magnets and dipole mode rf cavity. Theory on such schemes has been developed in the past several years. In this paper we report our numerical simulations on the emittance exchange using particle tracking codes. Photoelectron beams with energy less than 20 MeV are used, as our purpose of simulations is to study the feasibility of performing such emittance exchange at existing facilities of beam energy at this level. Parametric studies of the dipole magnets and cavity strengths, as well as initial beam parameters, are presented.
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| FRPMN117 |
Pepper-pot Based Emittance Measurements of the AWA Photoinjector
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4393 |
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- 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
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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.
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| FRPMS035 |
Vector Diffraction Theory and Coherent Transition Radiation Interferometry in Electron Linacs
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4015 |
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- T. J. Maxwell, C. L. Bohn, D. Mihalcea, P. Piot
Northern Illinois University, DeKalb, Illinois
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Funding: Work supported by US. Department of Energy, under Contract No. DE-FG02-06ER41435 with Northern Illinois University
Electrons impinging on a thin metallic foil are seen to deliver small bursts of transition radiation (TR) as they cross the boundary from one medium to the next. A popular diagnostic application is found for compact electron bunches. In this case they will emit radiation more or less coherently with an N-squared enhancement of the intensity on wavelengths comparable to the bunch size, generating coherent transition radiation (CTR). Several detailed analytical descriptions have been proposed for describing the resulting spectral distribution, often making different simplifying assumptions. Given that bunches tenths of millimeters long can generate measurable spectra into the millimeter range, concern may arise as to weak diffraction effects produced by optical interference devices containing elements with dimensions in the centimeter range. The work presented here is a report on an upcoming graduate thesis exploring these effects as they apply to the Fermilab/NICADD photoinjector laboratory using a minimal C++ code that implements the methods of virtual quanta and vector diffraction theory.
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| FRPMS037 |
Impact of Transverse Irregularities at the Photocathode on High-Charge Electron Bunches
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4027 |
| |
- M. M. Rihaoui, C. L. Bohn, P. Piot
Northern Illinois University, DeKalb, Illinois
- J. G. Power
ANL, Argonne, Illinois
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Electron beam properties in photoinjectors are strongly dependent on the initial conditions, e.g., non-uniformities in the drive-laser pulse and/or the photocathode surface. We explore the impact of well-defined transverse perturbation modes on the evolution of the electron beam phase space, and paying special attention to how certain types of perturbations mix. Numerical simulations performed with IMPACT-T (both the standard version and a new wavelet-based version) are presented along with experimental results aimed at validating the simulation codes. The experiments are conducted at the Argonne Wakefield Accelerator facility.
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