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| MOPAS032 | Advanced Accelerator Control and Instrumentation Modules based on FPGA | 506 |
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Funding: Work supported by U. S. DOE Office of Science, Office of High Energy Physics, under grant DE-FG02-06ER84486. Field Programmable Gate Arrays (FPGAs) offer a powerful alternative to ASICs or general purpose processors in accelerator control applications. Software development for these devices can be awkward and time consuming, however, when using low level hardware design languages. To facilitate the use of FPGAs in control systems we are developing a library of software tools based on ImpulseC, a high level subset of the C language specifically designed for FPGA programming. Development and testing of the software will be performed on a Xilinx Virtex-4 FPGA demo board. We will present timing benchmarks for common control functions (PID feedback loops, FIR and Kalman filters) and present plans for the development of a controller for the Argonne Wakefield Accelerator high current photoinjector based on this work. |
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| THPMN085 | Proposed Dark Current Studies at the Argonne Wakefield Accelerator Facility | 2904 |
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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. |
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| THPMN086 | Metamaterial-loaded Waveguides for Accelerator Applications | 2906 |
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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. |
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| THPMN088 | C-Band High Power RF Generation and Extraction Using a Dielectric Loaded Waveguide | 2912 |
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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. |
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| THPMS073 | Progress towards a Gap Free Dielectric-Loaded Accelerator | 3151 |
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One of the major concerns in the development of Dielectric-Loaded Accelerating (DLA) structures is the destructive breakdown at dielectric joints caused by a local electric field enhancement induced by the discontinuity of the dielectric constant on the surface of the joint gap. Our previous X-band traveling wave DLA structure design*, for example, incorporated two separate impedance matching sections with at least two dielectric joints. In this paper, we present a new design to avoid this problem. This scheme is based on a coaxial type coupler which is able to implement mode conversion and impedance matching at the same time and therefore to eliminate joint gap induced breakdown. The new structure is under construction; bench test results will be presented
* C. Jing, W. Gai, J. Power, R. Konecny, S. Gold, W. Liu and A. Kinkead, IEEE, Trans. PS, vol.33 No.4, Aug. 2005, pp.1155-1160. |
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| THPMS074 | High Transformer Ratios in Collinear Wakefield Accelerators | 3154 |
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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. |
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| THPMS075 | High Power Testing of a Fused Quartz-based Dielectric-loaded Accelerating Structure | 3157 |
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| 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. | ||
| THPMS078 | Status of the Microwave PASER Experiment | 3166 |
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Funding: Work supported by US Department of Energy The PASER is a new method for particle acceleration, in which energy from an active medium is transferred to a charged particle beam. The effect is similar to the action of a maser or laser with the stimulated emission of radiation being produced by the virtual photons in the electromagnetic field of the beam. We are developing a demonstration PASER device operating at X-band, based on the availability of a new class of active materials that exhibit photoinduced electron spin polarization. We will report on the status of active material development and measurements, numerical simulations, and preparations for microwave PASER experiments at the Argonne Wakefield Accelerator facility. |
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| THPMS096 | Development of a Dielectric-Loaded Test Accelerator | 3211 |
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Funding: Work supported by DoE and ONR.
A joint project is underway by the Naval Research Laboratory (NRL) and Argonne National Laboratory (ANL), in collaboration with the Stanford Linear Accelerator Center (SLAC), to develop a compact X-band accelerator for testing dielectric-loaded accelerator (DLA) structures.* The accelerator will use a 5-MeV injector previously developed by the Tsinghua University in Beijing, China, and will accommodate test structures up to 0.5 m in length. Both the injector and the structures will be powered by an 11.4-GHz magnicon amplifier that can produce 25 MW, 200-ns output pulses at up to 10 Hz. The injector will require ~5 MW of rf power, leaving ~20 MW to power the test structures. This paper will present a progress report on the construction and commissioning of the test accelerator, which will be located in a concrete bunker in the Magnicon Facility at NRL.
* S. H. Gold et al., Proc. PAC 2005. |
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| THPAN094 | Design Study of a Transverse-to-Longitudinal Emittance Exchange Proof-of-principle Experiment | 3441 |
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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 | 4393 |
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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. | ||
| FRPMS011 | Design of an Electro-Optical Sampling Experiment at the AWA Facility | 3901 |
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Funding: Supported by US DOE The free space electro-optical (EO) sampling technique is a powerful tool for analyzing the longitudinal charge density of an ultrashort e-beam. In this paper, we present
* Yuelin Li, Appl. Phys. Lett. 88, 251108, 2006 |
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| FRPMS034 | Optical Diffraction-Dielectric Foil Radiation Interferometry Diagnostic for Low Energy Electron Beams | 4012 |
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Funding: ONR and the DOD/Joint Technology Office
We have developed a new optical diffraction radiation (ODR) - dielectric foil radiation interferometer to measure the divergence of the low energy (8 - 14 MeV) ANL - Advanced Wakefield Accelerator electron beam. The interferometer employs an electro-formed micromesh first foil, which overcomes the inherent scattering limitation in the solid first foil of a conventional OTR interferometer, and an optically transparent second foil. The interference of forward directed ODR from the mesh and optical radiation from the dielectric foil is observed in transmission. This geometry allows a small gap between the foils (1 - 2 mm), which is required to observe fringes from two foils at low beam energies. Our measurements indicate that a single Gaussian distribution is sufficient to fit the data.
correspondance email: shkvar@umd.edu |
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| FRPMS037 | Impact of Transverse Irregularities at the Photocathode on High-Charge Electron Bunches | 4027 |
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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. | ||
| FRPMS094 | Beam Breakup Instabilities in Dielectric Structures | 4300 |
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Funding: This research is supported by the US Department of Energy We report on the experimental and numerical investigation of beam breakup (BBU) effects in dielectric structures resulting from parasitic wakefields. The experimental program focuses on measurements of BBU in a number of wakefield devices: (a) a 26 GHz power extraction structure; (b) a high gradient dielectric wakefield accelerator; (c) a wakefield structure driven by a high current ramped bunch train for multibunch BBU studies. New beam diagnostics will provide methods for studying parasitic wakefields that are currently unavailable at the AWA facility. The numerical part of this research is based on a particle-Green's function based beam breakup code we are developing that allows rapid, efficient simulation of beam breakup effects in advanced linear accelerators. The goal of this work is to be able to compare the accurate numerical results obtained from the new BBU code with the results of the detailed experimental measurements. An external focusing system for the control of the beam in the presence of strong transverse wakefields is considered. |