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| TPAE016 | The Argonne Wakefield Accelerator Facility: Status and Recent Activities | 1485 |
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Funding: This work is supported by the U.S. Department of Energy, under contract No. W-31-109-ENG-38. The Argonne Wakefield Accelerator Facility (AWA) is dedicated to the study of electron beam physics and the development of accelerating structures based on electron beam driven wakefields. In order to carry out these studies, the facility employs a photocathode RF gun capable of generating electron beams with high bunch charges (up to 100 nC) and short bunch lengths. This high intensity beam is used to excite wakefields in the structures under investigation. The wakefield structures presently under development are dielectric loaded cylindrical waveguides with operating frequencies of 7.8 or 15.6 GHz. The facility is also used to investigate the generation and propagation of high brightness electron beams. Presently under investigation, is the use of photons with energies lower than the work function of the cathode surface (Schottky-enabled photoemission), aimed at generating electron beams with low thermal emittance. Novel electron beam diagnostics are also developed and tested at the facility. The AWA electron beam is also used in laboratory-based astrophysics experiments; namely, measurements of microwave Cherenkov radiation and fluorescence of air. We report on the current status of the facility and present recent results. |
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| TPAE017 | Progress on High Power Tests of Dielectric-Loaded Accelerating Structures | 1566 |
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Funding: This work was supported by the U.S. Dept of Energy, High Energy Physics Division and Office of Naval Research. This paper presents a progress report on a series of high-power rf experiments that were carried out to evaluate the potential of the Dielectric-Loaded Accelerating (DLA) structure for high-gradient accelerator operation. Since the last PAC meeting in 2003, we have tested DLA structures loaded with two different ceramic materials: Alumina (Al2O3) and MCT (MgxCa1-xTiO3). The alumina-based DLA experiments have concentrated on the effects of multipactor in the structures under high-power operation, and its suppression using TiN coatings, while the MCT experiments have investigated the dielectric joint breakdown observed in the structures due to local field enhancement. In both cases, physical models have been set up, and the potential engineering solutions are being investigated. |
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| TPAE018 | 34.272 GHz Multilayered Dielectric-Loaded Accelerating Structure | 1592 |
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| A scheme of multilayered structure design of 34.272 GHz with alternating dielectric of 38 and 9.7 is presented. The multilayer structure employs the Bragg Fiber concepts where the dielectric layers are used to create multiple reflections in order to confine the accelerating fields, thus greatly reducing the power loss of from external metal wall. The structure will operate at TM03 mode instead of normal TM01 mode. Numerical examples for the 2- and 4-layers 34.272 GHz multilayered structures are presented with detailed analysis of TM (acceleration) modes and HEM (parasitic) modes. We found that the power attenuation of the proposed structure can be lowered from ~ 20 dB/m for a single layer structure to ~ 6 dB/m for 2 -4 layered structure in at 34.272 GHz. We will also present a coupler design for the multilayered dielectric-loaded accelerating structure, which has capability of mode selection and high efficient RF transmission. | ||
| TPAE060 | Planned Enhanced Wakefield Transformer Ratio Experiment at Argonne Wakefield Accelerator | 3487 |
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Funding: U.S. Department of Energy. In this paper, we present a preliminary experimental study of a wakefield accelerating scheme that uses a carefully spaced and current ramped electron pulse train to produce wakefields that increases the transformer ratio much higher than 2. A dielectric structure was designed and fabricated to operate at 13.625 GHz with dielectric constant of 15.7. The structure will be initially excited by two beams with first and second beam charge ratio of 1:3. The expected transformer ratio is 3 and the setup can be easily extend to 4 pulses which leads to a transformer ratio of more than 6. The dielectric structure cold test results show the tube is within the specification. A set of laser splitters was also tested to produce ramped bunch train of 2 - 4 pulses. Overall design of the experiment and initial results will be presented. |
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| TPAE061 | Experimental Investigation of an X-Band Tunable Dielectric Accelerating Structure | 3529 |
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Funding: U.S. Department of Energy. Experimental study of a new scheme to tune the resonant frequency for dielectric based accelerating structure (driven either by the wakefield of a beam or an external rf source) is underway. The structure consists of a single layer of conventional dielectric surrounded by a very thin layer of ferroelectric material situated on the outside. Carefully designed electrodes are attached to a thin layer of ferroelectric material. A DC bias can be applied to the electrodes to change the permittivity of the ferroelectric layer and therefore, the dielectric overall resonant frequency can be tuned. In this paper, we present the test results for an 11.424 GHz rectangular DLA prototype structure that the ferroelectric material's dielectric constant of 500 and show that a frequency tuning range of 2% can be achieved. If successful, this scheme would compensate for structure errors caused by ceramic waveguide machining tolerances and dielectric constant heterogeneity. |
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| TPAE065 | Development of a 20-MeV Dielectric-Loaded Accelerator Test Facility | 3673 |
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Funding: Work supported by DOE and ONR. This paper will describe a joint project by the Naval Research Laboratory (NRL) and Argonne National Laboratory (ANL), in collaboration with the Stanford Linear Accelerator Center (SLAC), to develop a dielectric-loaded accelerator (DLA) test facility powered by the high-power 11.424-GHz magnicon that was developed by NRL and Omega-P, Inc. The magnicon can presently produce 25 MW of output power in a 250-ns pulse at 10 Hz, and efforts are in progress to increase this to 50 MW.* The facility will include a 5-MeV electron injector being developed by the Accelerator Laboratory of Tsinghua University in Beijing, China. The DLA test structures are being developed by ANL, and some have undergone testing at NRL at gradients up to ~8 MV/m.** SLAC is developing a means to combine the two magnicon output arms, and to drive an injector and accelerator with separate control of the power ratio and relative phase. The installation and testing of the first dielectric-loaded test accelerator, including injector, DLA structure, and spectrometer, should take place within the next year. The initial goal is to produce a compact 20-MeV dielectric-loaded test accelerator. *O. A. Nezhevenko et al., Proc. PAC 2003, p. 1128.**S. H. Gold et al., AIP Conf. Proc. 691, p. 282. |
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| TPAT058 | Calculation of Electron Beam Potential Energy from RF Photocathode Gun | 3441 |
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Funding: U.S. Department of Energy. In this paper, we consider the contribution of potential energy to beam dynamics as simulated by PARMELA at low energies (10 - 30MeV). We have developed a routine to calculate the potential energy of the relativistic electron beam using the static coulomb potential in the rest frame (first order approximation as in PARMELA). We found that the potential energy contribution to the beam dynamics could be very significant, particularly with high charge beams generated by an RF photocathode gun. Our results show that when the potential energy is counted correctly and added to the kinetic energy from PARMELA, the total energy is conserved. Simulation results of potential and kinetic energies for short beams (~1 mm) at various charges (1 - 100 nC) generated by a high current RF photocathode gun are presented. |
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| WPAP034 | Positron Emulator for Commissioning ILC Positron Source | 2321 |
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Funding: U.S. DOE. It is apparent that the gamma-ray based positron source components including positron linac and damping rings for ILC can not be easily commissioned until the electron beam is fully conditioned at high energies (> 150 GeV). In this paper, we discuss a scheme that could use a short and energetic electron beam scattered through a set of carefully selected targets to simulate certain behaviors of the positron beam, such as beam emittance and energy spread. The basic idea is to make the phase space distribution of the scattered electron beam to reflect certain aspects of the positron beam distributions. Subsequently, the positron source elements such as capture optics, linacs and even damping ring could be effectively commissioned before ILC colliding electron beam is ready. The simulation results using EGS4 for beam scattering and PARMELA for beam dynamics are presented. |
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| WPAP036 | Determination of the Field Enhancement Factor on Photocathode Surface Via the Schottky Effect | 2425 |
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Funding: U.S. Department of Energy. Using photons with energy that is less than the work function, we employ the Schottky effect to determine the field enhancement factor on the surface of a Mg photocathode. The Schottky effect is manifested via a shift in the threshold for photoemission as the amplitude of the RF in the photoinjector gun is varied. From the threshold condition, we can directly determine the field enhancement factor on the cathode surface. This is a viable technique to obtain the field enhancement factor of surfaces of other materials such as Nb and Cu. |
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| ROPC006 | Commissioning of Fermilab's Electron Cooling System for 8-GeV Antiprotons | 540 |
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| A 4.3-MeV electron cooling system has been installed at Fermilab in the Recycler antiproton storage ring and is being currently commissioned. The cooling system is designed to assist accumulation of 8.9-GeV/c antiprotons for the Tevatron collider operations. This paper will report on the progress of the electron beam commissioning effort as well as on detailed plans of demonstrating the cooling of antiprotons. |