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| WEOAPA01 |
Demonstration of Energy Gain Larger than 10GeV in a Plasma Wakefield Accelerator
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- P. Muggli, S. Deng, T.C. Katsouleas, E. Oz
USC, Los Angeles, California
- D. Auerbach, C.E. Clayton, C. Huang, D.K. Johnson, C. Joshi, W. Lu, K.A. Marsh, W.B. Mori, M. Zhou
UCLA, Los Angeles, California
- I. Blumenfeld, F.-J. Decker, P. Emma, M.J. Hogan, R. Ischebeck, R.H. Iverson, N.A. Kirby, P. Krejcik, R. Siemann, D.R. Walz
SLAC, Menlo Park, California
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We have recently demonstrating the excitation of accelerating gradients as large as 30 GV/m* using the ultra-short, 28.5 GeV electron bunches now available at the Stanford Linear Accelerator Center. As a result, the electrons in the back of the bunch gained about 3 GeV over the 10 cm-long plasma with a density of ?2.5x1017 e /cm-3. In recent experiments, energy gains in excess of 10 GeV, by far the largest in any plasma accelerators, have been measured over a plasma length of ?30 cm. Moreover, systematic measurements show the scaling of the energy gain with plasma length and density, and show the reproduceability and the stability of the acceleration process. These are key steps toward the application of beam-driven plasma accelerators or plasma wakefield accelerators (PWFA) to doubling the enregy of a future linear collider without doubling its length. We are preparing for experiments to be performed in February-March 2006 aiming at doubling the energy of the 28.5 GeV beam over a plasma length of less than one meter, a distance two thousand times shorter than the accelerator that created the incoming beam. The latest experimental results will be presented.
*M. J. Hogan et al. Phys. Rev. Lett. 95, 054802, 2005.
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Transparencies
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| WEPLS028 |
Improvement of Electron Generation from a Laser Plasma Cathode through Modified Preplasma Conditions Using an Artificial Prepulse
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2448 |
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- K. Kinoshita, T. Hosokai, K. Kobayashi, A. Maekawa, T. Ohkubo, T. Tsujii, M. Uesaka
UTNL, Ibaraki
- A. Yamazaki
KURRI, Osaka
- A.G. Zhidkov
NIRS, Chiba-shi
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We have been studying the effects of laser prepulses, plasma cavity formation, wave breaking processes in the laser plasma acceleration. It is important to control the preplasma conditions, so as to stabilize the laser plasma acceleration. The modification of the conditions of the laser plasma interaction through an artificial prepulse, magnetic fields, and/or gas density modulation will affect on the characteristics of accelerated electron beams. As the first step, we carry out experiments with an artificial prepulse. If a shockwave driven by the artificial prepulse matches the main pulse foccal position, localized wave breaking may occur effectively, and consequent electron generation will be enhanced. We use a pulse with 10% energy of the main pulse and 300 ps duration to be focused on the interaction point of the gas jet, to change the plasma distribution there. Using the single-shot diagnosis, we investigate the mechanism and technique to improve the properties of electron beams. We observed a strong correlation between the generation of monoenergetic electrons and optical guiding of the main pulse, during the interaction of 11 TW 37 fs laser pulse and He gas jet.
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| WEPLS029 |
Monoenergetic 200fs (FWHM) Electron Bunch Measurement from the Laser Plasma Cathode
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2451 |
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- A. Maekawa, T. Hosokai, K. Kinoshita, K. Kobayashi, T. Ohkubo, T. Tsujii, M. Uesaka
UTNL, Ibaraki
- Y. Kondo, Y. Shibata
Tohoku University, Sendai
- T. Takahashi, A. Yamazaki
KURRI, Osaka
- A.G. Zhidkov
NIRS, Chiba-shi
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A laser plasma accelerator is the most promising approach to compact accelerators that can generate femtosecond electron bunches. It is expected that the electron bunch duration less than 100fs can be achieved owing to the high frequency of plasma waves. Since the time-resolution of the fastest streak camera is only 200fs, we have to use the coherent transition radiation (CTR) measurement or E/O (electro-optical) method. We plan to perform a single-shot measurement by getting the whole CTR spectrum by a IR polychromator in near future. As the first step forward it, we used a IR bolometer with different filters and obtained the average spectrum. We can generate monoenergetic electron bunches in the condition of laser intensity 3x1019W/cm2 and electron density 6x1019cm-3. The charge is estimated to be about 10pC using ICT (Integrated Current Transformer). The electron bunch accelerated by plasma waves penetrates 300um Ti-foil, and transition radiation is emitted. We measure CTR spectrum using a bolometer. Spectrum distribution of CTR depends on the electron bunch distribution, therefore we can evaluate the bunch duration from it. In the experiment, bunch duration can be estimated.
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| WEPLS032 |
Spin Tracking at the ILC
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2454 |
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- G.A. Moortgat-Pick, I.R. Bailey, D.P. Barber, J.A. Clarke, J.B. Dainton, O.B. Malyshev, G.A. Moortgat-Pick, D.J. Scott
Cockcroft Institute, Warrington, Cheshire
- E. Baynham, T.W. Bradshaw, A.J. Brummitt, F.S. Carr, Y. Ivanyushenkov, J. Rochford
CCLRC/RAL, Chilton, Didcot, Oxon
- P. Cooke, L.I. Malysheva
Liverpool University, Science Faculty, Liverpool
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Polarized beams will play a key role in the physics programme at the International Linear Collider (ILC). It is expected that the electron and positron sources will be able to produce beams with polarizations of about 90% and 60% respectively. However, to obtain accurate measurements it is essential to have precise knowledge and control of the polarization at the interaction point itself. It follows that the theoretical calculations used for spin tracking must be guaranteed to match the anticipated 0.1% relative measurement uncertainty of the polarimeters. To meet this need, the heLiCal collaboration is developing a computer simulation to track the evolution of the polarization of bunches of electrons and positrons from the sources to the interaction point. We have studied the beam spin dynamics throughout the ILC including spin precession and radiative spin-flip processes in the positron source, damping rings, beam delivery system and the interaction region. We present the result of these studies with special emphasis on the impact of new theoretical calculations for the CAIN bunch-bunch simulation including full spin correlations and higher-order contributions.
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| WEPLS033 |
Cold Atom Electron Sources
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- O.J. Luiten, M.P. Reijnders, G. Taban, E.J.D. Vredenbregt, S.B. van der Geer
TUE, Eindhoven
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We are developing a completely new method of producing high-brightness electron bunches, based on extraction of electrons from an ultra-cold plasma, created by photo-ionization of a cloud of laser-cooled atoms*. In this way extremely low thermal emittances (<0.1 micron) can be reached at bunch charges of several pC. In addition, pulsed extraction leads to fs bunch lengths and tens of A peak currents without the use of ultra-fast lasers or magnetic compression. GPT simulations in realistic settings show that orders of magnitude in beam brightness may be gained compared to state-of-the-art rf photoguns. Experiments are underway, whose status will be reported.
*B. J. Claessens et al. Phys. Rev. Lett. 95, 164801 (2005).
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| WEPLS038 |
Design of Diamond-lined Accelerator Structure Test Cavity
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2457 |
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- C. Wang, V.P. Yakovlev
Omega-P, Inc., New Haven, Connecticut
- J.L. Hirshfield, M.A. LaPointe
Yale University, Physics Department, New Haven, CT
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For a high-gradient normal-conducting accelerator structure for a future multi-TeV linear collider, the main limitation to achievement of high acceleration gradient is RF breakdown. In an attempt to increase the gradient beyond limits that are acceptable for metallic structures, a diamond-lined structure is suggested. The published DC breakdown limit for CVD diamond is ~2 GV/m, but the limit has never been determined for RF fields. Here we present a design for a 34-GHz diamond-lined rectangular test cavity, operating in the symmetric LSM-1,1,6 mode with symmetric side input couplers. The goal is to produce as high electric fields as possible (approaching 1 GV/m) at the diamond surfaces with ~10 MW of input power supplied by the Omega-P/Yale 34-GHz magnicon for experiment test of dielectric strength.
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| WEPLS039 |
Developments on a Diamond-based Cylindrical Dielectric Accelerating Structure
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2460 |
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- A. Kanareykin, C.-J. Jing
Euclid TechLabs, LLC, Solon, Ohio
- M.E. Conde, W. Gai, J.G. Power
ANL, Argonne, Illinois
- P. Schoessow
Tech-X, Boulder, Colorado
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Developments on a high gradient diamond-based cylindrical dielectric loaded accelerator (DLA) is presented. A diamond-loaded DLA can potentially sustain accelerating gradients far in excess of the limits experimentally observed for conventional metallic accelerating structures. The electrical and mechanical properties of diamond make it an ideal candidate material for use in dielectric accelerators: high RF breakdown level, extremely low dielectric losses and the highest available thermoconductive coefficient. We used the hot-filament Chemical Vapor Deposition (CVD) process to produce high quality 5-10 cm long cylindrical diamond layers. Our collaboration has also been developing a new method of CVD diamond surface preparation that reduces the secondary electron emission coefficient below unity. Special attention was paid to the numerical optimization of the coupling section, where the surface magnetic and electric fields were minimized relative to the accelerating gradient and within known metal surface breakdown limits.
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| WEPLS040 |
Progress towards an Experimental Test of an Active Microwave Medium Based Accelerator
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2463 |
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- A. Kanareykin
Euclid TechLabs, LLC, Solon, Ohio
- P. Schoessow
Tech-X, Boulder, Colorado
- L. Schächter
Technion, Haifa
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We have been working on an experimental test of the PASER concept, where an active medium is used to provide the energy for accelerating charged particles. Initial theoretical work in this area focused on acceleration at optical frequencies; however we have identified a candidate active material operating in the X-band: a solution of fullerene (C60) in a nematic liquid crystal has been found to exhibit a maser transition* in this frequency range. The ability to employ a microwave frequency material simplifies the construction of test structures and allows beam experiments to be performed with relatively large beam emittances. We will report results on synthesis and testing of the active material using EPR spectroscopy, design and numerical simulations of bench test structures and plans for future beam experiments.
*A. Blank et al. IEEE Trans. Microwave Theory and Techniques 46 (2137) 1998.
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| WEPLS042 |
Design and Experimental Investigation of an X-band Multilayer Dielectric Accelerating Structure
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2466 |
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- A. Kanareykin, C.-J. Jing, P. Schoessow
Euclid TechLabs, LLC, Solon, Ohio
- W. Gai, J.G. Power
ANL, Argonne, Illinois
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A new project to significantly improve the efficiency of high gradient DLA structures is presented. A multilayer DLA where the single dielectric layer is replaced by a multiple coaxial layers of differing permittivity have been developed. The power attenuation in the multilayer structure is reduced by the Bragg Fiber principle where the dielectric layers are used to create multiple reflections in order to confine the accelerating mode fields for the most part in the dielectric, reducing the axial current on the conducting outer boundary. A design for an X-band multilayer structure operating in the TM03 mode using alternating dielectric layers with permittivities of 38 and 9.7 is discussed. In order to transfer the RF from the rectangular waveguide to the cylindrical one at TM03 mode, a special coupling and mode conversion scheme was developed. A prototype structure has been constructed and bench test results of the multilayer 11.424 GHz accelerator is presented.
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| WEPLS063 |
Laser Driven Linear Collider
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- A.A. Mikhailichenko
Cornell University, Department of Physics, Ithaca, New York
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We represent the details of scheme allowing long term acceleration with >10GeV/m. The basis of the scheme is a fast sweeping device for laser bunch. After sweeping the laser bunch has a slope with respect to the direction of propagation. So the every cell of accelerating structure becomes illuminated locally only for the moment, when the particle is there. Self consistent parameters allow considering this type of collider as a candidate for post-ILC era.
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