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| TUOBG01 |
Observations of Beam-beam Tune Spectrum and Measurement of Coherent Tune Shift at KEKB
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962 |
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- T. Ieiri, Y. Ohnishi, M. Tobiyama, S. Uehara
KEK, Ibaraki
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KEKB is a double-ring electron/positron collider with a horizontal crossing angle. The crab cavities installed in 2007 achieved an effective head-on collision and gained a higher specific luminosity. Under the new crabbing collision as well as the horizontal crossing collision, tune spectra of a colliding bunch were observed on a spectrum analyzer to study beam-beam effects. The beam-beam spectrum showed strong nonlinear resonant phenomena. Considering the nonlinearity, the coherent beam-beam tune shift was measured as a function of the bunch current. It was confirmed that the vertical beam-beam parameter estimated from the coherent beam-beam tune shift agreed with a value obtained from a bunch-by-bunch luminosity monitor. The estimated vertical beam-beam parameter was saturated on a level of about 0.04, which is called a beam-beam limit. We found that the bunch current corresponding to the beam-beam limit was far below the bunch current used in the usual operation.
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| TUOBG02 |
Study of Beam Dynamics During the Crossing of Resonances in the VEPP-4M Storage Ring
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965 |
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- P. A. Piminov, V. A. Kiselev, E. B. Levichev, O. I. Meshkov, S. A. Nikitin
BINP SB RAS, Novosibirsk
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The influence of resonances on the beam dynamics in the storage rings is of a substantial interest for the accelerator physics. For example, a fast crossing of resonances occurs in the damping rings of future linear colliders during the beam damping due to the coherent shift that can result in a loss of particles. We have studied experimentally the crossing of resonances of different power nearby the working point of the VEPP-4M storage ring. The observation of the beam sizes and particle losses has been done with a single-turn time resolution. The comparison with the numerical simulation has been made.
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| TUOBG03 |
Electron Beam Dynamics in the Long-pulse, High-current DARHT-II Linear Induction Accelerator
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968 |
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- C. Ekdahl, E. O. Abeyta, P. Aragon, R. D. Archuleta, G. V. Cook, D. Dalmas, K. Esquibel, R. J. Gallegos, R. W. Garnett, J. F. Harrison, E. B. Jacquez, J. Johnson, B. T. McCuistian, N. Montoya, S. Nath, K. Nielsen, D. Oro, L. J. Rowton, M. Sanchez, R. D. Scarpetti, M. Schauer, G. J. Seitz, H. V. Smith, R. Temple
LANL, Los Alamos, New Mexico
- H. Bender, W. Broste, C. Carlson, D. Frayer, D. Johnson, C.-Y. Tom, C. P. Trainham, J. T. Williams
NSTec, Los Alamos, New Mexico
- T. C. Genoni, T. P. Hughes, C. H. Thoma
Voss Scientific, Albuquerque, New Mexico
- B. A. Prichard, M. E. Schulze
SAIC, Los Alamos, New Mexico
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We are now operating the full-scale DARHT-II linear induction accelerator (LIA) at its rated energy, accelerating 2-kA electron beams to more than 17 MeV. The injector produces a beam pulse with a full-width at half maximum (FWHM) greater than 2.5 microseconds, and a ~0.5 microsecond rise time. This long risetime is deliberately scraped off in a special beam-head cleanup zone (BCUZ) before entering the 68-cell main accelerator. The accelerated electron beam pulse has a flat-top region where the final electron kinetic energy varies by less than 1% for more than 1.5 microseconds. We will discuss the tuning of the injector, BCUZ, and accelerator; and we will present data for the resulting beam transport and dynamics. We will also present beam stability data, which we will relate to previous stability experiments at lower current and energy*.
*Carl Ekdahl et al. "Long-pulse beam stability experiments on the DARHT-II linear induction accelerator," IEEE Trans. Plasma. Sci. Vol. 34, 2006, pp. 460-466.
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| TUOBG04 |
A Vlasov-Maxwell Solver to Study Microbunching Instability in the FERMI@ELETTRA First Bunch Compressor System
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971 |
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- G. Bassi
Liverpool University, Science Faculty, Liverpool
- G. Bassi
Cockcroft Institute, Warrington, Cheshire
- J. A. Ellison, K. A. Heinemann
UNM, Albuquerque, New Mexico
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Microbunching can cause an instability which degrades beam quality. This is a major concern for free electron lasers where very bright electron beams are required. A basic theoretical framework for understanding this instability is the 3D Vlasov-Maxwell system. However, the numerical integration of this system is computationally too intensive at the moment. As a result, investigations to date have been done using very simplified analytical models or numerical solvers based on simple 1D models. We have developed an accurate and reliable 2D Vlasov-Maxwell solver which we believe improves existing codes. Our solver has been successfully tested against the Zeuthen benchmark bunch compressors*. In the present contribution we apply our self-consistent, parallel solver to study the microbunching instability in the first bunch compressor system of FERMI@ELETTRA. This system was proposed as a benchmark for testing codes at the September'07 workshop on microbunching instability in Trieste**.
*PAC2007, papers TUZBC03 and THPAN084.
**https://www.elettra.trieste.it/FERMI/index.php?n=Main. MicrobProgram
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