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| MOP62 |
Energy Spread in BTW Accelerating Structures at ELETTRA
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159 |
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- P. Craievich, R.J. Bakker, G. D'Auria, S.D. Di Mitri
Sincrotrone Trieste S.C.p.A., Basovizza, Trieste
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The FEL project FERMI@ELETTRA will use the existing 1.0 GeV Linac, based on Backward Travelling Wave (BTW) structures, to produce VUV radiation between 100–10 nm. The project will be articulated in two different phases (100–40 nm/40–10 nm) and will require high quality beam with short bunches (500/160 fsec). Hence, wakefield effects have to be considered with respect to the electron beam quality. The single bunch energy spread induced by the short-range longitudinal wakefield is analyzed and results of start-to-end simulations are reported.
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| MOP63 |
Numerical Calculation of Coupling Impedances in Kicker Modules for Non-Relativistic Particle Beams
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162 |
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- B. Doliwa, T. Weiland
TU Darmstadt, Darmstadt
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In the context of heavy-ion synchrotrons, coupling impedances in ferrite-loaded structures (e.g. fast kicker modules) are known to have a significant influence on beam stability. While bench measurements are feasible today, it is desirable to have the coupling impedances in hands already during the design process of the respective components. To achieve this goal, as a first step, we have carried out numerical analyses of simple ferrite-containing test systems within the framework of the Finite Integration Technique[1]. This amounts to solving the full set of Maxwell's equations in frequency domain, the particle beam being represented by an appropriate excitation current. With the resulting electromagnetic fields, one may then readily compute the corresponding coupling impedances. Despite the complicated material properties of ferrites, our results show that their numerical treatment is possible, thus opening up a way to determine a crucial parameter of kicker devices before construction.
[1] Weiland, T., Electronics and Communication (AEÜ), Vol. 31 (1977), p. 116.
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| MOP64 |
Wire Measurement of Impedance of an X-Band Accelerating Structure
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165 |
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- N. Baboi
DESY, Hamburg
- G. Bowden, V.A. Dolgashev, R.M. Jones, J. Lewandowski, S.G. Tantawi, J. Wang
SLAC/ARDA, Menlo Park, California
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Several tens of thousands of accelerator structures will be needed for the next generation of linear collders known as the GLC/NLC (Global Linear Collider/Next Linear Collider). To prevent the beam being driven into a disruptive BBU (Beam Break Up) mode or at the very least, the emittance being signifcantly diluted, it is important to damp down the wakefield left by driving bunches to a manageable level. Manufacturing errors and errors in design need to be measurable and compared with predictions. We develop a circuit model of wire-loaded X-band accelerator structures. This enables the wakefield (the inverse transform of the beam impedance) to be readily computed and compared with the wire measurement. We apply this circuit model to the latest series of accelerating for the GLC/NLC. This circuit model is based upon the single-cell model developed in [1] extended here to complete, multi-cell structures.
[1] R.M. Jones et al, 2003, Proc. PAC2003 (also SLAC-PUB 9871)
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| MOP65 |
Simple Theory of Thermal Fatigue Caused by RF Pulse Heating
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168 |
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- S. Kuzikov
IAP, Nizhniy Novgorod
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The projects of electron-positron linear colliders imply that accelerating structures and other RF components will undergo action of extremely high RF fields. Except for breakdown threat there is an effect of the damage due to multi-pulse mechanical stress caused by Ohmic heating of the skin layer. A new theory of the thermal fatigue is considered. The theory is based on consideration of the quasi-elastic interaction between neighbor grains of metal due to the expansion of the thermal skin-layer. The developed theory predicts a total number of the RF pulses needed for surface degradation in dependence on temperature rise, pulse duration, and average temperature. The unknown coefficients in the final formula were found, using experimental data obtained at 11.4 GHz for the copper. In order to study the thermal fatigue at higher frequencies and to compare experimental and theoretical results, the experimental investigation of degradation of the copper cavity exposed to 30 GHz radiation is carried out now, basing on a 30 GHz free electron maser.
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| MOP66 |
Calculation of RF Properties of the Third Harmonic Cavity
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171 |
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- K. Rothemund, D. Hecht, U. van Rienen
Rostock University, Faculty of Engineering, Rostock
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Recently a third harmonic structure has been proposed for the injector of the TTF-FEL to avoid nonlinear distortions in the longitudinal phase space. This structure, consists of four nine cell TESLA-like cavities. For the use of this structure in combination with the TTF-FEL it might be interesting to investigate higher order modes (HOM) in the structure and their effect on the beam dynamics. The complexity of the structure, four nine cell cavities assembled with four input couplers and eight HOM-couplers, results in an extremely high numerical effort for full 3D modelling. Therefor Coupled S-Parameter Calculation (CSC) [1] has been applied. This method is based on the scattering parameter description of the rf components found with field solving codes or analytically for components of special symmetry. This paper presents the results of the calculation of rf properties (e.g. scattering parameters, Q-values) of the complete four times nine cell structure equipped with all input- and HOM-couplers.
[1] H.-W. Glock, K. Rothemund, U. van Rienen, CSC - A Procedure for Coupled S-Parameter Calculations, IEEE Trans. Magnetics, vol. 38, pp. 1173 - 1176, March 2002
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| MOP67 |
TESLA RF Power Coupler Thermal Calculations
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174 |
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- D. Kostin, M. Dohlus, W.-D. Möller
DESY, Hamburg
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The main RF power coupler is one of the key elements of the accelerating module for the superconducting linac. It provides RF power to the cavity and interconnect different temperature layers in the module. Therefore statistical and dynamical thermal losses have to be optimized. Different operating modes as well as geometries were investigated. Coupler design optimization studies are carried out for TESLA and for the XFEL case. Especially long pulse operation for the X-FEL is being investigated.
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| MOP68 |
Ribbon Ion Beam Dynamics in Undulator Linear Accelerator
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177 |
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- E.S. Masunov, S.M. Polozov
MEPhI, Moscow
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The possibility to use radio frequency undulator fields for ion beam focusing and acceleration in linac (UNDULAC-RF) is discussed. In periodical resonator structure the accelerating force is produced by the combination of two or more space harmonics of a longitudinal or a transverse undulator field*. The particle motion equations in Hamilton form are carried out by means of smooth approximation. The analysis of 3D effective potential permits to find the conditions under which focusing and acceleration of the particles occur simultaneously. The analytical results are verified with a numerical simulation. Examples illustrating the efficiency of the proposed method of acceleration are given for longitudinal and transverse undulators. The results are compared with a conventional linac and the other possibility of ion beam acceleration in UNDULAC-E(M) where electrostatic and magnetic fields are used.
*E.S. Masunov, Technical Physics, Vol. 46, No.11, 2001, pp. 1433-1436.
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| MOP69 |
RF Control Modelling Issues for Future Superconducting Accelerators
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180 |
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- A. Hofler, J. R. Delayen
TJNAF, Newport News, Virginia
- V. Ayvazyan, A. Brandt, S. Simrock
DESY, Hamburg
- T. Czarski
WUT, Warsaw
- T. Matsumoto
KEK, Ibaraki
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The development of superconducting accelerators has reached a high level of maturity following the successes of ATLAS at Argonne, CEBAF at Jefferson Lab, the TESLA Test Facility at DESY and many other operational accelerators. As a result many new accelerators under development (e.g. SNS) or proposed (e.g. RIA) will utilize this technology. Covering all aspects from cw to pulsed rf and/or beam, non-relativistic to relativistic particles, medium and high gradients, light to heavy beam loading, linacs, rings, and ERLs, the demands on the rf control system can be quite different for the various accelerators. For the rf control designer it is therefore essential to understand these issues and be able to predict rf system performance based on realistic rf control models. This paper will describe the features that should be included in such models and present an approach which will drive the development of a generic rf system model.
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| MOP70 |
A Pass Band Performance Simulation Code of Coupled Cavities
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183 |
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- X. Tao, D. Tong
TSINGHUA, Beijing
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A simulation code of accelerating cavities named PPSC is developed by the solutions of the microwave equivalent circuit equations. PPSC can give the pass band performance of periodic or non-periodic accelerating structures, such as the dispersion frequency and the reflection factor of the cavity, the field distribution of each mode and so on. The natural parameters of the structure, such as the number of the cavities, the resonant frequencies and Q-factors of each cavity, the coupling factor between two cavities, and the locations of the couplers, can be changed easily to see the different results of the simulation. The code is written based on MS Visual Basic under MS windows. With these, a user-friendly interface is made. Some simple examples was simulated and gave reliable results.
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| MOP71 |
Advanced Beam-Dynamics Simulation Tools for RIA
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186 |
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- T.P. Wangler, R. Garnett
LANL, Los Alamos, New Mexico
- N. Aseev, P.N. Ostroumov
ANL/Phys, Argonne, Illinois
- R. Crandall
TechSource, Santa Fe, NM
- D. Gorelov, R.C. York
NSCL, East Lansing, Michigan
- J. Qiang, R. Ryne
LBNL, Berkeley, California
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Understanding beam losses is important for the high-intensity RIA driver linac. Small fractional beam losses can produce radioactivation of the beamline components that can prevent or hinder hands-on maintenance, reducing facility availability. Operational and alignment errors in the RIA driver linac can lead to beam losses caused by irreversible beam-emittance growth and halo formation. We are developing multiparticle beam-dynamics simulation codes for RIA driver-linac simulations extending from the low-energy beam transport (LEBT) line to the end of the linac. These codes run on the NERSC parallel supercomputing platforms at LBNL, which allow us to run simulations with large numbers of macroparticles for the beam-loss calculations. The codes have the physics capabilities needed for RIA, including transport and acceleration of multiple-charge-state beams, and beam-line elements such as high-voltage platforms within the linac, interdigital accelerating structures, charge-stripper foils, and capabilities for handling the effects of machine errors and other off-normal conditions. We will present the status of the work, including examples showing some initial beam-dynamics simulations.
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| MOP72 |
RF Breakdown in Accelerator Structures: From Plasma Spots to Surface Melting
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189 |
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- P.B. Wilson
SLAC, Menlo Park, California
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Plasma spots are known to form at field emission sites in regions of high dc or rf electric field. Several mechanisms for the formation of plasma spots in an rf field have been proposed, and one such mechanism which fits experimental data is presented in this paper. However, a plasma spot by itself does not produce breakdown. A single plasma spot, with a lifetime on the order of 30 ns, extracts only a negligible amount of energy from the rf field. The evidence for its existence is a small crater, on the order of 10 microns in diameter, left behind on the surface. In this paper we present a model in which plasma spots act as a trigger to produce surface melting on a macroscopic scale (~0.1 mm2). Once surface melting occurs, a plasma that is capable of emitting several kiloamperes of electrons can form over the molten region. A key observation that must be explained by any theory of breakdown is that the probability of breakdown is independent of time within the rf pulse–breakdown is just as likely to occur at the beginning of the pulse as toward the end. In the model presented here, the conditions for breakdown develop over many pulses until a critical threshold for breakdown is reached.
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Transparencies
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| THP21 |
Calculation of Electron Beam Dynamics of the LUE-200 Accelerator
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639 |
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- A.P. Sumbaev, V. Alexandrov, N.Y. Kazarinov, V.F. Shevtsov
JINR, Dubna, Moscow Region
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The results of calculations of the focusing and transportation systems of the electron beam of LUE-200 accelerator – the driver of a pulse source of resonant neutrons IREN, JINR (Dubna), are presented. Simulations of the beam dynamics in the traveling wave accelerator were carried out by means of PARMELA code. The calculations have been fulfilled for various parameters of the focusing magnetic fields in the accelerator and the channel, various currents of the beam and various initial distributions of electrons.
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| THP22 |
3D Beam Dynamics Simulation in Undulator Linac
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642 |
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- E.S. Masunov, S.M. Polozov
MEPhI, Moscow
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The ion beam can be bunched and accelerated in linear accelerator with RF undulator (UNDULAC-RF). The acceleration and focusing of beam can be realized without using a synchronous wave*. In this paper the computer simulation of high intensity ion beam dynamics in UNDULAC-RF was carried out by means of the "superparticles" method. The computer simulation and optimization of ion dynamics consist of two steps. At the first, the equations of particles motion in polyharmonic fields are devised by means of smooth approximation. Hamiltonian analysis of these equations allows to find a velocity of reference particle in polyharmonic field and to formulate the conditions of good longitudinal bunching and transverse focusing beam. At the second, the 3D ion beam dynamics simulation in an UNDULAC is governed by founded functions of reference particle velocity and a ratio of amplitude harmonics. The influence of the space charge on RF focusing conditions, transmission coefficient, longitudinal and transverse emittances, and other acceleration system characteristics are investigated by computer simulation.
*Masunov E.S., Sov. Phys.-Tech. Phys., vol. 35, No. 8, p. 962, 1990.
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| THP93 |
A 3D Self-Consistent, Analytical Model for Longitudinal Plasma Oscillation in a Relativistic Electron Beam
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818 |
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- G. Geloni, E. Saldin, E. Schneidmiller, M.V. Yurkov
DESY, Hamburg
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Longitudinal plasma oscillations are becoming a subject of great interest for XFEL physics in connection with LSC microbunching instability[1] and certain pump-probe synchronization schemes[2]. In the present paper we developed the first exact analytical treatment for longitudinal oscillations within an axis-symmetric, (relativistic) electron beam, which can be used as a primary standard for benchmarking space-charge simulation codes. Also, this result is per se of obvious theoretical relevance as it constitutes one of the few exact solutions for the evolution of charged particles under the action of self-interactions.
[1] E. Saldin et al., "Longitudinal Space Charge Driven Microbunching instability in TTF linac", TESLA-FEL-2003-02, May 2003, [2] J. Feldhaus et al., "Two-color FEL amplifier for femtosecond-resolution pump-probe experiments with GW-scale X-ray and optical pulses",DESY 03-091, July 2003
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| FR203 |
The Science of Radioactive Ion Beams
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857 |
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- B. Sherrill
NSCL, East Lansing, Michigan
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The primary intellectual challenge of nuclear physics is to understand the nature of strongly interacting matter and how the features of nuclear many-body systems derive from the fundamental forces and properties of their constituent parts. In nuclear science, interestingly, atomic nuclei present one of the most difficult problems to address. However, a comprehensive understanding of nuclear properties is essential to our ability to model the chemical evolution of the Universe, use nuclei for tests of the fundamental symmetries of nature and assess any number of nuclear technologies. Until recently, the fact that experiments had to be carried out with the limited range of stable isotopes found in nature has severely constrained our understanding. However, the current and next generation of radioactive ion beam facilities will remove this constraint. This talk will endeavor to summarize the most important opportunities made available with the next generation of radioactive ion beam facilities.
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Transparencies
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