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| MOPLT135 |
Damping the High Order Modes in the Pumping Chamber of the PEP-II Low Energy Ring
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positron, vacuum, damping, impedance |
854 |
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- A. Novokhatski, S. Debarger, F.-J. Decker, A. Kulikov, J. Langton, M. Petree, J. Seeman, M.K. Sullivan
SLAC, Menlo Park, California
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The Low Energy Ring of the PEP-II B-factory operates with extremely high currents and short positron bunches. Any discontinuity in the vacuum chamber can excite a broad-band spectrum of the High Order Modes. A temperature rise has been found in the vacuum chamber elements in one transition from straight section to arc. The power in the wake fields was high enough to char beyond use the feed-through for the Titanium Sublimation Pump. This pumping section consists of the beam chamber and an ante-chamber. Fields, excited in the beam chamber penetrate to the ante-chamber and then through the heater wires of the TSP come out. A small ceramic tile was placed near the TSP feed-through to absorb these fields. A short wire antenna was also placed there. HOM measurements show a wide spectrum with a maximum in the 2-3 GHz region. A special water cooled HOM absorber was designed and put inside the ante-chamber part of the section. As a result, the HOM power in the section decreased and the temperature rise went down. The power loss is 750 W for a beam current of 2 A. Measurements of the HOM impedance for different bunch patterns, bunch length and transverse beam position will be presented.
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| TUPKF014 |
Electromagnetic Design of New RF Power Couplers for the S-DALINAC
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electron, emittance, linac, coupling |
988 |
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- M. Kunze, W.F.O. Müller, T. Weiland
TEMF, Darmstadt
- M.B. Brunken, H.-D. Gräf, A. Richter
TU Darmstadt, Darmstadt
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New rf power couplers for the Superconducting Darmstadt Linear Accelerator (S-DALINAC) injector have to be designed to transfer rf power up to 2 kW to the electron beam. This allows injector operation at beam currents from 0.15 mA to 0.2 mA and electron energies up to 14 MeV. The new couplers should possibly provide a variable external Q in the range from 5·106 to 3·109 and a small transverse kick. A variable coupling is needed to allow for perfect matching in the case of beam loading and when no beam is present, respectively. The second operation stage is used for cavity diagnostics. The asymmetric field distribution of the couplers generates emittance growth of the electron beam and therefore the transverse kick has to be minimized. Electromagnetic simulations are applied to investigate different coupler designs and to localize possible problems at an early stage. Cavity external Q and transverse kick can be calculated from 3D electromagnetic eigenmode solutions. The present coaxial-coaxial input couplers at the S-DALINAC are limited to power operation below 500 W under full reflection. Therefore, to reach power operation up to 2 kW two possible new realizations of low-kick waveguide couplers for the S-DALINAC injector are presented, namely a single-waveguide and a twin-waveguide coupler.
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| WEOALH01 |
Particle-in-cell Beam Dynamics Simulations
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simulation, damping, cathode, space-charge |
170 |
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- T. Lau, E. Gjonaj, T. Weiland
TEMF, Darmstadt
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We describe the application of the Conformal Finite Integration Technique (CFIT) in the time-domain to beam dynamics simulations with the Particle-In-Cell (PIC) method. The conformal method results in a more accurate field solution for complicated geometries than the traditional FIT approach. For long-time simulations we investigate several methods for the suppression of the spurious noise, typically emerging in PIC simulations. The results are compared with the analytical solution for a bunch in a semi-infinite waveguide for each of the presented methods. As a realistic example simulations for the RF-Gun installed at Photo Injector Test Facility in DESY Zeuthen (PITZ) will be presented.
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Video of talk
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Transparencies
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| WEPLT062 |
Wakefield Calculations for TTF-II
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impedance, linac, diagnostics, dipole |
1987 |
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- I. Zagorodnov, T. Weiland
TEMF, Darmstadt
- M. Dohlus
DESY, Hamburg
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In this paper we estimate long- and short-range wake functions for new elements to be used in TESLA Test Facility (TTF) - II. The wake potentials of the LOLA-IV structure and the 3rd harmonic section are calculated numerically for very short bunches and analytical approximations for wake functions in short and long ranges are obtained by fitting procedures based on analytical estimations. The numerical results are obtained with code ECHO for high relativistic Gaussian bunches with RMS deviation up to 0.015 mm. The calculations are carried out for the complete structures (including bellows, rounding of the irises and the different end cell geometries) supplied with ingoing and outgoing pipes. The low frequency spectra of the wake potentials is calculated using the Prony-Pisarenko method.
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| WEPLT093 |
Electromagnetic Fields of an Off-axis Bunch in a Circular Pipe with Finite Conductivity and Thickness - I
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multipole, vacuum, injection, single-bunch |
2068 |
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- S. Petracca, L. Cappetta, T. Demma
U. Sannio, Benevento
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The electromagnetic field produced by a bunched beam in a circular pipe is usually computed under the assumption that the field penetration(skin depth) is far less than the wall thickness. Chao [*] gave a formula which exploits the wall thickness, but his result is restricted to the monopole term. Piwinski [**] treated the case of a metal coated ceramic wall, when the coating thickness is much smaller than the skin-depth, but his analysis is also limited to the monopole term.In this paper we solve the problem in full generality, by providing an exact (Green's functions) solution for the field of an off-axis point particle running at constant velocity in a circular pipe with finite wall conductivity and thickness.
* A.W. Chao, Phys. of Collective Beam Instab. in High En. Accel., Wiley,1993** S. Piwinski, DESY 1972/72
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| WEPLT094 |
Electromagnetic Fields of an Off-axis Bunched Beam in a Circular Pipe with Finite Conductivity and Thickness - II
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multipole, quadrupole, collider, hadron |
2071 |
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- S. Petracca, L. Cappetta, T. Demma
U. Sannio, Benevento
- R.P. Croce
Universita' degli Studi di Salerno, Dipartimento di Fisica E.R. Caianiello, Baronissi
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The general exact solution exploited [*] is applied, introducing suitable dimensionless parameters, and using appropriate asymptotic limiting forms, to compute the wake field multipoles for the different paradigm cases of LHC and DAPHNE.
* R. P. Croce, Th. Demma, S. Petracca "Electromagnetic Fields of an Off-axis Bunch in a Circular Pipe with Finite Conductivity and Thickness", these proceedings
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| WEPLT171 |
Rotating Electromagnetic Field Trap for High Temperature Plasma and Charge Confinement
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electron, laser, quadrupole, plasma |
2230 |
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- V.V. Danilov
ORNL/SNS, Oak Ridge, Tennessee
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This paper demonstrates that there exists a special combination of oscillating electromagnetic fields capable of trapping ultra high charge densities. Trapped particles undergo stable motion when their frequencies of oscillation are much higher than that of the ocillating field. Contrary to conventional electromagnetic traps, the motion in this dynamic trap is stable for arbitrarily high electromagnetic field amplitudes. This, in turn, leads to the possibility of using enormous electric and magnetic fields from RF or laser sources to confine dense ultrahigh temperature plasmas and particle beams.
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| THPLT004 |
Toroidal Cavity Loaded with an Electron Beam
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radiation, synchrotron, synchrotron-radiation, acceleration |
2463 |
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- E.D. Gazazyan, T. Harutyunyan, D.K. Kalantaryan
YSU, Yerevan
- V. Kocharyan
DESY, Hamburg
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Three problems have been considered in this paper: the development of Maxwell's equations strict solution method to define the electromagnetic own values and own functions of the toroidal cavity; the radiation of the charged bunch rotating along the average radius, and, at last, the consideration of the case of a toroid filled with dielectric medium. The peculiarities of this radiation have been investigated as well. We suppose to consider the case when toroid is filled with plasma like a disperse medium.
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| THPLT029 |
Parallel Particle in Cell Computations with GdfidL
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simulation, vacuum, plasma, acceleration |
2538 |
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- W. Bruns
WBFB, Berlin
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The electromagnetic field solver GdfidL has been extended to compute with free moving charges. For computing in parallel, GdfidL partitions the computational volume in many small subvolumes. Each processor computes the electromagnetic field in its part of the whole volume. In addition to the normal field update equations, the movement of the particles must be computed from the Lorentz-force, and the convection current due to the moving charges must be computed and be used to change the electric field near the particle. For each particle, these computations are performed by the processor which is responsible for the volume where the particle is in. Details of the parallel implementation of the used algorithm, Particle in Cell, are given.
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| THPLT077 |
MPI Parallel Computation of Wake Fields by Using Time Domain Boundary Element Method
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simulation, scattering |
2673 |
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- K. Fujita, H. Kawaguchi
Muroran Institute of Technology, Department of Electrical and Electronic Engineering, Muroran
- T. Weiland, I. Zagorodnov
TEMF, Darmstadt
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This paper presents wake field and wake potential calculation by using the Time Domain Boundary Element Method (TDBEM) on the MPI parallel computation system. The TDBEM is based on the electric field integral equation (EFIE) and the electric field integral equation (MFIE) in time domain. In wake field simulation, an important advantage of these equations is that electromagnetic fields in an accelerator cavity are explicitly expressed as a sum of charged particle self-fields and wake fields in time domain. On the other hand, the TDBEM has serious difficulties in practical numerical simulation, such as numerical instabilities, huge memory requirements, and heavy calculation cost. However, recent remarkable progress of computer performance makes the TDBEM possible to be used in practical simulations. According to these backgrounds, we apply the TDBEM to wake field simulation in the MPI parallel computer system. Simulation results are compared with that of a conventional method, the Finite Integration Techniques (FIT), and good agreements are shown.
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| THPLT085 |
Reengineering and Refactoring Large-scale Scientific Programs with the Unified Process: A Case Study with OSIRIS PIC Program
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diagnostics, simulation, coupling, factory |
2697 |
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- J.B. Kim, I.S. Ko
POSTECH, Pohang, Kyungbuk
- H. Suk
KERI, Changwon
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As science and engineering problems get more complex, programs which help modelling complicated problems larger and more sophisticated. This trend makes us recognize the importance of well-established engineering disciplines not only in designing large-scale scientific programs for special purposes in appropriate development time but also in importing the programs from other research group and refactor it for conveniences and more advanced applications. OSIRIS is a large-scale PIC code which was developed at UCLA for modelling of laser-plasma interactions. OSIRIS was reengineered and documented in UML by our group and ported to Linux cluster machine of 8 nodes. We report our current status of developing the extended version of OSIRIS, which was named as OSIRIS-X, and how a large-scale scientific programs can be enhanced efficiently with the Unified Process. Some guidelines in designing and refactoring large-scale scientific codes are presented and discussed. A common architecture model of numerically intensive programs for large-scale computing is suggested , and it is discussed how we can use it for rapid development and prototyping of scientific programs. We also discuss future challenges and prospects in OSIRIS-X development.
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| THPLT110 |
Modelling of Accelerating Structures with Finite-difference Time-domain Method
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simulation, focusing, acceleration |
2742 |
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| THPLT123 |
Coupling Coefficients in the Inhomogeneous Cavity Chain
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coupling, damping, acceleration |
2759 |
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- K. Kramarenko, M.I. Ayzatskiy
NSC/KIPT, Kharkov
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In this paper a mathematical method on the base of a rigorous electrodynamic approach for description of inhomogeneous chain of cylindrical cavities is presented. The form of the obtained for chosen amplitudes set of equations is similar to the set of equations that describe the simple coupled circuit chain. As the cavity have the infinite number of resonant frequencies, to obtain the coupling coefficients one have to solve additional infinite set of linear equations with coefficients that depend on the frequency. Using the developed method in the case of inhomogeneous cavity chain we calculated the dependence of the coupling coefficients on frequency and geometrical sizes with taking into account the 'long-range' coupling.
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