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| MOM2IS02 |
Large Scale Parallel Wake Field Computations for 3D-Accelerator Structures with the PBCI Code
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simulation, electromagnetic-fields, diagnostics, electron |
29 |
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- E. Gjonaj, X. Dong, R. Hampel, M. Kärkkäinen, T. Lau, W. F.O. Müller, T. Weiland
TEMF, Darmstadt
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Funding: This work was partially funded by EUROTeV (RIDS-011899), EUROFEL (RIDS-011935), DFG (1239/22-3) and DESY Hamburg
The X-FEL project and the ILC require a high quality beam with ultra short electron bunches. In order to predict the beam quality in terms of both, single bunch energy spread and emittance, an accurate estimation of the short range wake fields in the TESLA crymodules, collimators and other geometrically complex accelerator components is necessary. We have presented earlier wake field computations for short bunches in rotationally symmetric components with the code ECHO. Most of the wake field effects in the accelerator, however, are due to geometrical discontinuities appearing in fully three dimensional structures. For the purpose of simulating such structures, we have developed the Parallel Beam Cavity Interaction (PBCI) code. The new code is based on the full field solution of Maxwell equations in the time domain, for ultra-relativistic current sources. Using a specialized directional-splitting technique, PBCI produces particularly accurate results in wake field computations, due to the dispersion free integration of the discrete equations in the direction of bunch motion. One of the major challenges to deal with, when simulating fully three dimensional accelerator components is the huge computational effort needed for resolving both, the geometrical details and the bunch extensions by the computational grid. For this reason, PBCI implements massive parallelization on a distributed memory environment, based on a flexible domain decomposition method. In addition, PBCI uses the moving window technique, which is particularly well suited for wake potential computations in very long structures. As a particular example of such a structure, the simulation results of a complete module of TESLA cavities with eight cells each for a um-bunch will be given.
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| MOM2IS03 |
Low-Dispersion Wake Field Calculation Tools
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simulation, electromagnetic-fields, linac, linear-collider |
35 |
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- M. Kärkkäinen, E. Gjonaj, T. Lau, T. Weiland
TEMF, Darmstadt
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Funding: This work was partially funded by EUROTeV (RIDS-011899), DFG (1239/22-3) and DESY Hamburg.
Extremely short bunches are used in future linear colliders, such as the International Linear Collider (ILC). Accurate and computationally efficient numerical methods are needed to resolve the bunch and to accurately model the geometry. In very long accelerator structures, computational efficiency necessitates the use of a moving window in order to save memory. On the other hand, parallelization is desirable to decrease the simulation times. Explicit schemes are usually more convenient to parallelize than implicit schemes since the implementation of a separate potentially time-consuming linear solver can thus be avoided. Explicit numerical methods without numerical dispersion in the direction of beam propagation are presented for fully 3D wake field simulations and for the special case of axially symmetric structures. The introduced schemes are validated by comparing with analytical results and by providing numerical examples for practical accelerator structures. Conformal techniques to enhance the convergence rate are presented and the advantages of the conformal schemes are verified by numerical examples.
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| MOA1MP03 |
A Framework for Maxwell’s Equations in Non-Inertial Frames Based on Differential Forms
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electromagnetic-fields, acceleration |
47 |
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- S. Kurz
Robert Bosch GmbH, Frankfurt
- B. Flemisch, B. Wohlmuth
IANS, Stuttgart
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In many engineering applications the interaction between the electromagnetic field and moving bodies is of great interest. It is natural to use a Lagrangian description, where the unknowns are defined on a mesh which moves and deforms together with the considered objects. What is the correct form of Maxwell’s equations and the material laws under such circumstances? The aim of the present paper is to tackle this question by using the language of differential forms. We first provide a review of the formulations of electrodynamics in terms of vector fields, as well as differential forms in the (1+3)- and four-dimensional setting. In order to keep both Maxwell’s and the constitutive equations as simple as possible, we set up two reference frames. In the natural material frame, the (1+3)-Maxwell’s equations have their simple form, whereas in the co-moving inertial frame, the material laws are canonical. In contrast to existing literature these frames are both retained to benefit from their individual advantages. It remains to construct transformation laws connecting the considered frames. To achieve this, we use a (1+3)-decomposition in terms of general projection operators which do primarily not depend on an underlying metric or on the choice of a spatial coordinate system [1]. The desired transformation laws are established by comparing the different decompositions of an arbitrary p-form with respect to the considered frames. We provide an interpretation in terms of vector fields, and consider the low frequency limit, which is the most relevant case for an implementation into numerical codes. For the description of low frequency electromagnetism, all rigid frames are equivalent. This goes beyond the standard principle of Galilean relativity, where only inertial frames are regarded as equivalent. The proper treatment in the general case is demonstrated by means of an example in rotating coordinates, where the classical paradox by Schiff [2] is resolved.
[1] F. Hehl and Y. Obukhov, Foundations of Classical Electrodynamics. Boston: Birkhäuser, 2003.
[2] L. Schiff, "A question in general relativity," Proc. Nat. Acad. Sci. USA, vol. 25, 1939.
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| TUMPMP01 |
Simple Maps in Accelerator Simulations
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electron, ion, proton, simulation |
81 |
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- S. Peggs, U. Iriso
BNL, Upton, Long Island, New York
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Difference systems (described by maps) exhibit much richer dynamical behavior than differential systems, because of the emphasis they place on occasional "high-frequency" transient kicks. Thus, the standard map (with pulsed gravity) displays chaos, while the gravity pendulum does not. Maps also speed up simulations enormously, by summarizing complex dynamics in short form. A new example of richer bahavior, and of dramatic speed up, comes from the representation of interacting electron clouds and ion clouds. Coupled maps are capable of demonstrating the first order phase transitions (from cloud "off" to "on") that are sometimes observed in practice, and enable the extension of electron cloud simulation to include much slower evolving ion clouds.
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| TUPPP01 |
DEE Voltage Calibration for the ACCEL Proton Therapy Cyclotron
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cyclotron, electron, proton, extraction |
102 |
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- J. H. Timmer, P. A. Komorowski, H. Röcken
ACCEL, Bergisch Gladbach
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ACCEL Instruments GmbH has developed a superconducting cyclotron for the use in proton therapy systems. An essential step during the commissioning of the medical cyclotron is the calibration and balancing of the DEE voltages. Using a very compact and low cost X-ray detector the bremsstrahlung spectrum of stray electrons accelerated by the four RF cavities has been measured. To determine the peak voltage a regression analysis of the measured spectrum has been carried out using a non-linear multiple convolution model taking into account the energy gain of the stray electrons between the liner and the DEE, the bremsstrahlung spectrum integrated over angle as well as the attenuation effects caused by the liner and the limited detector resolution. The correlation between the model and the measurement was very good. A software tool enabling automatic spectrum acquisition and analysis capable of online determination of the DEE voltages has been developed in LabVIEW graphical programming environment. Careful balancing of the DEE voltages resulted in better beam focusing and a cyclotron extraction efficiency larger than 80%. The absolute acceleration voltage has been confirmed by turn-separation measurements.
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| TUPPP26 |
A Time-Adaptive Mesh Approach for the Self-Consistent Simulation of Particle Beams
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simulation, gun, cathode, emittance |
132 |
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- S. Schnepp, E. Gjonaj, T. Weiland
TEMF, Darmstadt
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Funding: This work was partially funded by HGF (VH-FZ-005) and DESY Hamburg.
In many applications the self-consistent simulation of charged particle beams is necessary. Especially, in low-energetic sections such as injectors the interaction between particles and fields considering all effects has to be taken into account. Well-known programs like the MAFIA TS modules typically use the Particle-In-Cell (PIC) method for beam dynamics simulations. Since they use a fixed computational grid which has to resolve the bunch adequately, they suffer from enormous memory consumption. Therefore and especially in the 3D case, only rather short sections can be simulated. This may be avoided using adaptive mesh refinement techniques (AMR). Since their application in Finite-Difference methods in time-domain is critical concerning instabilities, usually problem-matched but static meshes are used. In this paper a code working on the basis of a fully dynamic Cartesian grid is presented allowing for simulations capturing both, a high spatial resolution in the vicinity of the bunch and the possibility of simulating structures up to a length of several meters. The code is tested and validated using the RF electron gun of the Photoinjector Test Facility at DESY Zeuthen (PITZ) as an example. The evolution of various beam parameters along the gun is compared with the results obtained by different beam dynamics programs.
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| TUAPMP04 |
Simulation of Secondary Electron Emission with CST Particle Studio(TM)
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electron, simulation, electromagnetic-fields, scattering |
160 |
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- F. Hamme, U. Becker, P. Hammes
CST, Darmstadt
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In accelerator physics and high power vacuum electronics the secondary electron emission (SEE) has in many cases an important influence on the physical behavior of the device. Since its analytical prediction even for simple geometries is extremely cumbersome, numerical simulation is essential to get a better understanding of the possible effects and ideas to change the design. The current paper introduces the implementation of SEE within the code CST Particle Studio (TM), which is an easy to use three dimensional tool for the simulation of electromagnetic fields and charged particles. There are three basic types of secondary electrons, the elastic reflected, the rediffused and the true secondary ones. The implemented SEE model is based on a probabilistic, mathematically self-consistent model developed by Furman and includes the three kinds of secondary electrons mentioned above. The paper presents simulation results with focus to the SEE for the absorbed power within an electron collector of a high power tube. As second example the secondary emission process is studied within the superconducting TESLA cavity, which gives some hints for the understanding of multipactor effects in those cavity and filter structures.
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