Publications (11)1.39 Total impact

Chapter: Coupled Calculation of Eigenmodes
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ABSTRACT: In many technical applications the electromagnetic eigenmodes — frequency spectrum and field distributions  of rfcomponents are to be determined during the design process. There are numerous cases where the studied component is too complex to allow for a detailed enough simulation on usual servers. One way out of this situation is domain decomposition and parallelization of the field simulation. Yet, this demands for a parallelized solver. In our approach, we combine the use of commercial single processorbased software for the field simulation with a tool based on scattering parameter description. The studied component is decomposed in several sections. The scattering matrices of these sections are computed in time domain for instance with a FDTD field solver. A linear system is set up to compute the eigenfrequencies of the complete system and the field amplitudes at the internal ports common to a pair of sections. With the knowledge of these amplitudes the fields of the eigenmodes can be computed with help of a frequency domain field solver. This approach is denoted as Coupled SParameter Calculation (CSC). Some advantages of this procedure are the possibility of easy exploitation of symmetries in the studied components and the use of very different granularities in discretization of the single sections. This paper presents the method, its validation using a standard eigenmode solver and applications in the field of accelerator physics. Special attention is given to the eigenmodes of structures with slight deviations from rotational symmetry.  [Show abstract] [Hide abstract]
ABSTRACT: For structures with very fine details or slight geometrical deviations, an approach fully based on discretization frequently causes problem dimensions which are much too big even for powerful computing hardware, In this paper, two such situations are studied: 1.) simulation of an entire 9cell TESLA cavity, fully equipped with HOM and Inputcouplers, the latter demanding for 3Dcomputation; 2.) chains of cavity cells being slightly elliptically deformed with different axis orientation. Both simulations were performed using a scheme which we denote as CoupledSParameterCalculation (CSC), CSC applies a segmentation in several sections of the entire structure. The scattering properties of every segment need to be computed with field solving codes, resulting in (multidimensional) frequency dependent Smatrices. Then CSC is used both for the concatenation of the Smatrices and  if the whole system is entirely closed  to determine its eigenresonances. In our first example we take profit of the rotational symmetry of the inner part  the TESLA cavity, which therefore can be calculated in 2D, The scattering properties of the couplers at both cavity ends are computed separately. Then the CSC result of the overall system Smatrix is used to derive the Qvalues of each single resonance, The study of dipole modes in deformed cavities uses the ability of CSC to calculate the frequencies and the distribution of waveguide mode amplitudes of eigenmodes. It is shown that the orientation of the fields experiences an angular shift along a chain of cells having elliptical deformations of different orientation, Here several parameter sets were analyzed in order to gain some experience on the phenomenon. In this study we took advantage of the analytical description of the celltocell rotation thus leading to very short cpu times.  [Show abstract] [Hide abstract]
ABSTRACT: Es wird eine Methode zur Berechnung der HochfrequenzEigenschaften komplexer Strukturen vorgestellt. Das Verfahren beruht auf der Zerlegung der Gesamtstruktur in einzelne einfachere Segmente, deren breitbandige SMatrizen mit kommerziellen Programmen berechnet werden. Das Gesamtsystem kann von beliebiger Topologie sein, und die Zahl der die Segmente verkoppelnden Hohlleiter Moden ist nicht begrenzt. Als Ergebnis steht bei offenen Strukturen deren vollständige SMatrix, bei abgeschlossenen deren Resonanzeigenschaften zur Verfügung. Die theoretischen Grundlagen werden beschrieben und die Anwendung mit Beispielen aus dem Gebiet der Teilchenbeschleuniger und zu Eigenschaften schwach elliptisch geformter Resonatoren illustriert. A method called Coupled SParameter Calculation – CSC is described which is used to calculate the rf properties of complex structures, i.e. either their scattering (devices with ports) or their resonance properties. The method is based on the segmentation of the entire system into sections being less complex, the external calculation of the section’s broadband Smatrices, and a combination scheme, which is applicable to any topology and number of modes. The method’s principle is described. Examples from the field of particle accelerator cavities and about the properties of weakly elliptical resonators are given.  [Show abstract] [Hide abstract]
ABSTRACT: Recently a third harmonic structure has been proposed for the injector of the TTFFEL to avoid nonlinear distortions in the longitudinal phase space. This structure consists of four nine cell TESLAlike cavities. For the use of this structure in combination with the TTFFEL it might be interesting to investigate higher order modes (HOM) in the structure and their effect on the beam dynamics. In the 5th dipole passband one mode with a frequency around 9.05 Ghz was found to be almost trapped in the cavity with very small fields in the end cells and the beam pipes. CST MicrowaveStudio® (MWS) and Coupled SParameter Calculation (CSC) have been applied to investigate this frequency range. The CSC method (1) 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 frequencies and field distributions of dipole modes in the frequency range around 9.05 GHz.  [Show abstract] [Hide abstract]
ABSTRACT: This paper starts with a very brief review of FIT on triangular grids. Next, it reports about some recent features in FIT to minimize the geometrical error while keeping the number of grid points as small as possible. Finally, a method is introduced to compute scattering properties and/or resonant fields in complex RF structures by combination of domain decomposition with any available CEM tool. We denote this method as coupled Sparameter calculation. Some examples are presented underlining the power of the methods described.  [Show abstract] [Hide abstract]
ABSTRACT: Large rfstructures are sometimes too complex to be calculated entirely in single simulation runs. Usually, if the structure has open ports, the scattering properties  the socalled Sparameters  are of primary interest. As a matter of fact, they can be derived from scattering properties of parts of the entire structure, which are calculated in the procedure presented here in separate, less expensive simulations. A very compact representation of the underlying theory was found, which is presented in the paper. Furthermore, a Mathematica application called CSC based on this formulation is introduced. CSC calculates the scattering properties of an object, which are a combination of an arbitrary structure of segments with previously calculated Sparameters. To illustrate the use of CSC, three examples are shown: higher order mode (HOM) coupling properties of components of the TESLA Test Facility without and with accelerating cavities and the coupling of polarizations in chains of structures with slight deviations from circular cross sections  [Show abstract] [Hide abstract]
ABSTRACT: Numerical calculation of RFproperties of accelerating structures is typically performed by numerical field solving codes such as MAFIA [1] or Microwave Studio™ [1]. Even if components like cavities are of cylindrical symmetry, full 3D modelling is required in order to consider the effects of poweror HOMcouplers. This implies a numerical effort significantly higher than the separate treatment of parts with and without rotational symmetry. Therefore we have developed a method called Coupled SParameter Calculation (CSC) which is based on a scattering parameter description. It uses Sparameters of the various components and results in the entire structure's scattering properties. The Sparameters of the single components are computed by customary field solving codes utilizing any component's symmetry or repetition of subsections. The authors want to demonstrate the capabilities of CSC reporting results on the effect of different HOMcoupler geometries in the TESLA channel and compare the effects of different cavityand coupler arrangements. From the CSC data the frequencies and the Qfactors of the modes in TESLA cavities are calculated. 
Conference Paper: Calculation of HOMs in TESLAcavities using the coupled Sparameter calculation method
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ABSTRACT: The calculation of electromagnetic fields in accelerating structures is normally done by dedicated numerical solvers such as MAFIA. Even if components like cavities are of cylindrical symmetry, full 3D modelling is required in order to consider the effects of power or HOMcouplers. This implies a numerical effort significantly higher than the separate treatment of parts with and without rotational symmetry. Therefore we have developed a method called coupled Sparameter calculation (CSC) which is based on a scattering parameter description. It uses Sparameters of the components found with field solving codes utilising any component's symmetry or repetition of subsections. In the paper we present a parameter variations within a TESLA9cellcavity with couplers and in a 4cavitychain in order to demonstrate the capabilities of CSC  [Show abstract] [Hide abstract]
ABSTRACT: The TTF free electron laser needs very short bunches to produce selfamplified spontaneous emission. This short bunch length is produced in a magnetic bunch compressor where the trajectories of particles with different energy have different path length in a way that the bunch is longitudinally compressed. As a parasitic effect the wake fields produced by the passing bunch will have the possibility to interact with the bunch itself and cause emittance growth. The high frequency behaviour of the beam pipe in the bunch compressor has to be analysed in order to identify trapped higher order modes (HOM) and to estimate beam distortion. Because of the complexity of the bunch compressor section direct eigenmode calculation is not possible due to lack of available computer power. A technique is presented which allows to compute eigenmodes of rfstructures by using scatteringparameters of subsections of the bunch compressor. This is done numerically based on the computer code MAFIA to model the different sections of the beam pipe 
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ABSTRACT: Large rfstructures are sometimes too complex to be calculated entirely in single simulation runs. If the structure has open ports usually the scattering properties with respect to these ports  the socalled Sparameters  are of primary interest . They can be derived from scattering properties of parts of the entire structure, which may be calculated in separate, less expensive simulations. The paper describes briefly the underlying theory and introduces a Mathematica™ application called CSC, that calculates the scattering properties of an object which is a combination of an arbitrary structure of segments with previously calculated S parameters. For users who are not familiar with Mathematica, a short introduction is given. The commands available in the CSC package are explained and an example is illustrated in detail.
Publication Stats
17  Citations  
1.39  Total Impact Points  
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Institutions

20012011

University of Rostock
 • Institut für Allgemeine Elektrotechnik
 • Institute of Electrical Power Engineering
Rostock, MecklenburgVorpommern, Germany
