T. Weiland

Technical University Darmstadt, Darmstadt, Hesse, Germany

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Publications (645)504.46 Total impact

  • Yves Hackl · Peter Scholz · Wolfgang Ackermann · Thomas Weiland ·
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    ABSTRACT: This paper focuses on two special aspects regarding fast partial inductance computations in the nonorthogonal partial element equivalent circuit (PEEC) method. First, a multifunction PEEC algorithm is proposed, which is able to calculate partial inductances as efficient as possible for mixed environments with nonorthogonal as well as orthogonal cells. Second, a new numerical integration routine for the self-inductance terms of nonorthogonal cells is focused on by using averaged orthogonal subelements. It is presented that the slow convergence caused by the singularities is avoided and a fast evaluation of the self-terms is enabled consequently. The approach is verified by two examples where a good agreement is obtained when comparing the proposed results with analytical solutions as well as finite-element method reference results.
    IEEE Transactions on Electromagnetic Compatibility 10/2015; 57(5):1-9. DOI:10.1109/TEMC.2015.2433018 · 1.30 Impact Factor

  • 20th International Conference on the Computation of Electromagnetic fields, COMPUMAG 15, Montreal, Quebeck; 06/2015

  • 20th International Conference on the Computation of Electromagnetic fields, COMPUMAG '15, Montreal, Quebeck; 06/2015

  • 6th International Particle Accelerator Conference (IPAC 2015), Richmond, Virginia, USA; 05/2015
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    6th International Particle Accelerator Conference (IPAC 2015), Richmond, Virginia, USA,; 05/2015
  • Hideki Kawaguchi · Seiya Itasaka · Thomas Weiland ·
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    ABSTRACT: A time-domain boundary element method (TDBEM) provides one more possibility of potential numerical schemes for a time domain microwave simulation in addition to the finite difference time domain method. However, it is known that the TDBEM requires very large memory of order of 100 GB. As one of the solutions to effective memory reduction, this paper presents a 4-D domain decomposition method for the TDBEM. It is shown that the 4-D domain decomposition method of the TDBEM works well for the effective memory reduction in a particle accelerator wake field analysis.
    IEEE Transactions on Magnetics 03/2015; 51(3):1-4. DOI:10.1109/TMAG.2014.2361613 · 1.39 Impact Factor
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    ABSTRACT: This paper proposes the extraction of surrogate field models from 3-D electromagnetic simulation results, for use in a Vlasov beam-dynamics code. Each accelerator component is represented by a dedicated surrogate field model based on a series expansion of its 3-D field distribution. The obtained beam-dynamics simulation results are validated against a particle-in-cell tracking code that integrates a 3-D field distribution of the corresponding accelerator component.
    IEEE Transactions on Magnetics 03/2015; 51(3):1-4. DOI:10.1109/TMAG.2014.2357027 · 1.39 Impact Factor
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    ABSTRACT: An evaluation of the cone-shaped pickup performance as a part of the high bandwidth bunch arrival-time monitors (BAMs) for a low charge sub-10 fs arrival-time measurements is presented. Three sets of pickups are installed at the free electron laser FLASH at Deutsches Elektronen-Synchrotron, the quasi-cw SRF accelerator ELBE at the Helmholtz-Zentrum Dresden-Rossendorf and the SwissFEL injector test facility at Paul Scherrer Institute. Measurements and simulations are in good agreement and the pickups fulfill the design specifications. Utilizing the high bandwidth BAM with the cone-shaped pickups, an improvement of the signal slope by a factor of 10 is demonstrated at ELBE compared to the BAM with a low bandwidth.
    Physical Review Special Topics - Accelerators and Beams 01/2015; 18(1). DOI:10.1103/PhysRevSTAB.18.012801 · 1.66 Impact Factor
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    ABSTRACT: Measurements of the magnetic characteristics of the Ferroxcube 8C12m ferrite material in the parameter range where the GSI heavy-ion synchrotron SIS 18 cavity resonator is operated are presented. At first, the permeability is determined as a function of frequency and bias magnetic field strength for low radio-frequency power levels. For this purpose, both reflection and transmission measurements are carried out in a test setup with two toroids. The values for the real and imaginary part obtained from the data analysis of both approaches are fully in agreement with each other, albeit the range of application of the latter setup is limited to moderate frequencies due to parasitic resonances. An empirical analytical expression is formulated which approximates the complex permeability reasonably well in the whole investigated bias and frequency range. Moreover, the $B$-$H$ curve is recorded for a reduced bias current range of the cavity. The gained material characteristics are well suited for numerical eigenmode simulations for the GSI SIS 18 cavity.
    Physical Review Special Topics - Accelerators and Beams 01/2015; 18(1). DOI:10.1103/PhysRevSTAB.18.010101 · 1.66 Impact Factor
  • Klaus Klopfer · Wolfgang Ackermann · Thomas Weiland ·
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    ABSTRACT: Explicit expressions for the permittivity and inverse permeability tensor for gyrotropic materials are derived for the finite integration technique (FIT) in frequency domain. In contrast to the standard FIT, the material matrices exhibit nondiagonal elements. The obtained expressions are fully consistent with the standard FIT when applied to nongyrotropic materials. Furthermore, the manifestly Hermitian matrix structure in the lossless case enables numerically stable simulations. Since the gyrotropic characteristics notably depend on the bias magnetic field and on the frequency of the superimposed field, a dedicated solver to determine the field distributions in practical applications has been developed. In particular, emphasis has been put on the implementation to enable efficient computing. Finally, the extended formulation is applied to the computation of eigenmodes of biased cavity resonators of cylindrical and rectangular shape, which are filled with material exhibiting both gyromagnetic and gyroelectric characteristics. For the latter resonator, material losses are included. The validity of numerically obtained results is confirmed by comparison with semianalytical calculations.
    IEEE Transactions on Magnetics 01/2015; 51(1):1-7. DOI:10.1109/TMAG.2014.2338275 · 1.39 Impact Factor

  • IEEE Transactions on Magnetics 01/2015; DOI:10.1109/TMAG.2015.2490547 · 1.39 Impact Factor
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    ABSTRACT: We consider the discretization of electromagnetic wave propagation problems by a discontinuous Galerkin Method based on Trefftz polynomials. This method fits into an abstract framework for space-time discontinuous Galerkin methods for which we can prove consistency, stability, and energy dissipation without the need to completely specify the approximation spaces in detail. Any method of such a general form results in an implicit time-stepping scheme with some basic stability properties. For the local approximation on each space-time element, we then consider Trefftz polynomials, i.e., the subspace of polynomials that satisfy Maxwell's equations exactly on the respective element. We present an explicit construction of a basis for the local Trefftz spaces in two and three dimensions and summarize some of their basic properties. Using local properties of the Trefftz polynomials, we can establish the well-posedness of the resulting discontinuous Galerkin Trefftz method. Consistency, stability, and energy dissipation then follow immediately from the results about the abstract framework. The method proposed in this paper therefore shares many of the advantages of more standard discontinuous Galerkin methods, while at the same time, it yields a substantial reduction in the number of degrees of freedom and the cost for assembling. These benefits and the spectral convergence of the scheme are demonstrated in numerical tests.
    SIAM Journal on Scientific Computing 12/2014; 37(5). DOI:10.1137/140999323 · 1.85 Impact Factor
  • K. Bavelis · E. Gjonaj · T. Weiland ·
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    ABSTRACT: The electrical transport in zinc oxide (ZnO) varistors is analyzed using microstructural material modeling. The fully three dimensional current distribution is computed by means of a nonlinear equivalent circuit model representing the assembly of current carrying grains and grain boundaries of the material. The investigation focuses on the phenomenon of current filamentation due to inhomogeneities of the varistor microstructure. Numerical results highlight the importance of 3-D percolation effects in the modeling of varistor currents as well as that of the grain bulk resistivity which so far has been neglected in previous studies.
    Advances in Radio Science 11/2014; 12:29-34. DOI:10.5194/ars-12-29-2014
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    ABSTRACT: The modeling and simulation of electromagnetic wave propagations is often acompanied by a restriction to bounded domains and the introduction of artificial boundary conditions which should be chosen in order to minimize parasitic reflections. In this paper, we investigate a new type of transparent boundary condition and its implementation in a Discontinuous Galerkin Trefftz Finite Element Method. The choice of a particular set of basis functions allows us to split the electromagnetic field into components with a specified direction of propagation. The reflections at the artificial boundaries are then reduced by penalizing components of the field incoming into the space-time domain of interest. We formally introduce this concept, discuss its realization within the discontinuous Galerkin framework, and demonstrate the performance of the resulting approximations in comparison with commonly used absorbing boundary conditions. In our numerical tests, we observe spectral convergence in the L2 norm and a dissipative behaviour for which we provide a theoretical explanation.
    Applied Mathematics and Computation 10/2014; 267. DOI:10.1016/j.amc.2015.06.026 · 1.55 Impact Factor
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    ABSTRACT: Quadrupolar or beam envelope oscillations give valuable information about the injection matching and the incoherent space charge tune shift. An asymmetric capacitive pick-up was installed at GSI SIS-18 to measure these oscillations. In this contribution, we present the simulations performed to es-timate the sensitivity of the quadrupolar pick-up to the beam quadrupolar moment and compare it with respect to other pick-up types installed at SIS-18. Further, dedicated beam measurements are performed to interpret the quadrupolar signal under high intensity conditions.
    IBIC 2014; 09/2014
  • Irene Woyna · Erion Gjonaj · Thomas Weiland ·
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    ABSTRACT: Purpose - The purpose of this paper is to present a time domain discontinuous Galerkin (DG) approach for modeling wideband frequency dependent surface impedance boundary conditions. Design/methodology/approach - The paper solves the Maxwellian initial value problem in a computational domain, which is spatially discretized by the higher order DG method. On the boundary of the computational domain the paper applies a suitable impedance boundary condition (IBC). The frequency dependency of the impedance function is modeled by auxiliary differential equations (ADE). Findings - The authors will study the resonance frequency and the Q factor of different types of cavity resonators including lossy materials. The lossy materials are modeled by means of IBCs. The authors will compare the results with analytical results, as well as numerical results obtained by direct calculations where lossy materials are included explicitly into the numerical model. Several convergence studies are performed which demonstrate the accuracy of the approach. Originality/value - Modeling of frequency dependent boundary conditions in time domain with finite difference time domain method (FDTD) method is considered in numerous papers, as well as in frequency domain finite element method (FEM), and in a few papers also time domain FEM. However, FDTD method is only first order accurate and fails in modeling of complicated surfaces. FEM allows for high order accuracy, but time domain modeling is numerically extremely expensive. In frequency domain, broadband modeling of frequency dependent boundary conditions requires several simulations as opposed to the time domain, where a single simulation is needed. The time domain DG method proposed in this paper allows to overcome the difficulties. The authors introduce a broadband surface impedance formulation based on the ADE approach for the higher order DG method.
    COMPEL International Journal of Computations and Mathematics in Electrical 07/2014; 33(4):1082-1096. DOI:10.1108/COMPEL-08-2013-0260 · 0.37 Impact Factor
  • Y. C h e n · E. Gjonaj · W.F.O. Müller · T. Weiland ·

    International Particle Accelerator Conference 2014, Dresden, Germany; 06/2014
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  • Hideki Kawaguchi · Seiya Itasaka · Thomas Weiland ·
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    ABSTRACT: A time domain boundary element method (TDBEM) gives us another possibility of time domain microwave simulations in addition to a finite difference time domain (FDTD) method. In particular, the TDBEM has good advantages in analysis of coupling problems with charged particle motion such as in a particle accelerator. However, it is known that time domain microwave simulations in the particle accelerator by the conventional TDBEM often encounter numerical instability and inaccuracy because of its bad matrix property. To avoid the numerical instability and inaccuracy caused by the conventional open boundary problem formulation of the TDBEM, an initial value problem formulation of 3-D TDBEM is presented in this paper.
    IEEE Transactions on Magnetics 02/2014; 50(2):593-596. DOI:10.1109/TMAG.2013.2281057 · 1.39 Impact Factor
  • Todorka Banova · Wolfgang Ackermann · Thomas Weiland ·
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    ABSTRACT: In this paper, we address a fast approach for an accurate eigenfrequency determination, based on a finite-element computation of electromagnetic fields for a superconducting cavity and further employment of the Lanczos method for the eigenvalue determination. The major challenges posed by this paper are: 1) the ability of the approach to tackle the large-scale eigenvalue problem and 2) the capability to extract many, i.e., order of thousands, eigenfrequencies for the considered problem. In addition to the need to ensure high precision of the calculated eigenfrequencies, we compare them side by side with the reference data available from analytical expressions and CEM3D eigenmode solver. Furthermore, the simulations have shown high accuracy of this technique and good agreement with the reference data. Finally, all of the results show that the suggested technique can be used for precise determination of many eigenfrequencies.
    IEEE Transactions on Magnetics 02/2014; 50(2):481-484. DOI:10.1109/TMAG.2013.2283917 · 1.39 Impact Factor

Publication Stats

5k Citations
504.46 Total Impact Points


  • 1994-2015
    • Technical University Darmstadt
      • • Insitute of Computational Electromagnetics
      • • Institute of Nuclear Physics
      Darmstadt, Hesse, Germany
  • 1996-2012
    • Stanford University
      • SLAC National Accelerator Laboratory
      Palo Alto, California, United States
  • 2010
    • GSI Helmholtzzentrum für Schwerionenforschung
      • ExtreMe Matter Institute EMMI and Research Division
      Darmstadt, Hesse, Germany
  • 2008
    • Argonne National Laboratory
      Lemont, Illinois, United States
  • 1982-2006
    • Darmstadt University of Applied Sciences
      Darmstadt, Hesse, Germany
  • 2001
    • CST – Computer Simulation Technology AG
      Darmstadt, Hesse, Germany
  • 1998
    • University of Rostock
      Rostock, Mecklenburg-Vorpommern, Germany
  • 1984-1992
    • Deutsches Elektronen-Synchrotron
      Hamburg, Hamburg, Germany
  • 1981
    • CERN
      Genève, Geneva, Switzerland