Keyword: coupling
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SAPAG04 HOM-Mitigation for Future SPS 33-Cell 200 MHz Accelerating Structures HOM, damping, impedance, cavity 35
  • P. Kramer, C. Vollinger
    CERN, Geneva, Switzerland
  The CERN SPS 200 MHz travelling wave (TW) accelerating structures pose an intensity limitation for the planned High Luminosity (HL-) LHC upgrade. Higher-order modes (HOMs) around 630 MHz have been identified as one of the main sources of longitudinal multi-bunch instabilities. Improved mitigation of these HOMs with respect to today’s HOM-damping scheme is therefore an essential part of the LHC injectors upgrade (LIU) project. The basic principles of HOM-couplers in cavities and today’s damping scheme are reviewed, before illustrating the numerous requirements an improved damping scheme for the future 33-cell structures must fulfil. These are, amongst others, the mitigation of HOMs situated in the lower part of the structure where there are no access ports for extraction, a sufficient overall damping performance and an acceptable influence on the fundamental accelerating passband (FPB). Different approaches tackling these challenges are investigated and their performance, advantages and pitfalls are evaluated by ACE3P and CST electromagnetic (EM) field solver suites.  
slides icon Slides SAPAG04 [2.184 MB]  
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About • paper received ※ 19 October 2018       paper accepted ※ 24 October 2018       issue date ※ 26 January 2019  
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SUPAG01 Space Charge and Transverse Instabilities at the CERN SPS and LHC simulation, optics, space-charge, impedance 80
  • E. Métral, D. Amorim, G. Arduini, H. Bartosik, E. Benedetto, H. Burkhardt, K.S.B. Li, A. Oeftiger, D. Quatraro, G. Rumolo, B. Salvant, C. Zannini
    CERN, Geneva, Switzerland
  At the CERN accelerator complex, it seems that only the highest energy machine in the sequence, the LHC, with space charge (SC) parameter close to one, sees the predicted beneficial effect of SC on transverse coherent instabilities. In the other circular machines of the LHC injector chain (PSB, PS and SPS), where the SC parameter is much bigger than one, SC does not seem to play a major (stabilising) role, and it is maybe the opposite in the SPS. All the measurements and simulations performed so far in both the SPS and LHC will be reviewed and analysed in detail.  
slides icon Slides SUPAG01 [37.523 MB]  
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About • paper received ※ 20 October 2018       paper accepted ※ 19 November 2018       issue date ※ 26 January 2019  
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MOPAF04 Spin Dynamics in Modern Electron Storage Rings: Computational Aspects polarization, electron, storage-ring, radiation 146
  • O. Beznosov, J.A. Ellison, K.A. Heinemann
    UNM, Albuquerque, New Mexico, USA
  • D. Appelö
    University of Colorado at Boulder, Boulder, USA
  • D.P. Barber
    DESY, Hamburg, Germany
  Funding: This material is based on work supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, under Award Number DE-SC0018008.
In this talk we present some numerical results from our work on the spin polarization in high energy electron storage rings. The motivation of our work is to understand spin polarization in very high energy rings like the proposed Future Circular Collider* (FCC-ee) and Circular Electron Positron Collider** (CEPC). This talk is a supplement to K. Heinemann’s talk and gives further numerical details and results. As discussed in Heinemann’s talk our work is based on the initial value problem of the full Bloch equations*** (FBEs) which in turn determines the polarization vector of the bunch. The FBEs take into account spin diffusion effects and spin-flip effects due to synchrotron radiation. The FBEs are a system of three uncoupled Fokker-Planck equations plus coupling terms. Neglecting the spin flip terms in the FBEs one gets the reduced Bloch equations (RBEs) which poses the main computational challenge. Our numerical approach has three parts. Firstly we approximate the FBEs analytically using the method of averaging, resulting in FBEs which allow us to use large time steps (without the averaging the time dependent coefficients of the FBEs would necessitate small time steps). The minimum length of the time interval of interest is of the order of the orbital damping time. Secondly we discretize the averaged FBEs in the phase space variables by applying the pseudospectral method, resulting in a system of linear first-order ODEs in time. The phase space variables come in d pairs of polar coordinates where d = 1, 2, 3 is the number of degrees of freedom allowing for a d-dimensional Fourier expansion. The pseudospectral method is applied by using a Chebychev grid for each radial variable and a uniform Fourier grid for each angle variable. Thirdly we discretize the ODE system by a time stepping scheme. The presence of parabolic terms in the FBEs necessitates implicit time stepping and thus solutions of linear systems of equations. Dealing with 2d + 1 independent variables p
* See
** See
*** See
slides icon Slides MOPAF04 [0.993 MB]  
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About • paper received ※ 20 October 2018       paper accepted ※ 24 October 2018       issue date ※ 26 January 2019  
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TUPAF01 Upgrade of MAD-X for HL-LHC Project and FCC Studies radiation, synchrotron, synchrotron-radiation, lattice 165
  • L. Deniau, H. Burkhardt, R. De Maria, M. Giovannozzi, J.M. Jowett, A. Latina, T. Persson, F. Schmidt, I.S. Shreyber, P.K. Skowroński
    CERN, Geneva, Switzerland
  • T.G. Gläßle
    HIT, Heidelberg, Germany
  The design efforts for the High Luminosity upgrade of the Large Hadron Collider (HL-LHC) and for the FCC-ee project required significant extensions of the MAD-X code widely used for designing and simulating particle accelerators. The modelling of synchrotron radiation effects has recently been reviewed, improved and tested on the lattices of ESRF, LEP and CLIC Final Focus System. The results were cross checked with the codes AT, PLACET, Geant4, and MAD8. The implementation of space charge has been drastically restructured in a modular design. The linear coupling calculation has been completely reviewed and improved, from the theory to the implementation in MAD-X code to ensure its correctness in the presence of strong coupling as in the HL-LHC studies. The slicing module has been generalised to allow for thick slices of bending magnets, quadrupoles and solenoids. The SBEND element has been extended to support difference between bending angle and integrated dipole strength. Patches have been added to the list of supported elements. MAD-X PTC has also been extended to track resonance driving terms along layouts, and to support AC dipoles to simulate beams during optics measurements.  
slides icon Slides TUPAF01 [5.986 MB]  
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About • paper received ※ 17 October 2018       paper accepted ※ 24 October 2018       issue date ※ 26 January 2019  
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TUPAG01 Computation of Eigenmodes in the BESSY VSR Cavity Chain by Means of Concatenation Strategies cavity, impedance, GUI, factory 253
  • T. Flisgen, A.V. Vélez
    HZB, Berlin, Germany
  • J. Heller, G. Zadeh, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  Funding: The research leading to these results was supported by the German Bundesministerium für Bildungund Forschung, Land Berlin and grants of Helmholtz Association
Invited Talk: The computation of eigenmodes in chains of superconducting cavities with asymmetric couplers is a demanding problem. This problem typically requires the use of high-performance computers in combination with dedicated software packages. Alternatively, the eigenmodes of chains of superconducting cavities can be determined by the so-called State-Space Concatenation (SSC) approach that has been developed at the University of Rostock. SSC is based on the decomposition of the full chain into individual segments. Subsequently, the RF properties of every segment are described by reduced-order models. These reduced-order models are concatenated to a reduced-order model of the entire chain by means of algebraic side constraints arising from continuity conditions of the fields across the decomposition planes. The constructed reduced-order model describes the RF properties of the complete structure so that the field distributions, the coupling impedances and the external quality factors of the eigenmodes of the full cavity chain are available. In contrast to direct methods, SSC allows for the computation of the eigenmodes of cavity chains using desktop computers. The current contribution revises the scheme using the BESSY VSR cavity chain as an example. In addition, a comparison between a direct computation of a specific localized mode is described.
slides icon Slides TUPAG01 [3.483 MB]  
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About • paper received ※ 21 October 2018       paper accepted ※ 28 January 2019       issue date ※ 26 January 2019  
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