Keyword: HOM
Paper Title Other Keywords Page
WEP07 Traveling Poles Elimination Scheme and Calculations of External Quality Factors of HOMs in SC Cavities cavity, simulation, factory, linac 152
 
  • T. Galek, T. Flisgen, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • A. Neumann
    HZB, Berlin, Germany
  • B. Riemann
    DELTA, Dortmund, Germany
 
  Funding: Funded by EU FP7 Research Infrastructure Grant No. 227579 and funding approved by German Federal Ministry of Research & Education, Project: 05K10HRC
The main scope of this work is the automation of the extraction procedure of the external quality factors Qext of Higher Order Modes (HOMs) in Superconducting (SC) radio frequency cavities [*]. The HOMs are generated by charged particle beams traveling at the speed of light through SC cavity. The HOMs decay very slowly, depending on localization inside the structure and cell-to-cell coupling, and may influence succeeding charged particle bunches. Thus it is important, at the SC cavity design optimization stage, to calculate the Qext of HOMs. The Traveling Poles Elimination (TPE) scheme has been used on scattering parameters spectra to obtain external quality factors. The combination of Coupled S-Parameter Calculations (CSC) method and vector fitting procedure allows us to study very complicated structures in much better details and almost automated extraction of HOMs' Qext factors. The results are also reasserted by careful eigenmode analysis of the SC cavity. The S-Parameter and eigenmode simulations were performed using CST Microwave Studio.
*Axel Neumann et al., "Status of the HOM Calculations for the BERLinPro Main Linac Cavity", FRAAC3 (this conference)
 
 
WEP14 Design of SRF Cavities with Cell Profiles Based on Bezier Splines cavity, linac, SRF, coupling 167
 
  • B. Riemann, T. Weis
    DELTA, Dortmund, Germany
  • A. Neumann
    HZB, Berlin, Germany
 
  Funding: This work is funded by BMBF under contract 05K10PEA.
Elliptical cavities have been a standard in SRF linac technology for 30 years. In this work, we present a novel approach [1] using Bezier spline profile curves. By using different degrees of spline curves, the number of free parameters can be varied to suit a given problem (endcell tuning, basecell figures of merit), thus leading to a high flexibility of the spline approach. As a realistic example, a cubic spline SRF multicell cavity geometry is calculated and the figures of merit are optimized for the operational mode. We also present an outline for HOM endcell optimization that can be realized using available 2D solvers.
[1] B. Riemann et al., "SRF multicell cavity design using cubic and higher order spline cavity profiles", T 80.9, Verhandlungen DPG Göttingen 2012
 
 
THP06 An OpenMP Parallelisation of Real-time Processing of CERN LHC Beam Position Monitor Data controls, target, insertion, non-linear-dynamics 230
 
  • H. Renshall, L. Deniau
    CERN, Geneva, Switzerland
 
  SUSSIX is a FORTRAN program for the post processing of turn-by-turn Beam Position Monitor (BPM) data, which computes the frequency, amplitude, and phase of tunes and resonant lines to a high degree of precision. For analysis of LHC BPM data a specific version run through a C steering code has been implemented in the CERN Control Centre to run on a server under the Linux operating system but became a real time computational bottleneck preventing truly on-line study of the BPM data. Timing studies showed that the independent processing of each BPMs data was a candidate for parallelization and the OpenMP package with its simple insertion of compiler directives was tried. It proved to be easy to learn and use, problem free and efficient in this case reaching a factor of ten reduction in real-time over twelve cores on a dedicated server. This paper reviews the problem, shows the critical code fragments with their OpenMP directives and the results obtained.  
 
THACI1 Lumped Equivalent Models of Complex RF Structures impedance, RF-structure, scattering, factory 245
 
  • T. Flisgen, J. Heller, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
 
  Funding: partly funded by EU FP7 Research Infrastructure Grant No. 227579
The prediction of RF properties of complex accelerating structures is an important issue in computational accelerator physics. This paper describes the derivation of state space equations for complex structures based on real eigenmodes of sections of the decomposed complex structure. The state space equations enable the calculation of system responses due to port excitations by means of standard ordinary differential equation solvers. Therefore, the state space equations are referred to as lumped equivalent models of such complex RF structures. Besides fast computation of system responses, the equivalent models enable the calculation of secondary quantities such as external quality factors. The present contribution discusses theoretical aspects and illustrates an application example.
 
slides icon Slides THACI1 [1.538 MB]  
 
FRAAI1 Computational Needs for RF Design of Superconducting Cavities cavity, simulation, SRF, linac 270
 
  • A. Lunin, T.N. Khabiboulline, V.P. Yakovlev
    Fermilab, Batavia, USA
 
  Funding: Operated by Fermi Research Alliance, LLC under Contract No.DE-AC02-07CH11359 with the U.S. Department of Energy.
The computational approaches assure essential guidance and order for the design of a superconducting cavities and cryomodules. The nature of superconductivity requires precise surface electromagnetic fields computation in order to design the cavity shape with a maximum accelerating gradient. At the same time the thickness of the cavity shell is limited by the ability to cool it down the temperature of liquid He, which makes the mechanical stability of the cavity and liquid He vessel assembly extremely important. Hence, it demands a self consistent electro-mechanical optimization in order to minimize microphonics and/or Lorentz force detuning phenomena. Specific challenges are an estimation of RF losses caused by the interaction of the passing beam with SC cavity and a multipactor analysis in the SC cavity and RF coupler. Finally the irregular time structure of a beam train with its own dense spectra may stochastically induce HOM fields in a cavity which results the beam emittance dilution. The study of these effects leads to specifications of SC cavity and cryomodule and can significantly impact on the efficiency and reliability of the superconducting linac operation.
 
slides icon Slides FRAAI1 [8.162 MB]  
 
FRAAC3 Status of the HOM Calculations for the BERLinPro Main Linac Cavity cavity, dipole, linac, quadrupole 278
 
  • A. Neumann, W. Anders, J. Knobloch
    HZB, Berlin, Germany
  • K. Brackebusch, T. Flisgen, T. Galek, K. Papke, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • B. Riemann, T. Weis
    DELTA, Dortmund, Germany
 
  Funding: Work supported by Federal Ministry for Research and Education BMBF under contract 05K10HRC
The Berlin Energy Recovery Linac Project (BERLinPro) is designed to develop and demonstrate CW LINAC technology and expertise required to drive next-generation Energy Recovery Linacs (ERLs). Strongly higher order mode (HOM) damped multicell 1.3 GHz cavities are required for the main linac. The cavity under study is an integrated design of the Cornell base cell with JLab HOM waveguide couplers. Modifications to the end group design have also been pursued, including the substitution of one waveguide by a HZB-modified TTF-III power coupler. In this talk the progress in HOM calculations to avoid beam-breakup instabilities for the favored cavity structure will be presented.
 
slides icon Slides FRAAC3 [15.439 MB]