BLonD code development meeting



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BLonD code development meeting
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Helga Timko
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Review of BLonD manuscript

  • In 2 weeks' time: finish your own part of the manuscript

  • In 4 weeks' time: review entire manuscript and leave your comments to others

Ivan: Faster induced-voltage calculation 

  • Application: FCC with large circumference, 10000s of bunches
    • 10 B macro particles needed if scaling directly
    • Transverse feedback studies done in 2018 with PyHEADTAIL
  • Present BLonD implementations
    • Freq domain: circular convolution -> periodic result, any impedance model; uniform sampling needed
    • Time domain: linear convolution with zero padding, any impedance model; uniform sampling needed
    • Resonator impedance: matrix multiplication -> non-uniform sampling needed, but N^2 complexity
    • Ideally, want to have non-uniform implementation, but with Nlog(N) complexity
  • Compressed convolution by ABP
    • Drawback: double number of slices needed
    • For multi-turn wake, empty bucket sampling needed
  • How does it work?
    • Induced voltage only needed on the points where the line density is not zero
    • Introducing a MASKING of the data -> can cut the wakefield data
    • Calculate convolution on compressed data
      • For the relevant bins, the results are the same
      • For other locations, data is not correct => CANNOT use it for beam with LOSSES
  • Performance test:
    • Full convolution with 5 bucket bunch spacing vs. full conv with 15 bucket bunch spacing vs compressed convolution: compressed convolution performs best of all
    • The smaller the spacing, the less the improvement
  • Remarks on wake calculation
    • N. Mounet: exact analytical wake calculation can be approximated by cubic Hermitian interpolation
      • example: resistive wall impedance is not correctly represented by standard FFT, while analytical approximation is correct
    • Drawback: analytical expression of the impedance needed
      • For cases where the impedance is known, but wake cannot be calculated
  • Implementation in BLonD: Ivan will make a first implementation
    • Already existing SparseSlicing objects
      • Issue reported by Markus in C++ implementation
  • Mihaly: how about using non-uniform FFT?
There are minutes attached to this event. Show them.
    • 10:30 11:00
      News 30m
      • progress with BLonD paper
      Speakers: Alexandre Lasheen (CERN) , Giulia Papotti (CERN) , Heiko Damerau (CERN) , Ivan Karpov (CERN) , Konstantinos Iliakis (CERN) , Luis Eduardo Medina Medrano (CERN) , Markus Schwarz (KIT) , Panagiotis Tsapatsaris (NTUA) , Simon Albright (CERN) , Theodoros Argyropoulos (CERN)
    • 11:00 11:20
      Faster induced-voltage calculation 20m
      Speaker: Ivan Karpov (CERN)