Author: Lasheen, A.
Paper Title Page
MOP13 Influence of Transverse Motion on Longitudinal Space Charge in the CERN PS 83
 
  • A.J. Laut, A. Lasheen
    CERN, Geneva 23, Switzerland
 
  Particles in an intense bunch experience longitudinal self-fields due to space~charge. This effect, conveniently described by geometric factors dependent on a particle’s transverse position, beam size, and beam pipe aperture, is usually incorporated into longitudinal particle tracking on a per-turn basis. The influence of transverse betatron motion on longitudinal space~charge forces is, however, usually neglected in pure longitudinal tracking codes. A dedicated tracking code was developed to characterize the CERN PS such that an effective geometric factor of a given particle could be derived from its transverse emittance, betatron phase~advance, and momentum~spread. The effective geometry factor is then estimated per particle by interpolation without the need for full transverse tracking and incorporated into the longitudinal tracker BLonD. The paper evaluates this effect under conditions representative of the PS, where space~charge is dominant at low energy and progressively becomes negligible along the acceleration ramp. The synchrotron frequency distribution is modified and the filamentation rate is moreover increased, which could suggest a stabilizing space~charge phenomenon.  
poster icon Poster MOP13 [1.826 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-HB2021-MOP13  
About • Received ※ 16 October 2021 — Revised ※ 22 October 2021 — Accepted ※ 12 December 2021 — Issue date ※ 11 April 2022
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MOP17 End-to-End Longitudinal Simulations in the CERN PS 106
 
  • A. Lasheen, H. Damerau, K. Iliakis
    CERN, Geneva, Switzerland
 
  In the context of the LHC Injector Upgrade (LIU) project, the main longitudinal limitations in the CERN PS are coupled bunch instabilities and uncontrolled emittance blow-up leading to losses at injection into the downstream accelerator, the SPS. To complement beam measurements, particle tracking simulations are an important tool to study these limitations. However, to avoid excessive runtime, simulations are usually targeting only a fraction of the cycle assuming that bunches are initially matched to the RF bucket. This ignores all initial perturbations that could seed an instability. Simulations were therefore performed along the full PS cycle by using the BLonD tracking code optimized with advanced parallelization schemes. They include beam manipulations with several RF harmonics (batch compression, merging, splittings), controlled emittance blow-up, a model of the beam coupling impedance covering a wide frequency range, as well as beam and cavity feedbacks. A large number of macroparticles is required as well as arrays to store beam induced voltage spanning several revolutions to account for long range wakefields.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-HB2021-MOP17  
About • Received ※ 16 October 2021 — Revised ※ 19 October 2021 — Accepted ※ 01 April 2022 — Issue date ※ 11 April 2022
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