Author: Baumgarten, C.
Paper Title Page
WEB03 Factors Influencing the Vortex Effect in High-Intensity Cyclotrons 270
 
  • C. Baumgarten
    PSI, Villigen PSI, Switzerland
 
  We discuss factors that have potential influence on the space charge induced vortex motion of particles within high intensity bunches (curling of bunches, Gordon 1969) in isochronous cyclotrons. The influence of the phase slip due to deviations from strict isochronism determines if the bunches of a specific turn are above, below or at "transition", and hence whether stable vortex motion of the bunches is possible at all. Secondly there are possible longitudinal and transverse effects of rf acceleration, the former depending on the bunch phase ("bunching" or "debunching"), the latter depending on the gradient of the accelerating voltage. High accelerating voltages in the first turns call the applicability of adiabatic approximations and analytic methods into question. The influence of the rf acceleration is expected to be significant only at low beam energy, i.e. should have small or even negligible effect beyond the central region of compact machines.  
slides icon Slides WEB03 [1.145 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-Cyclotrons2019-WEB03  
About • paper received ※ 16 September 2019       paper accepted ※ 26 September 2019       issue date ※ 20 June 2020  
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THA01 Precise Modelling and Large Scale Multiobjective Optimisation of Cyclotrons 284
 
  • J. Snuverink, A. Adelmann, C. Baumgarten, M. Frey
    PSI, Villigen PSI, Switzerland
 
  The usage of numerical models to study the evolution of particle beams is an essential step in the design process of particle accelerators. However, uncertainties of input quantities such as beam energy and magnetic field lead to simulation results that do not fully agree with measurements. Hence the machine will behave differently compared to the simulations. In case of cyclotrons such discrepancies affect the overall turn pattern or alter the number of turns. Inaccuracies at the PSI Ring cyclotron that may harm the isochronicity are compensated by 18 trim coils. Trim coils are often absent in simulations or their implementation is simplistic. A realistic trim coil model within the simulation framework OPAL is presented. It was used to match the turn pattern of the PSI Ring. Due to the high-dimensional search space consisting of 48 simulation input parameters and 182 objectives (i.e. turns) simulation and measurement cannot be matched in a straightforward manner. Instead, an evolutionary multi-objective optimisation with more than 8000 simulations per iteration together with a local search approach was applied that reduced the maximum error to 4.5 mm over all 182 turns.  
slides icon Slides THA01 [6.834 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-Cyclotrons2019-THA01  
About • paper received ※ 25 September 2019       paper accepted ※ 27 September 2019       issue date ※ 20 June 2020  
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