Keyword: dipole
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SUPAG03 Challenges in Extracting Pseudo-Multipoles From Magnetic Measurements multipole, induction, experiment, quadrupole 87
 
  • S. Russenschuck, G. Caiafa, L. Fiscarelli, M. Liebsch, C. Petrone, P. Rogacki
    CERN, Geneva, Switzerland
  
  Ex­tract­ing the co­ef­fi­cients of Fourier-Bessel se­ries, known as pseudo-mul­ti­poles or gen­er­al­ized gra­di­ents, from mag­netic mea­sure­ments of ac­cel­er­a­tor mag­nets in­volves tech­ni­cal and math­e­mat­i­cal chal­lenges. First, a novel de­sign of a short, ro­tat­ing-coil mag­ne­tome­ter is re­quired that does not in­ter­cept any axial field com­po­nent of the mag­net. More­over, dis­plac­ing short mag­ne­tome­ters, step-by-step along the mag­net axis, yields a con­vo­lu­tion of the local mul­ti­pole field er­rors and the sen­si­tiv­ity (test func­tion) of the in­duc­tion coil. The de­con­vo­lu­tion must then con­tent with the low sig­nal-to-noise ratio of the mea­sur­ands, which are in­te­grated volt­ages cor­re­spond­ing to spa­tial flux dis­tri­b­u­tions. Fi­nally, the com­pen­sa­tion schemes, as im­ple­mented on long coils used for mea­sur­ing the in­te­grated field har­mon­ics, can­not be ap­plied to short mag­ne­tome­ters. All this re­quires care­ful de­sign of ex­per­i­ment to de­rive the op­ti­mal length of the in­duc­tion coil, the step size of the scan, and the high­est order of pseudo-mul­ti­poles in the field re­con­struc­tion. This paper pre­sents the the­ory of the mea­sure­ment method, the data ac­qui­si­tion and de­con­vo­lu­tion, and the de­sign and pro­duc­tion of a sad­dle-shaped, ro­tat­ing-coil mag­ne­tome­ter.  
slides icon Slides SUPAG03 [4.548 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SUPAG03  
About • paper received ※ 18 October 2018       paper accepted ※ 27 January 2019       issue date ※ 26 January 2019  
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TUPAF08 A Full Field-Map Modeling of Cornell-BNL CBETA 4-Pass Energy Recovery Linac FFAG, linac, optics, simulation 186
 
  • F. Méot, S.J. Brooks, D. Trbojevic, N. Tsoupas
    BNL, Upton, Long Island, New York, USA
  • J.A. Crittenden
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy
The Cor­nell-BNL Elec­tron Test Ac­cel­er­a­tor (CBETA) is a four-pass, 150 MeV en­ergy re­cov­ery linac (ERL), now in con­struc­tion at Cor­nell. A sin­gle fixed-field al­ter­nat­ing gra­di­ent (FFAG) beam line re­cir­cu­lates the four en­er­gies, 42, 78, 114 and 150 MeV. The re­turn loop is com­prised of 107 quadru­pole-dou­blet cells, built using Hal­bach per­ma­nent mag­net tech­nol­ogy. Spreader and com­biner sec­tions (4 in­de­pen­dent beam lines each) con­nect the 36 MeV linac to the FFAG loop. We pre­sent here a start-to-end sim­u­la­tion of the 4-pass ERL, en­tirely, and ex­clu­sively, based on the use of mag­netic field maps to model the mag­nets and cor­rec­tors. There are para­mount rea­sons for that and this is dis­cussed, de­tailed out­comes are pre­sented, to­gether with com­par­isons with reg­u­lar beam trans­port (map­ping based) tech­niques. 		 
slides icon Slides TUPAF08 [2.568 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF08  
About • paper received ※ 23 October 2018       paper accepted ※ 07 December 2018       issue date ※ 26 January 2019  
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TUPAG14 Constrained Multi-Objective Shape Optimization of Superconducting RF Cavities to Counteract Dangerous Higher Order Modes cavity, HOM, impedance, superconducting-RF 293
 
  • M. Kranjcevic, P. Arbenz
    ETH, Zurich, Switzerland
  • A. Adelmann
    PSI, Villigen PSI, Switzerland
  • S. Gorgi Zadeh, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  
  High cur­rent stor­age rings, such as the Z op­er­at­ing mode of the FCC-ee, re­quire su­per­con­duct­ing radio fre­quency (RF) cav­i­ties that are op­ti­mized with re­spect to both the fun­da­men­tal mode and the dan­ger­ous higher order modes. In order to op­ti­mize the shape of the RF cav­ity, a con­strained multi-ob­jec­tive op­ti­miza­tion prob­lem is solved using a mas­sively par­al­lel im­ple­men­ta­tion of an evo­lu­tion­ary al­go­rithm. Ad­di­tion­ally, a fre­quency-fix­ing scheme is em­ployed to deal with the con­straint on the fre­quency of the fun­da­men­tal mode. Fi­nally, the com­puted Pareto front ap­prox­i­ma­tion and an RF cav­ity shape with de­sired prop­er­ties are shown.  
slides icon Slides TUPAG14 [3.001 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG14  
About • paper received ※ 19 October 2018       paper accepted ※ 10 December 2018       issue date ※ 26 January 2019  
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WEPAF01 A Compact Permanent Magnet Spectrometer for CILEX electron, laser, permanent-magnet, simulation 320
 
  • M. Khojoyan, A. Cauchois, J. Prudent, A. Specka
    LLR, Palaiseau, France
  
  Laser Wake­field ac­cel­er­a­tion ex­per­i­ments make ex­ten- sive use of small per­ma­nent mag­nets or mag­net as­sem­blies for an­a­lyz­ing and fo­cus­ing elec­tron beams pro­duced in plasma ac­cel­er­a­tors. Be­sides being com­pact, these mag­nets have to have a large an­gu­lar ac­cep­tance for the di­ver­gent laser and elec­tron beams which im­poses con­straint of the gap size. We will pre­sent the op­ti­mized de­sign and charac- ter­i­za­tion of a 100 mm long, 2.1 Tesla per­ma­nent mag­net di­pole. Fur­ther­more, we will pre­sent the per­for­mance of such a mag­net as a spec­trom­e­ter in the CILEX/APOL­LON 10PW laser fa­cil­ity in France.  
slides icon Slides WEPAF01 [6.898 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-WEPAF01  
About • paper received ※ 15 October 2018       paper accepted ※ 28 January 2019       issue date ※ 26 January 2019  
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WEPLG03 Theoretical and Computational Modeling of a Plasma Wakefield BBU Instability plasma, wakefield, impedance, simulation 341
 
  • S.D. Webb, D.L. Bruhwiler, N.M. Cook
    RadiaSoft LLC, Boulder, Colorado, USA
  • A.V. Burov, V.A. Lebedev, S. Nagaitsev
    Fermilab, Batavia, Illinois, USA
  
  Funding: This work was supported in part by the Department of Energy, Office of Science, Office of High Energy Physics, under contract number DE-SC0018718.
Plasma wake­field ac­cel­er­a­tors achieve ac­cel­er­at­ing gra­di­ents on the order of the wave-break­ing limit, m c2 kp/e, so that higher ac­cel­er­at­ing gra­di­ents cor­re­spond to shorter plasma wave­lengths. Small-scale ac­cel­er­at­ing struc­tures, such as plasma and di­elec­tric wake­fields, are sus­cep­ti­ble to the beam break-up in­sta­bil­ity (BBU), which can be un­der­stood from the Panof­sky-Wen­zel the­o­rem: if the fun­da­men­tal ac­cel­er­at­ing mode scales as b-1 for a struc­ture ra­dius b, then the di­pole mode must scale as b-3, mean­ing that high ac­cel­er­at­ing gra­di­ents nec­es­sar­ily come with strong di­pole wake fields. Be­cause of this re­la­tion­ship, any plasma-ac­cel­er­a­tor-based fu­ture col­lider will re­quire de­tailed study of the trade-offs be­tween ex­tract­ing the max­i­mum en­ergy from the dri­ver and mit­i­gat­ing the beam break-up in­sta­bil­ity. Re­cent the­o­ret­i­cal work* pre­dicts the trade­off be­tween the wit­ness bunch sta­bil­ity and the amount of en­ergy that can be ex­tracted from the drive bunch, a so-called ef­fi­ciency-in­sta­bil­ity re­la­tion . We will dis­cuss the beam break-up in­sta­bil­ity and the ef­fi­ciency-in­sta­bil­ity re­la­tion and the the­o­ret­i­cal as­sump­tions made in reach­ing this con­clu­sion. We will also pre­sent pre­lim­i­nary par­ti­cle-in-cell sim­u­la­tions of a beam-dri­ven plasma wake­field ac­cel­er­a­tor used to test the do­main of va­lid­ity for the as­sump­tions made in this model.
* V. Lebedev, A. Burov, and S. Nagaitsev, "Efficiency versus
instability in plasma accelerators", Phys. Rev. Acc. Beams 20, 121301
(2017). 		 
slides icon Slides WEPLG03 [2.234 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-WEPLG03  
About • paper received ※ 01 November 2018       paper accepted ※ 28 January 2019       issue date ※ 26 January 2019  
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