Keyword: HOM
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SAPAG04 HOM-Mitigation for Future SPS 33-Cell 200 MHz Accelerating Structures damping, impedance, cavity, coupling 35
 
  • P. Kramer, C. Vollinger
    CERN, Geneva, Switzerland
  
  The CERN SPS 200 MHz trav­el­ling wave (TW) ac­cel­er­at­ing struc­tures pose an in­ten­sity lim­i­ta­tion for the planned High Lu­mi­nos­ity (HL-) LHC up­grade. Higher-or­der modes (HOMs) around 630 MHz have been iden­ti­fied as one of the main sources of lon­gi­tu­di­nal multi-bunch in­sta­bil­i­ties. Im­proved mit­i­ga­tion of these HOMs with re­spect to today’s HOM-damp­ing scheme is there­fore an es­sen­tial part of the LHC in­jec­tors up­grade (LIU) pro­ject. The basic prin­ci­ples of HOM-cou­plers in cav­i­ties and today’s damp­ing scheme are re­viewed, be­fore il­lus­trat­ing the nu­mer­ous re­quire­ments an im­proved damp­ing scheme for the fu­ture 33-cell struc­tures must ful­fil. These are, amongst oth­ers, the mit­i­ga­tion of HOMs sit­u­ated in the lower part of the struc­ture where there are no ac­cess ports for ex­trac­tion, a suf­fi­cient over­all damp­ing per­for­mance and an ac­cept­able in­flu­ence on the fun­da­men­tal ac­cel­er­at­ing pass­band (FPB). Dif­fer­ent ap­proaches tack­ling these chal­lenges are in­ves­ti­gated and their per­for­mance, ad­van­tages and pit­falls are eval­u­ated by ACE3P and CST elec­tro­mag­netic (EM) field solver suites.  
slides icon Slides SAPAG04 [2.184 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SAPAG04  
About • paper received ※ 19 October 2018       paper accepted ※ 24 October 2018       issue date ※ 26 January 2019  
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TUPAF02 SixTrack Project: Status, Runtime Environment, and New Developments simulation, scattering, collimation, optics 172
 
  • R. De Maria, J. Andersson, L. Field, M. Giovannozzi, P.D. Hermes, N. Hoimyr, G. Iadarola, S. Kostoglou, E.H. Maclean, E. McIntosh, A. Mereghetti, J. Molson, V.K.B. Olsen, D. Pellegrini, T. Persson, M. Schwinzerl, K.N. Sjobak
    CERN, Geneva, Switzerland
  • E.H. Maclean
    University of Malta, Information and Communication Technology, Msida, Malta
  • S. Singh
    Indian Institute of Technology Madras, Chennai, India
  • K.N. Sjobak
    University of Oslo, Oslo, Norway
  • I. Zacharov
    EPFL, Lausanne, Switzerland
  
  Funding: Research supported by the HL-LHC project and Google Summer of Code 2018.
Six­Track is a sin­gle-par­ti­cle track­ing code for high-en­ergy cir­cu­lar ac­cel­er­a­tors rou­tinely used at CERN for the Large Hadron Col­lider (LHC), its lu­mi­nos­ity up­grade (HL-LHC), the Fu­ture Cir­cu­lar Col­lider (FCC), and the Super Pro­ton Syn­chro­tron (SPS) sim­u­la­tions. The code is based on a 6D sym­plec­tic track­ing en­gine, which is op­ti­mised for long-term track­ing sim­u­la­tions and de­liv­ers fully re­pro­ducible re­sults on sev­eral plat­forms. It also in­cludes mul­ti­ple scat­ter­ing en­gines for beam-mat­ter in­ter­ac­tion stud­ies, as well as fa­cil­i­ties to run in­te­grated sim­u­la­tions with FLUKA and GEANT4. These fea­tures dif­fer­en­ti­ate Six­Track from gen­eral-pur­pose, op­tics-de­sign soft­ware like MAD-X. The code re­cently un­der­went a major re­struc­tur­ing to merge ad­vanced fea­tures into a sin­gle branch, such as mul­ti­ple ion species, in­ter­face with ex­ter­nal codes, and high-per­for­mance input/out­put (XRootD, HDF5). This re­struc­tur­ing also re­moved a large num­ber of build flags, in­stead en­abling/dis­abling the func­tion­al­ity at run-time. In the process, the code was moved from For­tran 77 to For­tran 2018 stan­dard, also al­low­ing and achiev­ing a bet­ter mod­u­lar­iza­tion. Physics mod­els (beam-beam ef­fects, RF-mul­ti­poles, cur­rent car­ry­ing wires, so­le­noid, and elec­tron lenses) and meth­ods (sym­plec­tic­ity check) have also been re­viewed and re­fined to offer more ac­cu­rate re­sults. The SixDesk run­time en­vi­ron­ment al­lows the user to man­age the large batches of sim­u­la­tions re­quired for ac­cu­rate pre­dic­tions of the dy­namic aper­ture. SixDesk sup­ports CERN LSF and HT­Con­dor batch sys­tems, as well as the BOINC in­fra­struc­ture in the frame­work of the LHC@​Home vol­un­teer­ing com­put­ing pro­ject. Six­Track­Lib is a new li­brary aimed at pro­vid­ing a portable and flex­i­ble track­ing en­gine for sin­gle- and multi-par­ti­cle prob­lems using the mod­els and for­mal­ism of Six­Track. The track­ing rou­tines are im­ple­mented in a pa­ram­e­trized C code that is spe­cialised to run vec­tor­ized in CPUs and GPUs, by using SIMD in­trin­sics, OpenCL 1.2, and CUDA tech 		 
slides icon Slides TUPAF02 [0.938 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF02  
About • paper received ※ 18 October 2018       paper accepted ※ 24 October 2018       issue date ※ 26 January 2019  
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TUPAF14 Analytical Calculations for Thomson Backscattering Based Light Sources electron, laser, radiation, scattering 215
 
  • P.I. Volz, A. Meseck
    HZB, Berlin, Germany
  
  There is a ris­ing in­ter­est in Thom­son-backscat­ter­ing based light sources, as scat­ter­ing in­tense laser ra­di­a­tion on MeV elec­trons pro­duces high en­ergy pho­tons that would re­quire GeV or even TeV elec­tron beams when using con­ven­tional un­du­la­tors or dipoles. Par­tic­u­larly, medium en­ergy high bright­ness beams de­liv­ered by LINACs or En­ergy Re­cov­ery LINACs, such as BERLinPro being built at Helmholtz-Zen­trum Berlin, seem suit­able for these sources. In order to study the merit of Thom­son-backscat­ter­ing-based light sources, we are de­vel­op­ing an an­a­lyt­i­cal code to sim­u­late the char­ac­ter­is­tics of the Thom­son scat­tered ra­di­a­tion. The code cal­cu­lates the dis­tri­b­u­tion of scat­tered ra­di­a­tion de­pend­ing on the in­ci­dent angle and po­lar­iza­tion of the laser ra­di­a­tion. Also the im­pact of the in­ci­dent laser pro­file and the full 6D bunch pro­file, in­clud­ing mi­crobunch­ing, are in­cor­po­rated. The Sta­tus of the code and first re­sults will be pre­sented.  
slides icon Slides TUPAF14 [3.289 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF14  
About • paper received ※ 21 October 2018       paper accepted ※ 28 January 2019       issue date ※ 26 January 2019  
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TUPAG04 Statistical Analysis of the Eigenmode Spectrum in the SRF Cavities with Mechanical Imperfections cavity, SRF, linac, cryomodule 265
 
  • A. Lunin, T.N. Khabiboulline, N. Solyak, A.I. Sukhanov, V.P. Yakovlev
    Fermilab, Batavia, Illinois, USA
  
  Funding: Work is supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy
The su­per­con­duct­ing radio fre­quency (SRF) tech­nol­ogy is pro­gress­ing rapidly over last decades to­ward high ac­cel­er­at­ing gra­di­ents and low sur­face re­sis­tance mak­ing fea­si­ble the par­ti­cle ac­cel­er­a­tors op­er­a­tion with high beam cur­rents and long duty fac­tors. How­ever, the co­her­ent RF losses due to high order modes (HOMs) ex­ci­ta­tion be­comes a lim­it­ing fac­tor for these regimes. In spite of the op­er­at­ing mode, which is tuned sep­a­rately, the pa­ra­me­ters of HOMs vary from one cav­ity to an­other due to fi­nite me­chan­i­cal tol­er­ances dur­ing cav­i­ties fab­ri­ca­tion. It is vital to know in ad­vance the spread of HOM pa­ra­me­ters in order to pre­dict un­ex­pected cryo­genic losses, over­heat­ing of beam line com­po­nents and to keep sta­ble beam dy­nam­ics. In this paper we pre­sent the method of gen­er­at­ing the unique cav­ity geom­e­try with im­per­fec­tions while pre­serv­ing op­er­at­ing mode fre­quency and field flat­ness. Based on the eigen­mode spec­trum cal­cu­la­tion of se­ries of ran­domly gen­er­ated cav­i­ties we can ac­cu­mu­late the data for the eval­u­a­tion the HOM sta­tis­tics. Fi­nally, we de­scribe the pro­ce­dure for the es­ti­ma­tion of the prob­a­bil­ity of the res­o­nant HOM losses in the SRF res­onators. The study of these ef­fects leads to spec­i­fi­ca­tions of SC cav­ity and cry­omod­ule and can sig­nif­i­cantly im­pact on the ef­fi­ciency and re­li­a­bil­ity of the ma­chine op­er­a­tion 		 
slides icon Slides TUPAG04 [1.810 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG04  
About • paper received ※ 15 October 2018       paper accepted ※ 28 January 2019       issue date ※ 26 January 2019  
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TUPAG07 Efficient Computation of Lossy Higher Order Modes in Complex SRF Cavities Using Reduced Order Models and Nonlinear Eigenvalue Problem Algorithms cavity, GUI, SRF, impedance 270
 
  • H.W. Pommerenke, J. Heller, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  
  Su­per­con­duct­ing radio fre­quency (SRF) cav­i­ties meet the de­mand­ing per­for­mance re­quire­ments of mod­ern ac­cel­er­a­tors and high-bril­liance light sources. For the op­er­a­tion and de­sign of such res­onators, a very pre­cise knowl­edge of their elec­tro­mag­netic res­o­nances is re­quired. The non-triv­ial cav­ity shape de­mands a nu­mer­i­cal so­lu­tion of Maxwell’s equa­tions to com­pute the res­o­nant eigen­fre­quen­cies, eigen­modes, and their losses. For large and com­plex struc­tures this is hardly pos­si­ble on con­ven­tional hard­ware due to the high num­ber of de­grees of free­dom re­quired to ob­tain an ac­cu­rate so­lu­tion. In pre­vi­ous work it has been shown that the con­sid­ered prob­lems can be solved on work­sta­tion com­put­ers with­out ex­ten­sive sim­pli­fi­ca­tion of the struc­ture it­self by a com­bi­na­tion of State-Space Con­cate­na­tion (SSC) and New­ton it­er­a­tion to solve the aris­ing non­lin­ear eigen­value prob­lem (NLEVP). First, SSC is ap­plied to the com­plex, closed and thus loss­less RF struc­ture. SSC em­ploys a com­bi­na­tion of model order re­duc­tion and do­main de­com­po­si­tion, greatly re­duc­ing the com­pu­ta­tional ef­fort by ef­fec­tively lim­it­ing the con­sid­ered fre­quency do­main. Next, a per­tur­ba­tion ap­proach based on SSC is used to de­scribe the res­o­nances of the same geom­e­try sub­ject to ex­ter­nal losses. This re­sults in a NLEVP which can be solved ef­fi­ciently by New­ton’s method. In this paper, we ex­pand the NLEVP so­lu­tion al­go­rithm by a con­tour in­te­gral tech­nique, which in­creases the com­plete­ness of the so­lu­tion set.  
slides icon Slides TUPAG07 [11.204 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG07  
About • paper received ※ 18 October 2018       paper accepted ※ 24 October 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, dipole, 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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