Author: van Rienen, U.
Paper Title Page
TUPAG01 Computation of Eigenmodes in the BESSY VSR Cavity Chain by Means of Concatenation Strategies 253
 
  • T. Flisgen, A.V. Vélez
    HZB, Berlin, Germany
  • J. Heller, G. Zadeh, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
 
  Funding: The research leading to these results was supported by the German Bundesministerium für Bildungund Forschung, Land Berlin and grants of Helmholtz Association
In­vited Talk: The com­pu­ta­tion of eigen­modes in chains of su­per­con­duct­ing cav­i­ties with asym­met­ric cou­plers is a de­mand­ing prob­lem. This prob­lem typ­i­cally re­quires the use of high-per­for­mance com­put­ers in com­bi­na­tion with ded­i­cated soft­ware pack­ages. Al­ter­na­tively, the eigen­modes of chains of su­per­con­duct­ing cav­i­ties can be de­ter­mined by the so-called State-Space Con­cate­na­tion (SSC) ap­proach that has been de­vel­oped at the Uni­ver­sity of Ro­s­tock. SSC is based on the de­com­po­si­tion of the full chain into in­di­vid­ual seg­ments. Sub­se­quently, the RF prop­er­ties of every seg­ment are de­scribed by re­duced-or­der mod­els. These re­duced-or­der mod­els are con­cate­nated to a re­duced-or­der model of the en­tire chain by means of al­ge­braic side con­straints aris­ing from con­ti­nu­ity con­di­tions of the fields across the de­com­po­si­tion planes. The con­structed re­duced-or­der model de­scribes the RF prop­er­ties of the com­plete struc­ture so that the field dis­tri­b­u­tions, the cou­pling im­ped­ances and the ex­ter­nal qual­ity fac­tors of the eigen­modes of the full cav­ity chain are avail­able. In con­trast to di­rect meth­ods, SSC al­lows for the com­pu­ta­tion of the eigen­modes of cav­ity chains using desk­top com­put­ers. The cur­rent con­tri­bu­tion re­vises the scheme using the BESSY VSR cav­ity chain as an ex­am­ple. In ad­di­tion, a com­par­i­son be­tween a di­rect com­pu­ta­tion of a spe­cific lo­cal­ized mode is de­scribed.
 
slides icon Slides TUPAG01 [3.483 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG01  
About • paper received ※ 21 October 2018       paper accepted ※ 28 January 2019       issue date ※ 26 January 2019  
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TUPAG02 First Steps Towards a New Finite Element Solver for MOEVE PIC Tracking 260
 
  • U. van Rienen, C.R. Bahls, J. Heller, D. Zheng
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • U. van Rienen
    University of Rostock, Rostock, Germany
 
  Funding: This work has been supported by the German Federal Ministry for Research and Education BMBF under contract 015K16HRA.
A rel­e­vant task in de­sign­ing high-bril­liance light sources based on high-cur­rent lin­ear ac­cel­er­a­tors (e.g. En­ergy Re­cov­ery Linacs (ERLs)) con­sists in sys­tem­atic in­ves­ti­ga­tions of ion dy­nam­ics in the vac­uum cham­ber of such ma­chines. This is of high im­por­tance since the par­a­sitic ions gen­er­ated by the elec­tron beam turned out to be a cur­rent-lim­it­ing fac­tor for many syn­chro­tron ra­di­a­tion sources. In par­tic­u­lar, the planned high cur­rent op­er­a­tion at ERL fa­cil­i­ties re­quires a pre­cise analy­sis and an ac­cu­rate de­vel­op­ment of ap­pro­pri­ate mea­sures for the sup­pres­sion of ion-in­duced beam in­sta­bil­i­ties. The lon­gi­tu­di­nal trans­port of ions through the whole ac­cel­er­a­tor plays a key role for the es­tab­lish­ment of the ion con­cen­tra­tion in the ma­chine. Using the Par­ti­cle-in-Cell (PIC) method, we started re­design­ing our code MOEVE PIC Track­ing in order to allow for the fast es­ti­ma­tion of the ef­fects of ions on the beam dy­nam­ics. For that, we ex­changed the pre­vi­ously used Fi­nite Dif­fer­ence (FD) method for the so­lu­tion of Pois­son’s equa­tion within the PIC solver by a solver based on the Fi­nite El­e­ment Method (FEM). Em­ploy­ing higher order FEM, we ex­pect to gain im­proved con­ver­gence rates and thus lower com­pu­ta­tional times. We chose the Open Source Frame­work FEn­iCS for our new im­ple­men­ta­tion.
 
slides icon Slides TUPAG02 [0.924 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG02  
About • paper received ※ 21 October 2018       paper accepted ※ 24 October 2018       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 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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TUPAG08
Uncertainty Quantification for the Fundamental Mode Spectrum of the European XFEL Cavities  
 
  • N. G. Georg, J. Corno, H. De Gersem, U. Römer, S. Schöps
    TEMF, TU Darmstadt, Darmstadt, Germany
  • S. Gorgi Zadeh, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • A.A. Sulimov
    DESY, Hamburg, Germany
 
  Funding: The authors would like to acknowledge the support by the DFG (German Research Foundation) in the framework of the Scientific Network SCHM 3127/1,2 that provided the basis for this collaborative work.
The fun­da­men­tal mode spec­trum of su­per­con­duct­ing cav­i­ties is sen­si­tive to small geom­e­try de­for­ma­tions in­tro­duced by the man­u­fac­tur­ing process. In this work we con­sider vari­a­tions in the equa­to­r­ial and iris radii of the 1.3 GHz TESLA cav­i­ties used at the Eu­ro­pean XFEL. The cav­i­ties with slightly per­turbed geom­e­try are sim­u­lated using a fi­nite el­e­ment based eigen­value solver. Em­ploy­ing un­cer­tainty quan­tifi­ca­tion meth­ods such as sparse-grids, sta­tis­ti­cal in­for­ma­tion about the fun­da­men­tal mode spec­trum can be ef­fi­ciently cal­cu­lated. More­over, using global sen­si­tiv­ity analy­sis, in par­tic­u­lar Sobol in­dices, the im­pact of the in­di­vid­ual geom­e­try pa­ra­me­ters on the quan­ti­ties of in­ter­est, i.e. res­o­nance fre­quen­cies, field-flat­ness and the cell-to-cell cou­pling co­ef­fi­cient, can be com­puted. We will ex­plain im­por­tant as­pects of the un­cer­tainty quan­tifi­ca­tion method­ol­ogy and give nu­mer­i­cal re­sults for il­lus­tra­tion.
 
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TUPAG14 Constrained Multi-Objective Shape Optimization of Superconducting RF Cavities to Counteract Dangerous Higher Order Modes 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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