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Electromagnetic field simulations for accelerator optimization

Electromagnetic field simulations for accelerator optimization . Alexej Grudiev CERN, BE-RF 1 st oPAC Workshop: Grand Challenges in Accelerator Optimization, 26-27 June 2013, CERN. Outline. A review of tools for electromagnetic field simulations used at CERN will be given.

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Electromagnetic field simulations for accelerator optimization

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  1. Electromagnetic field simulations for accelerator optimization Alexej Grudiev CERN, BE-RF 1stoPAC Workshop: Grand Challenges in Accelerator Optimization, 26-27 June 2013, CERN

  2. Outline • A review of tools for electromagnetic field simulations used at CERN will be given. • A number of examples of its usage will be presented covering several areas of accelerator component design and optimization both RF and non-RF equipment: • accelerating cavities, • collimation devices, • etc. • A brief review of CLIC main linac RF frequency and accelerating gradient optimization will be given as an example of incorporating electromagnetic field simulation into a global optimization process including both • constraints coming from the beam dynamics simulations and • the empirical RF constraints related to the high gradient linac operation.

  3. Packages for computer simulations of electromagnetic EM fields and more

  4. CST Studio Suite CST STUDIO SUITE: - CST MWS - CST DS - CST EMS - CST PS - CST MPS - CST PCBS - CST CS - CST MICROSTRIPES - Antenna Magus

  5. CST: All you need in one package • Powerful and user-friendly Input: • Probably the best time domain (TD) solver for wakefields or beam coupling impedance calculations (MAFIA) • Beta < 1 • Finite Conductivity walls • Once geometry input is done it can be used both for TD and FD simulations • Moreover using Design Studio (DS) it can be combined with the other studios for multiphysicsand integrated electronics simulation, but this is relatively fresh fields of expertise for CST • Accelerator physics oriented post processor, especially in MWS and PS • Enormous progress over the last few years compared to the competitors. Courtesy of Igor Syratchev An example of what can be solved easily on a standard PC

  6. CST (examples) Two examples of what can be solved on bigger PC: 128 GB of RAM and 24 CPUs CLIC accelerating structure from Cu with HOM damping loads from SiC (frequency dependent lossy material) Giovanni De Michele

  7. CST (examples) Wx [V/pC] Transverse wake at offset of 0.5 mm Zx [Ω] s [mm] Transverse beam couping impedance at offset of 0.5 mm f [GHz]

  8. CST (examples) LHC TDI 5m long with ferrite Benoit Salvant

  9. CST MWS: Example. S-parameters in CLIC Crab cavity Mesh view Praveen Ambattu

  10. CST: Shortcomings Cartesian mesh: Especially in FD can results to less accurate calculations of frequency, Q-factor, surface fields compared to tetrahedral mesh (HFSS, ACE3P). => if possible use tetrahedral mesh which became available recently and essentially gives the same results as FEM codes (HFSS, ACE3P). Boundary conditions can be set only in Cartesian planes No Field Calculator (HFSS) ...

  11. HFSS: Still an excellent tool for FD • High-Performance Electronic Design • Ansoft Designer • ANSYS HFSS • ANSYS Q3D Extractor • ANSYS SIwave • ANSYS TPA • Electromechanical Design • ANSYS Multiphysics • ANSYS Maxwell • ANSYS Simplorer • ANSYS PExprt • ANSYS RMxprt • Product options • AnsoftLinks for ECAD • AnsoftLinks for MCAD • ANSYS Distributed Solve • ANSYS Full-Wave SPICE • ANSYS Optimetrics • ANSYS ParICs • HFSS was and I think still is superior tool for FD simulations both S-pars and eigenmode, though CST shows significant progress in the recent years • Automatic generation and refinement of tetrahedral mesh • Most complete list of boundary conditions which can be applied on any surface • Ansoft Designer allows to co-simulate the pick-up (antenna), cables plus electronics and together with versatile Optimetrics optimise the design of the whole device • Recently HFSS became an integral part of ANSYS – reference tool for thermo-mechanical simulations -> multiphysics • REcently time-dependent solver has been released

  12. HFSS (examples, eigenmode) LHC TDI 5m long beam dump: One of the most dangerous eigenmodes at 1.227 GHz, Q = 873, Tetrahedral mesh with mixed order (0th , 1st , 2nd) elements: Ntetr = 1404891 Solution obtained on a workstation with 128 GB of RAM,

  13. HFSS (example, S-parameters) Incident plane wave excitation Port excitation O. Kononenko O. Kononenko Inverse FFT

  14. HFSS example

  15. HFSS: shortcomings • No possibility to simulate particles • Automatic mesh is not always perfect, but it has improved after adoption by ANSYS • TD and multiphysics are only recently implemented, but thermo-mechanics from ANSYS is a reference by itself • ...

  16. GdfidL: Parallel and easy to use tool • bruns@gdfidl.de • The GdfidL Electromagnetic Field simulator • GdfidL computes electromagnetic fields in 3D-structures using parallel or scalar computers. • GdfidL computes • Time dependent fields in lossfree or lossy structures. The fields may be excited by • port modes, • relativistic line charges. • Resonant fields in lossfree or lossy structures. • The postprocessor computes from these results eg. Scattering parameters, wake potentials, Q-values and shunt impedances. • Features • GdfidL computes only in the field carrying parts of the computational volume. • GdfidL uses generalised diagonal fillings to approximate the material distribution. This reduces eg. the frequency error by about a factor of ten. • For eigenvalue computations, GdfidL allows periodic boundary conditions in all three cartesian directions simultaneously. • GdfidL runs on parallel and serial computers. GdfidL also runs on clusters of workstations. • Availability • GdfidL only runs on UNIX-like operating systems.

  17. GdfidL (example) CLIC accelerating structure from Cu with HOM damping loads from SiC (frequency dependent properties)

  18. GdfidL: shortcomings • Available only under UNIX-like systems • Geometry input is limited. Often other 3D input tools have to be used. • ...

  19. ACE3P

  20. waveguide ACE3P: example CLIC two-beam module rf circuit AS AS PETS Arno Candel et. al., SLAC-PUB-14439

  21. ACE3P: shortcomings • Very complex package to use. It is not user-friendly at all and requires a lots of time to invest before it can be used efficiently • It is not a commercial product -> no manual reference, limited tech support. No it is an open source. • ...

  22. Summary for the EM simulation tools CST Larger objects in TD Better FD calculations, 3D EM + circuit co-simulation, RF + thermal + structural GdfidL ANSYS HFSS Accurate solution for very larger objects in TD and FD ACE3P

  23. CLIC main linac accelerating structure optimization. Brief Review of what was done back in 2007

  24. General layout of CLIC at 3 TeV More on CLIC : http://clic-study.org/

  25. Optimization procedure <Ea>, f, ∆φ, <a>, da, d1, d2 BD Bunch population Cell parameters N Q, R/Q, vg, Es/Ea, Hs/Ea Q1, A1, f1 Structure parameters Bunch separation BD Ns Ls, Nb η, Pin, Esmax, ∆Tmax rf constraints Cost function minimization YES NO

  26. Optimization parameter space N structures: 7 14 2 24 60 61 4 -------------- 68.866.560 All structure parameters are variable: <Eacc> = 90 – 150 MV/m, f = 10 – 30 GHz, Δφ= 120o, 150o, <a>/λ= 0.09 - 0.21, Δa/<a> = 0.01 – 0.6, d1/λ= 0.025 - 0.1, d2 > d1 Ls = 100 – 1000 mm.

  27. Structure parameter calculation From 3D simulation (few hours) to an adequate model (few seconds) Dipole mode: Ns I N Fundamental mode: P(z) η, Pin, Esmax, ∆Tmax

  28. a/λ 0.7 1.5 2.3 0.1 0.25 0.4 Cell parameter calculation Single cell parameter interpolation Q, R/Q, vg, Es/Ea, Hs/Ea d/λ WDS 2 cells

  29. Optimization constraints • Beam dynamics (BD) constraints based on the simulation of the main linac, BDS and beam-beam collision at the IP: • N – bunch population depends on <a>/λ, Δa/<a>, f and <Ea> because of short-range wakes • Ns – bunch separation depends on the long-range dipole wake and is determined by the condition: • Wt,2 · N / Ea< 10 V/pC/mm/m · 4x109 / 150 MV/m • D. Schulte • RF breakdown and pulsed surface heating (rf) constraints: • ΔTmax(Hsurfmax, tp) < 56 K • Esurfmax < 380 MV/m • Pintp1/3/Cin = 18 MW·ns1/3/mm @ X-band

  30. Optimizing Figure of Merit Luminosity per linac input power: Collision energy is constant Figure of Merit (FoM = ηLbx/N)

  31. Parametric Cost Model Total cost = Investment cost + Electricity cost for 10 years Ct = Ci+ Ce Ci= Excel{fr; Ep; tp; Ea; Ls; f; Δφ} Repetition frequency; Pulse energy; Pulse length; Accelerating gradient; Structure length (couplers included); Operating frequency; rf phase advance per cell Ce= (0.1011+7.1484/FoM)/12 [a.u.] Figure of Merit (ηL/N) in a.u. (the same as before) [a.u.]=[1e34/bx/m2•%/1e9] Hans Braun, 2006

  32. CLIC performance and cost versus gradient Ecms = 3 TeV L(1%) = 2.0 1034 cm-2s-1 Performance Cost Previous Previous New New Optimum • Performance increases with lower accelerating gradient (mainly due to higher efficiency) • Flat cost variation in 100 to 130 MV/m with a minimum around 120 MV/m

  33. CLIC performance and cost versus frequency Ecms = 3 TeV L(1%) = 2.0 1034 cm-2s-1 Performance Cost New Optimum Previous Previous New Optimum • Maximum Performance around 14 GHz • Flat cost variation in 12 to 16 GHz frequency range with a minimum around 14 GHz

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