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Genesis /ALICE Benchmarking

Genesis /ALICE Benchmarking. Igor Zagorodnov Beam Dynamics Group Meeting 17.03.08. Genesis 1.3 (S.Reiche et al). ALICE. 1D/2D/3D 3D azimuthal field solver (Neumann) Leap-Frog integrator Perfectly Matched Layer transverse motion simplified model parallel (MPI)

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Genesis /ALICE Benchmarking

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  1. Genesis /ALICE Benchmarking Igor Zagorodnov Beam Dynamics Group Meeting 17.03.08

  2. Genesis 1.3 (S.Reiche et al) ALICE • 1D/2D/3D • 3D azimuthal field solver (Neumann) • Leap-Frog integrator • Perfectly Matched Layer • transverse motion • simplified model • parallel (MPI) • tested by me on the examples from the book of SSY • only 3D • 3D Cartesian field solver (ADI) • Runge-Kutta integrator • Dirichlet boundary conditions • transverse motion • many other physics • parallel (MPI) (~Saldin et al, 2000 „The Physics …“,)

  3. 2.5 MeV

  4. Genesis vs. ALICE / Energy Spread (round Gaussian beam, Gaussian energy spread, parallel motion only) SASE 2 parameters ALICE Genesis W = 4 kW

  5. How to simulate emmitance with laminar particle motion only? • E. Saldin et al, TESLA-FEL 95-02 (1995); • S.Reiche PhD Thesis (1999). - E. Saldin et al, The Physics of Free Electron Lasers (2000) - E. Saldin et al, DESY 05-164 (2005)

  6. Genesis vs. ALICE / Emmitance (round Gaussian beam, Gaussian energy spread) ALICE (laminar) Genesis

  7. Genesis vs. ALICE (emittance parameter fit) Field growth rate Genesis ALICE (laminar)

  8. Genesis vs. ALICE with laminar motion ALICE (laminar) Genesis Detuning corresponds to maximal growth rate in linear regime The transverse motion has to be implemented in ALICE

  9. I=5KA Nl ~10 400 Genesis vs. ALICE with transverse motion P0 = 4 kW Genesis (N=6e4) 19% Genesis (N=3e4) Alice (N=6e4) Alice (N=3e4) The difference in saturation length is 7 %. The difference in power gain is 19 %. The difference does not reduce with changing of the discrete model parameters ?!.

  10. GINGER/GENESIS results for “0-order” 200-pC case • Observations: • Again, GENESIS shows slightly longer gain length, 10-m later saturation but 15% higher power • Again, GINGER shows deeper post-saturation power oscillation • Little sensitivity (2 m, 7%) in GINGER results to 8X particle number increase • Possible reasons for differences: • bugs • slight differences in initial e-beam properties (e.g. mismatch) • grid effects (e.g. outer boundary) • ??? William M. Fawley, ICFA 2003 Workshop on Start-to-End Numerical Simulations of X-RAY FEL’s

  11. About advantages of the „quiet start“ see, for example, in Bridsall C.K., Langdon A.B., Plasma Physics via Computer Simulations, 1991 Dawson J.M, Particle simulation of Plasmas // Reviews of Modern Physics, 1983

  12. Properties of the Normal macroparticle distribution

  13. Properties of the Normal macroparticle distribution

  14. Quiet start ? ASTRA Genesis ALICE clustering What is the reason?

  15. Quiet start ? Normal Uniform The polar form of Box-Muller algorithm (in Genesis) maps the „quiet“ uniform distribution in a clustered normal distribution.

  16. Quiet start ? ALICE Genesis clustering

  17. Quiet start ? ALICE Genesis clustering

  18. ASTRA

  19. Modified Genesis vs. ALICE with transverse motion P0 = 4000 Watt Genesis (modified) (N=6e4) Alice (N=6e4)

  20. The transformation used in ALICE It uses the straightforward transformation by inverse error function It transforms the uniform distribution Xi (0,1)to the normal distribution Yi (m, s). This transformation does not destroy the „quiet start“.

  21. Convergence at saturation Genesis Genesis (modified) Genesis Genesis (modified) ALICE ALICE Genesis: Hammersley and Box-Mueller Genesis (modified): Hammersley and the inverse error function ALICE: Sobol and the inverse error function I=5KA Nl ~10 400

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