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  1. Recent developments of RESTRAXOptimization of neutron optics and virtual triple-axis experimentsJan Šaroun1, Jiří Kulda2, Vasyl Ryukhtin11Nuclear Physics Institute, Řež2Institute Laue-Langevin, Grenoble • Contents: • Overview of new capabilities of the RESTRAX software • Numerical optimizations of TAS parameters • Virtual TAS experiments - simulations with selected sample kernels RESTRAX homepage::http://omega.ujf.cas.cz/restrax/ NMI3 meeting, ISIS, September 26-29, 2005

  2. SIMRES Version for instrument optimizations - more detailed simulation of TAS components - mapping neutron beam in phase-space - tools for numerical optimization

  3. SIMRES - virtual triple axis spectrometer source collimator segments sample crystals detector + setups that can be mapped onto a classical TAS layout (powder and strain diffratometers) multi-purpose components: source:arbitrary energy, spatial and angular distributions via look-up tables crystals:focusing arrays of elastically bent or mosaic crystals (incl. simulated extinction effects, absorption, etc...) collimators:universal components describing: Sollers, curved guides or benders, elliptic or parabolic guides, lobster-eye devices multiplexing:flat-cone multianalyzer and multidetector systems NMI3 meeting, ISIS, September 26-29, 2005

  4. Ray-tracing & numerical optimizations figure of merit, fm(a1, a2, ...): I ... incident intensity DE ... energy spread I / DE, I / DE2 ... inelastic scattering I / Dq, I /Dq2 ... diffraction free parameters, a1, a2, ... an crystal curvature, mosaicity, cutting angle, guide dimensions, curvature, divergence, ... Fixed setup  fast ray-tracing code, 103 -104 counts/sec ray-tracing results are used to find extremum of fm numerically. Speed problem: number of simulations / iteration = 1+2n2 n  4 acceptable (CPU time < 1 hour) NMI3 meeting, ISIS, September 26-29, 2005

  5. Lobster-eye device & focusing monochromator monochromatic beam + spatial focusing monochromatic focusing spatial focusing ? • Simultaneous optimization of the crystal curvatures and guide parameters • mutual correlations • ray-tracing: realistic model of the instrument components NMI3 meeting, ISIS, September 26-29, 2005

  6. Lobster-eye device & focusing monochromator • Lobster-eye device • 20 (hor.) or 30 (ver.) blades • thickness 0.5 mm • m=3 supermirror (concave sides) • elliptic & parabolic profiles • optimization: entry & exit width • TAS - IN14 setup • cold source • straight 58Ni guide, 6x12 cm2 • monochromator: PG 002, doubly focusing, l=4.05 Å • target (sample) area: 3x3 mm2 • optimization: crystal curvatures NMI3 meeting, ISIS, September 26-29, 2005

  7. Focusing on small samples Parabolic guide + perfect focusing of a parallel beam - large reflection angle at the entry NMI3 meeting, ISIS, September 26-29, 2005

  8. Focusing on small samples Elliptic guide - parallel beam does not focus to a point + lamellae are parallel at the entry NMI3 meeting, ISIS, September 26-29, 2005

  9. Lobster-eye device & focusing monochromator Optimization in 2 dimensions x Mapping the parameter space adjustable parameters: horizontal: 1) monochromator: 1/RH 2) guide: exit width vertical: 1) monochromator: 1/RV 2) guide: exit height Number of blades is fixed  adjusting focal distance Resolution 32x32 pixels 1024 simulations NMI3 meeting, ISIS, September 26-29, 2005

  10. Mapping of parameter space Optimization route in 2 dimensions Elliptic blades Intensity/DE Intensity horizontal vertical NMI3 meeting, ISIS, September 26-29, 2005

  11. Mapping of parameter space Optimization route in 2 dimensions Parabolic blades Intensity/DE Intensity horizontal vertical NMI3 meeting, ISIS, September 26-29, 2005

  12. Lobster-eye device & focusing monochromator Optimization in 3 dimensions adjustable parameters: horizontal: 1) monochromator: 1/RH 2) guide: entry width 3) guide: exit width vertical: 1) monochromator: 1/RV 2) guide: entry height 3) guide: exit height Number of blades is fixed  adjusting focal distance and spacing between blades mapping in 3D is not feasible  32768 simulations/map … NMI3 meeting, ISIS, September 26-29, 2005

  13. Lobster-eye device & focusing monochromator Optimization in 3 dimensions Elliptic blades NMI3 meeting, ISIS, September 26-29, 2005

  14. Lobster-eye device & focusing monochromator Optimization in 3 dimensions Parabolic blades NMI3 meeting, ISIS, September 26-29, 2005

  15. Lobster-eye device & focusing monochromator Optimization in 3 dimensions Focusing monochromator only NMI3 meeting, ISIS, September 26-29, 2005

  16. Lobster-eye device & focusing monochromator Total intensity (whole beam) [109/s]: parabolic 1.3 elliptic 1.6 no 3.4 Optimization in 3 dimensions Results NMI3 meeting, ISIS, September 26-29, 2005

  17. RESTRAX Version for TAS resolution simulations and data analysis - simplified TAS setup with faster ray-tracing code - 4D resolution functions + convolution with S(Q,w) - dynamically loaded modules with S(Q,w) model - non-linear data fitting

  18. Sample “exchanger” in RESTRAX TAS ray-tracing, R(Q,w) • dynamically loaded modules, S(Q,w) • Damped harmonic oscillators • Damped harmonic oscillators, free dispersion gradient • Bond charge model (phonons in Si, Ge, ...) • Incommensurate fluctuations (diffuse satellites) • … others defined by users 4D convolution • data simulation • data fitting NMI3 meeting, ISIS, September 26-29, 2005

  19. TAS: conventional arrangement monochromator analyzer sample detector NMI3 meeting, ISIS, September 26-29, 2005

  20. TAS: flat-cone analyzer detector monochromator analyzer sample NMI3 meeting, ISIS, September 26-29, 2005

  21. TAS: flat-cone multianalyzer detector monochromator analyzer sample NMI3 meeting, ISIS, September 26-29, 2005

  22. Sweeping reciprocal space a4 a3 non-linear scans in rec. lattice New flat-cone analyzer for ILL TAS instruments, 32 channels IN20: monochromator Si, ki=3 A-1 NMI3 meeting, ISIS, September 26-29, 2005

  23. Example 1: Incommensurate sattelites E 010 210 M.C. ray-tracing & convolution with S(Q,E) 000 200 010 210 110 raw data Incommensurate sattelites: DE  NMI3 meeting, ISIS, September 26-29, 2005

  24. Example 1: Incommensurate satellites ... and transformed to rec. lattice space NMI3 meeting, ISIS, September 26-29, 2005

  25. Example 1: Incommensurate satellites detail ... NMI3 meeting, ISIS, September 26-29, 2005

  26. Example 2: bond charge model(BCM) Model describing phonons in diamond lattice (Si, Ge, a-Sn, ...) Eigenvalues & eigenvectors are calculated using coulombic potential of bond charges for each of Q,E points representing simulated TAS resolution function W. Weber, Phys. Rev. B 15 (1977) 4789. phonons in Si NMI3 meeting, ISIS, September 26-29, 2005

  27. Phonons in Si E=10 meV E=20 meV NMI3 meeting, ISIS, September 26-29, 2005

  28. Phonons in Si E=30 meV E=40 meV NMI3 meeting, ISIS, September 26-29, 2005

  29. Phonons in Si E=50 meV E=60 meV NMI3 meeting, ISIS, September 26-29, 2005

  30. Phonons in Si convolution with flat-cone resolution simulated by ray-tracing CPU time: 4 hours MC simulation for IN20 kf=3A-1, E=20meV 64 channels, Da4=1.25o 91 steps, Da3=0.75o E=20 meV NMI3 meeting, ISIS, September 26-29, 2005

  31. Summary • Numerical optimizations • using ray-tracing simulations in numerical optimization is feasible • multiple correlated TAS parameters can be optimized with respect to different figures of merit • Lobster-eye guides • high flux at small samples, leaves space for sample environment • vertical and horizontal focusing can be splitted in 2 guide sections • alternative to focusing monochromators at quasiparallel beams • Dynamically loaded S(Q,w) modules • data simulations and fitting with various sample kernels • extensions provided by users RESTRAX homepage::http://omega.ujf.cas.cz/restrax/ NMI3 meeting, ISIS, September 26-29, 2005