conceptual design and performance of high throughput cold spectrometer macs n.
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Conceptual design and performance of high throughput cold spectrometer : MACS

Conceptual design and performance of high throughput cold spectrometer : MACS

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Conceptual design and performance of high throughput cold spectrometer : MACS

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  1. Conceptual design and performance of high throughput cold spectrometer : MACS Collin Broholm Johns Hopkins University and NIST Center for Neutron Research Why MACS Layout and key elements Performance Data collection Scientific program Budget and schedule Conclusion

  2. MACS development team Overall instrument design Paul Brand NIST Christoph Brocker NIST Collin Broholm JHU Jeff Lynn NIST Mike Rowe NIST Jack Rush NIST Yiming Qiu JHU Focusing Monochromator Steve Conard JHU Joe Orndorff JHU Tim Reeves JHU Gregg Scharfstein JHU Stephen Smee UMD Shielding Calculations Charles M. Eisenhauer

  3. Why cold neutrons and double focusing • To probe a range of materials must vary • keeping • To probe hard matter with low energy scales • Reduce Ei. Cold source provides the flux • Increase angular divergence before and after sample • Q and E resolved spectroscopy requires • Energy scaleJvaries more than length scalea

  4. Kinematic limits for neutron scattering Efix and 2q range determine accessible Q-E space

  5. Comparing TOF to TAS • Can focus beams with Bragg optics • Can select range of energy transfer • Can use reactor CW flux TAS like • Larger detector solid angle • E-scan with “no” moving parts • Can use pulsed spallation source peak flux TOF like

  6. NCNR Liquid Hydrogen cold source MACS Beam New cold source to be installed in 2001 will double flux

  7. Overview of MACS Design by C. Brocker, C. Wrenn, and M. Murbach

  8. Bragg focusing Focusing Monochromator Source Sample Rowland Circle

  9. Doubly Focusing Monochromator Design by Stephen Smee, G. Scharfstein et al.

  10. Blade profile chosen so blades form arc when compressed S. Smee et al. Provisional patent pending (2000)

  11. Focusing mechanics is out of beam Vertical Horizontal Design by Stephen Smee, G. Scharfstein et al.

  12. Prototype performance 2 cm JHU IDG photo, prototype, and measurement

  13. Constrained optimization : crystal mosaic Flux versus mosaic at fixed 0.2 meV energy resolution

  14. Effects of cystal misalignment

  15. Projected performance analytical approximation C. Broholm, Nucl. Instr. Meth. A 369 169-179 (1996)

  16. Monte Carlo Simulation of MACS Y. Qiu and C. Broholm to be published (2000)

  17. Resolution: Analytical and Monte Carlo simulations. Y. Qiu and C. Broholm to be published (2000)

  18. Multiplexing crystal analyzer system Design by C. Brocker

  19. One of twenty channels “TAS” detector Collimator 1 Energy integrating Detector 8o vertically focusing Analyzer crystals BeO filter Be filter PG filter Design by C. Brocker Collimator 2

  20. Fixed vertical focusing of analyzers Double analyzer is “compound lens” efficient vertical focusing

  21. Constant energy transfer slice kf ki Q

  22. Assembling slices to probe Q-E volume 2 meV 1 meV 0 meV

  23. Projected data collection times CuHpCl • Powder sample Q-E map • 8 x 30 pts x 0.2 min. = 1:00 • Single crystal constant-E slice • 8 x 100 pts x 0.5 min. = 6:40 • Single crystal complete Q-E Volume • 8 x 100 x 10 pts x 0.5 min.= 3 days SCGO

  24. Scientific Program for NG0 spectrometer • Expanding the scope for Inelastic scattering from crystals: • 0.5 mm3 samples • impurities at the 1% level • complete surveys to reveal spin-wave-conduction electron interactions • extreme environments: pressure and fields to tune correlated systems • Probing short range order • solid ionic conductors, spin glasses, quasi-crystals, ferroelectrics, charge and spin polarons, quantum magnets, frustrated magnets. • Weak broken symmetry phases • Incommensurate charge, lattice, and spin order in correlated electron systems • Excitations in artificially structured solids • Spin waves in magnetic super-lattices • magnetic fluctuations in nano-structured materials

  25. Probing hole wave function in oxide : 1 D 2D? Y2-xCaxBaNiO5 Xu, Aeppli, Broholm, et al. Science (2000)

  26. NSF Share (50%) of the Construction of MACS $k Design Construction & Assembly Design & Construction Construction & Design Assembly & Commissioning

  27. Conclusions • Large solid angle access to NCNR cold source enables a unique cold neutron spectrometer. • MACS employs Bragg optics to focus the beam and provide > 108 n/cm2/s on the sample at 0.2 meV resolution. • The MACS detector concept offers the versatility, resolution, and low background of a TAS with 20 times greater data rate. • The highly efficient constant E mode of MACS will provide a unique capability for probing the structure of fluctuating systems. • MACS will be complementary to the DCS and future SNS TOF spectrometers because of its unique data collection protocol • NSF partnership is needed to realize the potential and make the unique capabilities available to widest possible cross section of the US scientific community