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Cold Neutron Spectroscopy on MACS

Cold Neutron Spectroscopy on MACS. Collin Broholm Johns Hopkins University and NIST Center for Neutron Research. Virtues and limitations of INS Enhancing INS at the NCNR Description of MACS Science on MACS Integration of MACS in CHRNS Summary. Neutron Spectroscopy.

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Cold Neutron Spectroscopy on MACS

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  1. Cold Neutron Spectroscopy on MACS Collin Broholm Johns Hopkins University and NIST Center for Neutron Research • Virtues and limitations of INS • Enhancing INS at the NCNR • Description of MACS • Science on MACS • Integration of MACS in CHRNS • Summary

  2. Neutron Spectroscopy • A central tool in condensed matter physics • Unique information about dynamic correlations • Model independent access to interaction strength • Access microscopic structure of dynamic systems • Limited scope on current instruments • Need cm3 sized crystals • Need weeks of beam time • Need neutron scattering expert • Increased sensitivity will broaden impact • Comprehensive surveys to test theory • Parametric studies • Smaller samples

  3. Interesting samples come in all sizes Need high sensitivity to access physics in small samples Bound spinons in spin-1 chain Free spinons in spin-1/2 chain ≈ 10 mm ≈ 40 mm Y2BaNiO5 Cu(C4D4N2)(NO3)2 Bound spinons in spin-1/2 ladder Frustrated Magnetism ≈ 0.1 mm ≈ 4 mm ZnCr2O4 Cu2(quinox)2Cl4

  4. Resolution requirements to probe magnets Need range of E resolution at fixed Q resolution • QandEresolved spectroscopy: • Energy scale J varies more than length scalea

  5. Comparing TOF to TAS • Can focus neutrons with Bragg optics • Freely select range of energy transfer • Can use reactor CW flux TAS like • Large detector solid angle is possible • E-scan without moving parts • Can use spallation source peak flux TOF like

  6. TOF/TAS complementarity TAS Data from NIST 10% Ca doped TOF Data from MAPS/ISIS Y2BaNiO5 Xu et al science (2000)

  7. Unique Opportunities for INS at the NCNR 103F/F0 10-2 Steradian view of ≈ 250 cm2 cold source Brightness throughcooling

  8. Characteristics of a TAS at NG0 Ideal conditions for probing slowly propagating excitations in hard condensed matter • Wave vector resolution using full beam: • Energy Resolution: • Flux on sample: • Incident Energy Range 2.5-20 meV Collin Broholm NIM (1996)

  9. Maximizing the potential for new science • Beam delivery system • Focus full beam onto small sample • High rejection rate for non-Ei neutrons • Variable Q and Ei resolution • Detection system • Maximize solid angle of detection system • Offer variable resolution • Maximize S/N through shielding and geometry • User interface • Fast, accurate, and safe setup • Data Acquisition Planning Tools • Click for access to all features • Comprehensive visualization and analysis tools

  10. 40 channel detection system Sample position Aperture Attenuator Monitor Focusing supermirror Cold Source Cooled filters Variable Aperture Focusing monochromator on translation stage Shutter Radial Collimators Overview of MACS Shielding Helium 6.2 m

  11. MACS beam shutter • Four position rotating shutter • Closed: 70 mm thick neutron shielding • 50 mm vertical slit • Conical full opening • 100 mm vertical slit

  12. Cooled Incident Beam filters • Reject non-Ei neutrons • Ei< 5 meV : 10 cm beryllium • Ei<15 meV : 5 cm PG • Ei<20 meV : 8 cm Sapphire • Cold filters move in vacuum • Pneumatic actuation in <15 s

  13. The Monochromator Cask Doubly focusing monochromator Collimators to control E-resolution Aperture to control Q-resolution Translation Stage to vary incident energy

  14. Four-position Radial collimator • Control source size hence DE • Gd2O3 coated Stainless foils • Two aligned segments: 4 settings • Pneumatic actuation in <15 s Open 40’ 20’ 60’

  15. Variable incident beam aperture • Control beam envelope hence DQ • Independent control of Q-resolution • Trim beam to match monochromator • Full rangeactuation in 5 s • 10 cm moderating+absorbing shutters High density Polyethylene B4C 10 cm

  16. The MACS monochromator 357×4 cm2 PG(002) platelets with adjustable surface normal 35 cm 3×Hollow aluminum posts 45 cm 10B:Al shielding 10B:Al shielding Translation Stage Rotation Stage

  17. Worlds brightest neutron beam 6 5 F (108 n/cm2/s) 4 open 3 60’ 2 40’ 20’ 1 IN14 0 Y. Qiu and Y. Dong (2004)

  18. Collimators to vary resolution Cryo-filters to reduce background 20 × diffraction detectors 20 × double x-tal PG analyzers 20 × spectroscopic detectors 20+20 Channel MACS detection system

  19. The Double Crystal Analyzer Unit • Variable energy 2.5 meV<E<15 meV • Vertically focusing “compound lense” • Background suppressing collimator • Motion controlled by a single motor • Patent pending for Tim Pike’s design PG not yet mounted

  20. Multi Analyzer Crystal Spectrometer

  21. Constant energy transfer slice kf ki Q

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

  23. Data Acquisition Planning with DAVE • User indicates part of Q-E space to cover • Click and drag graphical input on Q-E space slices • DAVE generates script for optimal settings • Point spacing determined by calculated resolution • With full awareness of limits of motion • Reports actual volume covered • Script is executed by instrument control program • DAVE provides real time images of data

  24. Schreyer et al (2000) Matsunada et al. (2002) Saxena et al. (2000) Elements of Scientific Program for MACS • Expand the scope for Inelastic scattering from crystals: • 0.5 mm3 samples • Impurities at the 1% level • Extreme environments: pressure and fields to tune correlated systems • Complete surveys to reveal spin-wave-conduction electron interactions • Probing short range order • Solid ionic conductors, spin glasses, quasi-crystals, ferroelectrics, charge and spin polarons, quantum magnets, frustrated magnets. • Excitations in artificially structured solids • Spin waves in magnetic super-lattices • Magnetic fluctuations in nano-structured materials • Weak broken symmetry phases • Incommensurate charge, lattice, and spin order in correlated electron systems Lee et al. (2002) J. Rodriquez et al (2004)

  25. Funding MACS

  26. Building MACS Detection System (JHU@NIST) Sample positioning system (JHU@NIST) Monochromatic beam transp. (JHU@NIST) White Beam Conditioning System (NCNR) Monochromating system (JHU-IDG) Get Lost pipe (NCNR)

  27. Schedule for MACS

  28. Integration of MACS in CHRNS • Broad scientific impact requires CHRNS users • Partial support for 1 senior+2 junior scientists to operate MACS for users • Software development through DAVE • Amplify the MACS educational program through the CHRNS summer school • Partial support of maintenance • Miscellaneous repairs and upgrades • Computer hardware and software • Distribution of beam time • 20% NIST • 20% JHU • 60% CHRNS users

  29. Summary • MACS makes use of unique aspect of the NBSR: large solid angle access to intense cold neutron source • MACS will be a formidable tool to probe nano-scale dynamics in hard condensed matter • Most intense cold neutron beam in the world • Multi-channel low background detection system • seamless access to advanced features through DAVE • Ability to tailor energy range and resolution makes MACS complementary to TOF spectrometers • An active user program through CHRNS is needed to realize the scientific potential of MACS

  30. Contributors to MACS project NIST Center for Neutron Research: G. Baltic, P. C. Brand, C. Brocker, M. English, P. D. Gallagher, C. J. Glinka, P. Kopetka, J. G. LaRock, J. W. Lynn, J. Moyer, N. Maliszewskyj, D. J. Pierce, M. Rowe, J. Rush, and others Johns Hopkins University: R. Barkhouser, C. Broholm, R. Hammond, P. K. Hundertmark, R. Lavender, J. Orndorff, T. D. Pike, G. Scharfstein, S. A. Smee, and others

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