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The Cold Neutron Chopper Spectrometer

The Cold Neutron Chopper Spectrometer. Paul Sokol, Penn State University -- PI M. Aronson (Michigan), S.-H. Chen(MIT), R. Dimeo(NIST), H. Strauss(Berkely), H. Taub(Missouri). http://sokol.phys.psu.edu/CNCS. The Spallation Neutron Source. Cold Neutron Chopper Spectrometer. Range 1-50 meV

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The Cold Neutron Chopper Spectrometer

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  1. The Cold Neutron Chopper Spectrometer Paul Sokol, Penn State University -- PI M. Aronson (Michigan), S.-H. Chen(MIT), R. Dimeo(NIST), H. Strauss(Berkely), H. Taub(Missouri) http://sokol.phys.psu.edu/CNCS

  2. The Spallation Neutron Source

  3. Cold Neutron Chopper Spectrometer • Range • 1-50 meV • Resolution • 10-100 meV • Incident Flight Path • 37.5 M • Bender to move beam out of line of sight • Two high speed choppers to define E • Final Flight Path • ~3.5 M • +140o in scattering plane • +40o out of scattering plane

  4. CNCS Design Parameters • Ei = 0.8 - 50 meV • Variable resolution >10meV • Minimum resolution dw~ 10meV • Q ~ 0.1 to 4 Å-1 • dQ < 0.02 Å-1 • Low Background • Capable of performing single crystal experiments

  5. Scientific Focus • Quantum Liquids • Low Energy Inelastic Scattering • Quasi-elastic Scattering and Diffusion • Quantum Tunneling • Magnetism

  6. Executive Committee Paul Sokol – Penn State Herb Strauss - Berkely  Sow-Hsin Chen - MIT Meigan Aronson – Michigan Hak Taub – Missouri Robert Dimeo – NIST Open Membership Policy Any interested parties can join. Current Membership 12 National Labs 18 University Disciplines Physics Chemistry Nuclear Enginerreing Materials Science Polymers Environmental Studies Instrument Development Team

  7. Goals • World Class Spectrometer • Data Rate – Flux x Detectors • Sample Environment • Reliability/Maintainability • Analyzability – ability to produce papers (addressed in future) • Secondary concerns • Energy/Q range – Important – but small changes not crucial • Resolution - ditto

  8. IDT Meeting CNCS Workshop - NIST May 21-22, 2001 • 30 attendees • Instrument Scientists - Mezei, Bewley, Copley, Cook… • Engineers - Fornek, Strons, Berker, Brandt… • Scientists - Magnetism, Quantum Liquids, Tunneling, diffusion, Biological systems, … Results • Large detector coverage • -Big simple tank costs just as much as smaller complicated tank • -Room for future expansion • 37.5 m initial flight path-Instrument just outside building – satisfies scientific requirements while reducing cost • 3.5 m Final Flight path-more detectors without sacrificing scientific goals

  9. Build the highest performance spectrometer possible for the money available Review – Jan 2002 Cost Obvious - $9.7 M • Data Rate – Flux on Sample x • No. of Detectors • Sample Environment • Reliability • Maintainability • Analizability Performance Neutron Design – performance and resolution of instrument Lechner, Copley, Carpenter, Cook, Neuman Conventional Design – Engineering effort for flight paths Laman, Brandt, Brocker, Linzell Components – Choppers, Detectors, Electronics, etc. Broholm, Adams, Cook, Santadonato Installation – Building, assembly at ORNL Gallagher, Bohringer

  10. Incident Guide design Curved guide instead of bender Fixed final funnel No Optics Carousel Savings $700K Choppers High speed Pulse Shaping – Fermi Energy Selection – Double Disc – Al Low Speed Frame Overlap Only No T0 chopper – Future option Savings $150K Final Flight Path Evaluating Shorter Flight Path Design Outsource Some Effort Building Final Flight Path SNS/IDT demarcation Inside/Outside building Safety Costs Consistent contingency Common Cost Basis Results

  11. Neutron Guide Configuration

  12. Choppers • Choppers • Pulse Shaping • Fermi @ 6.5 m • Energy Selection • Disc @ 37.8 m • Frame overlap • Disc @ 7.5m and 33m + Fermi Chopper + Frame Overlap Choppers Transmission Dual Disc Transmission Flux From Moderator Transmission of Chopper Configuration Design Reports – Mid April Review by SAC

  13. Beam Line Shielding • Base • Front end • Stacked • Focusing optics

  14. Final Flight Path Chamber • Contains argon • Pressure at ~1” of water • Similar to glove box • Supports heavy load on top • Personnel & equipment • Hydrogenous shielding • Allows access to detectors • Detectors in chamber (no window) • Extent of accessibility

  15. Instrument Shielding • Wax cans • 6’x6’x8” • 1.25 tons • Polyethylene? • Seismic restraint

  16. Alternate Final Flight Path

  17. Alternate Building Design • Combine building and shielding • Similar to hutches for instruments at ISIS and LANSCE • More expensive building cost • No final flight path/shielding cost • Relative evaluation of costs is underway

  18. Detectors • 620 1m long, 2.54cm wide He3 Tubes in Horizontal plane • Small angle detector ? ±10o • Space to fill tubes • ±10-40o out of plane ±10-140o in plane • In Gas Tank • At 3.5 m from sample position

  19. Beam Time Allocation • Outside Users – 40% • IDT/SNS - 60% • Roughly 50-50 split (over 10 yrs) • Construction versus Operation • IDT Time • No Fixed Allocation for members • Reviewed Proposals • Program Continuity • New Science • Rapid Access • Instrument Scientist (as part of IDT) • SNS Time • General User time • Instrument Scientist Support (primary)

  20. C S C N Comments • Instrument Design • Beam Time Allocation • Sample Environment • Displex • Furnace • Gas Handling • Sample goniometer • Others?

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