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					   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
                     •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
          CNCS Design Parameters
                                                            1




•    Ei = 0.8 - 50 meV




                                    dw (w = 0) (meV)
                                                        0.1

•    Variable resolution >10meV                                                              t = 32 ms

•    Minimum resolution dw~ 10meV                      0.01
                                                                                             t = 16 ms
                                                                                             t = 8 ms
                                                                                             IN5

•    Q ~ 0.1 to 4 Å-1
•    dQ < 0.02 Å-1                                              0   5   10     15
                                                                             E (meV)
                                                                                            20       25   30



•    Low Background                                    10
                                                            7




•   Capable of performing single                       10
                                                            6



    crystal experiments                    n/cm /s
                                                            5
                                                       10
                                       2




                                                            4                       8 ms
                                                       10
                                                                                    16 ms
                                                                                    32 ms
                                                                                    IN5
                                                            3
                                                       10
                                                                0       10                   20                30
                                                                             E (meV)
Scientific Focus
    •Quantum Liquids
    •Low Energy Inelastic Scattering
    •Quasi-elastic Scattering and Diffusion
    •Quantum Tunneling
    •Magnetism
    Instrument Development Team
Executive Committee         • Open Membership Policy
                               – Any interested parties can
• Paul Sokol – Penn State        join.
• Herb Strauss - Berkely    • Current Membership
                               – 12 National Labs
• Sow-Hsin Chen - MIT          – 18 University
• Meigan Aronson –          • Disciplines
                               –   Physics
  Michigan
                               –   Chemistry
• Hak Taub – Missouri          –   Nuclear Enginerreing
                               –   Materials Science
• Robert Dimeo – NIST
                               –   Polymers
                               –   Environmental Studies
                        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
               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
            Review – Jan 2002
  Build the highest performance spectrometer possible
  for the money available
   Cost                 Obvious - $9.7 M
                          •Data Rate – Flux on Sample x
                                         No. of Detectors
   Performance            •Sample Environment
                          •Reliability
                          •Maintainability
                          •Analizability
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
                             Results
• Incident Guide design              • Final Flight Path
   – Curved guide instead of            – Evaluating Shorter Flight
     bender                               Path
   – Fixed final funnel
                                     • Design
   – No Optics Carousel
                                        – Outsource Some Effort
       • Savings $700K
                                            • Building
• Choppers                                  • Final Flight Path
   – High speed                      • SNS/IDT demarcation
       • Pulse Shaping – Fermi
                                        – Inside/Outside building
       • Energy Selection – Double
         Disc – Al                      – Safety
   – Low Speed                       • Costs
       • Frame Overlap Only             – Consistent contingency
       • No T0 chopper – Future         – Common Cost Basis
         option
           – Savings $150K
Neutron Guide Configuration
                                                                                                  Choppers
Choppers
                       Pulse Shaping
                            Fermi @ 6.5 m
                       Energy Selection                                                                                 + Fermi Chopper +
                            Disc @ 37.8 m
                       Frame overlap
                            Disc @ 7.5m and 33m
                                                                                        Frame Overlap Choppers Transmission                         Dual Disc Transmission

                        10
                       10
                                                    Vitess internally generated
                       10
                            9                       Independently generated from ANL data

                            8
                       10

                            7
  Flux per unit area




                       10

                            6
                       10

                            5
                       10

                            4
                       10

                            3
                       10

                            2
                       10

                            1
                       10
                                0   1   2   3   4   5   6   7   8   9   10 11 12 13 14 15 16

                                                            time (ms)

                                            Flux From Moderator                                                 Transmission of Chopper Configuration


                                                                                               Design Reports – Mid April
                                                                                               Review by SAC
          Beam Line Shielding


•   Base
•   Front end
•   Stacked
•   Focusing optics
     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
          Instrument Shielding
• Wax cans
   – 6’x6’x8”
   – 1.25 tons
• Polyethylene?
• Seismic restraint
Alternate Final Flight Path
          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
                 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
           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         • SNS Time
    members                           – General User time
  – Reviewed Proposals                – Instrument Scientist
     • Program Continuity               Support (primary)
     • New Science
  – Rapid Access
  – Instrument Scientist (as part
    of IDT)
                 Comments
• Instrument Design
• Beam Time Allocation
• Sample Environment
  –   Displex
  –   Furnace
  –   Gas Handling
  –   Sample goniometer
• Others?

				
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posted:8/9/2012
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