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Polarized Neutrons in ANSTO – From LONGPOL to Pelican, Taipan, Sika, Platypus and Quake

Polarized Neutrons in ANSTO – From LONGPOL to Pelican, Taipan, Sika, Platypus and Quake. Dehong Yu and Shane Kennedy Bragg Institute, ANSTO, Australia. LONGPOL ( 1973-~1980). Initial purpose: studies of magnetic diffuse (static) scattering Design criteria:

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Polarized Neutrons in ANSTO – From LONGPOL to Pelican, Taipan, Sika, Platypus and Quake

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  1. Polarized Neutrons in ANSTO – From LONGPOL to Pelican, Taipan, Sika, Platypus and Quake Dehong Yu and Shane Kennedy Bragg Institute, ANSTO, Australia

  2. LONGPOL (1973-~1980) • Initial purpose: • studies of magnetic diffuse (static) scattering • Design criteria: • separate magnetic & nuclear components, • high intensity, • low ‘q’ resolution • Location/ beamtube • 6HGR9 @ HIFAR, radial tube with f =5.9 mm • Monochromator • Velocity selector with l =3.6 Å & dl/l =13 % • Polarizer & Analyzer • Iron Filters with t =6 mm in H =1 T, P =33 % • Spin flipper • R-F coil with n =0.5 MHz in H =17 mT,  =98 % • Detector • 4 x f =2” BF3 tubes (RSN 44A) in parallel

  3. Polarizer Spin flipper LONGPOL – Later Development

  4. Flipper drive pulse sequence Intensity variation for non-spin-flip scattering Intensity variation for spin-flip scattering Cross-correlation of intensity with drive sequence LONGPOL – Energy Analysis Modulation of neutron polarization using pseudo-random pulse train to drive spin flipper, Cross-correlation of intensity with the drive sequence • Direct separation of spin-flip and non-spin flip scattering. • TOF – energy analysis

  5. LONGPOL - Science • Served for more than 30 years • Produced important scientific studies including: • spin glass nature of Cu95Mn5 • short range order in g-MnNi • flux relaxation in high Tc superconductors • crystal field transitions in PrAl3 • magnetic phase of Fe2MnSi • magnetic domains in amorphous Fe-Zr

  6. Lessons from LONGPOL • Fix Geometry means non-flexibility • Compact design means • Difficulty to access • Limitation to different sample environment • Low flux, long data acquisition time • Statistic chopper • Relative high background • Only works well for strong signals

  7. Taipan (TAS) Echidna (HRPD) Wombat (HIPD) Koala (QLD) Sika (CTAS) Platypus (Ref) Kowari (RS) Quokka (SANS) New Instruments in OPAL Pelican (TOFPAS)

  8. Pelican - TOFPAS

  9. TOF-PAS Preliminary Specifications • Design goals: • Inelastic & quasi-elastic neutron spectroscopy • – time focusing TOF spectrometer (Comparable w/- IN6 @ ILL) + • Polarization analysis capability (Comparable w/- D7 @ ILL) • Preliminary Specs. – to reach the design goals • Neutron Wavelength: 2.4 Å – 6.3 Å, (14.2 meV – 2.1 meV) • Energy resolution: 50 µeV to 350 µeV (~2.5%) • Q range: 0.05 Å-1- 5 Å-1 • Solid angle: ¾ Steradians (non-pol), ¼ Steradians (pol) • Neutron flux at sample: ~ 8 x106 n/cm2/s at 3.7 Å, (full beam)

  10. Current Status - Stage 1 • Conceptual design finished,Dance floor installed • Monochromator stage ordered, Beam Monitor ordered • Monochromator shield arrived, Installation started 40° < 2Θ < 140°; 2.1 meV < Ei < 14.2 meV, (HOPG)

  11. 5.4 metre The TOF-PAS Dance floor The TOF-PAS granite dancefloor (area = 38 m2) -sufficient for 5m flight path from monochromator to detector over all possible take-off angles.

  12. Stage 2 • Phase 1 - Conceptual Design • General considerations • Multiple HOPG monochromator (vertical or double focusing), mosaic about 0.5o • Wavelength filter: Cold Beryllium filter for λ above 4.1 Å and a HOPG diffraction filter for λ < 4.1 Å. • Beam Chopper: Double Stage Fermi Chopper • Sample stage: standard A-Z system • Collimation system (after sample) • Detector: 250 PSD 3He tube (Φ = 12.5 mm and length = 1m), cover about ¾ Steradian (3.125 m2) • Spectrometer Tank: Vacuum or gas filled (He or Ar ?) • Energy resolution: DE/Ei = 2.5% (50µeV to 300 µeV)

  13. Polarization Analysis • Polarizer: Supermirror bender • Spin Flipper: Mezei flipper; • Analyzer: Supermirror bender, and 3He polarizing filter is also considered if it becomes available in ANSTO. • Guide field: to be designed Polarizing bender Analyzing bender: (8 elements)

  14. Polarization Analysis

  15. Budget Estimation – Stage 2

  16. Project Schedule • Stage 1: Front End • Monochromator shield, stage and dance floor • Stage 2: Whole Instrument • Schedule: • Standard components • (stage 1) • Conceptual design • Engineering design • Manufacture & procure • Assemble & install • Commissioning

  17. -TAS Incident E: 5 meV – 120 meV Energy Transfer: up to 80 meV Scattering angle 2Өm: 15o – 85o Analyzer scattering angle 2ӨA: -110o – 110o Double focusing Mono. and Analyzer.

  18. TOF-Neutron Reflectometer Horizontal sample Solid –solid Liquid – solid Polarization option

  19. Dl= 3 to ~17 Å RF spin flippers before & after sample (Non-magnetic) m=3 supermirrors iron yoke Elevation looking along the beam 50 mm Permanent magnets adsorbing borated glass Transmission Polarizer – Ref. and SANS 1200 mm (m=3) FeSi polarizing supermirror on both sides of thin Si wafers Elevation perpendicular to the beam

  20. 5 Tesla cryo-free cryo-magnet (N.Z. design for Reflectometry/SANS) Under design Cryo-free cryo-furnace 4 K  800 K Arrived One system is commissioned Liq. He cryostat 1.4 K  300 K Arrived 7.4 Tesla cryo-free cryo-magnet Commissioned in ANSTO HMI’s 15 Tesla cryomagnet. Proposed Sample environments • 3He cryostat insert ~300 mK • Dilution refrigeration ~30 mK

  21. TOF-PAS Taipan Sika TOFPAS - (Q,ω) Molecular & lattice vibrations Spin waves Heavy fermions Molecular rotations Critical scattering

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