Polarised 3 He Based Neutron Polarisers & Analysers for OPAL Instruments. W. T. Hal Lee, Frank Klose (ANSTO) Ken Andersen, David Jullien (ILL)

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1 Polarised 3 He Based Neutron Polarisers & Analysers for OPAL Instruments W. T. Hal Lee, Frank Klose (ANSTO) Ken Andersen, David Jullien (ILL)

2 Polarised 3 He Setup for 6 ANSTO Instruments To facilitate the use of polarised neutrons in scattering works, ANSTO will acquire a 3 He polarising station and instrument equipment (silicon spin filter cell, magic box, wide-angle analyser cell, Pastis coils, local filling setup, transporter, etc.)

3 Platypus Neutron Reflectometer Incident beam polariser Supermirror (installed) Scattered Beam Sample, Magnet Polarised Incident Beam Analyser requirements Wavelength bands 2-12 Å. 5.4 full-widthbeam divergence Ø130 mm cell cross-section Low noise generated by analyser Does not change beam divergence or direction Analyser RF flipper Polarizer mirror & RF flipper (Courtesy Frank Klose, Andrew Nelson, Michael James, ANSTO)

4 Quokka SANS Incident beam polariser Supermirror (installed) Scattered Beam Sample, Magnet Polarised Incident Beam Analyser requirements Wavelength band Å 4.7º full-width beam divergence Ø130 mm cell cross-section Low noise generated by analyser Does not change beam divergence or direction Analyser RF flipper Polarizer mirror & RF flipper (Upstream) (Courtesy Elliot Gilbert, Alain Brule, ANSTO)

5 WOMBAT High Intensity Diffractometer Incident beam polariser requirements Wavelength band 3-5 Å 8º full-width beam divergence (Focusing monochromator) Accepts beam cross-section 135 mm wide x 20 mm height Low noise generated by polariser Does not change beam divergence or direction Analyser requirements Wavelength band 3-5 Å Accepts 120º scattering angle and 50 mm height 16º full-width vertical beam divergence Accepts Ø50 mm sample environment Low noise generated by analyser Does not change beam divergence or direction Polarizer Polarised Incident Beam Sample, Magnet Wide- Angle Analyser (Courtesy Andrew Studer, ANSTO) Scattered Neutrons

6 Pelican Cold Neutron Time of Flight Spectrometer Incident polariser 3 polarising supermirror Analyser requirements Wavelength band 2-12 Å Accepts 120º scattering angle and 50 mm height 16º full-width beam divergence Accepts Ø100 mm sample environment Low noise generated by analyser Does not change beam divergence or direction Polarised Incident Beam Supermirror Polariser (upstream) Sample, Magnet Scattered Neutrons Wide- Angle Analyser (Courtesy Dehong Yu, ANSTO)

7 Sika Cold Neutron Triple-Axis Spectrometer Incident beam polariser requirements Wavelength band Å 4º full-width beam divergence Ø130 mm cell cross-section Low noise generated by polariser Does not change beam divergence or direction Analyser requirements Wavelength band Å 8º full-width beam divergence Ø130 mm cell cross-section Low noise generated by analyser Does not change beam divergence or direction Polariser Polarised Incident Beam Cylindrical Analyser Sample, Magnet or Scattered Neutrons (Courtesy Eno Imamovic, SIKA Team) Wide-Angle Analyser

8 Taipan Thermal Triple-Axis Spectrometer Incident beam polariser requirements Wavelength band 1-4 Å 4º full-widthbeam divergence Ø130 mm cell cross-section Low noise generated by polariser Does not change beam divergence or direction Analyser Polariser Analyser requirements Wavelength band 1-4 Å 8º full-widthbeam divergence Ø130 mm cell cross-section Low noise generated by analyser Does not change beam divergence or direction Scattered Neutrons Sample, Magnet (Courtesy Sergey Danilkin, ANSTO) Polarised Incident Beam

9 Workshop on Polarised Neutron Scattering at ANSTO (28-29 November 2007) 3 He Heusler Supermirror (transmission) 1 Wavelength / Energy range and bandwidth Epithermal to very cold. Works with monochromation or TOF. Wide bandwidth. Lower transmission for cold neutrons. Can tune to appropriate wavel ength/energy. High flipping-ratio (comparabl e Figure of Merit with Heusler) with appropriate gas pressure / cell thickness 5 mev (4 Å) mev (0.9 Å). Monochromation technique. Narrow bandwidth. Energy range & resolution ~ PG 002. Transmission / Reflectivity of npolarised beam Up to 0.4, wavelength dependent, virtually independent of beam divergence.. Up to 0.4, depend on the wavelength, Heusler crystal mosaic and beam divergence Up to 0.4, mild dependence on wavel ength over working range, limited beam divergence. Divergence, Angular span, Focusing beam Accepts high divergence. Covers wide angular span. Works with focusing beam. Too well collimated. Use many mirrors to cover the angles. Focusing works in one direction Beam direction Uniformity Preparation and Operation Does not change beam direction Polarisation uniform across large beam 1 h to set up and do calibration. 15 min every h to exchange gas and check polarisations hour relaxation of polarisation. Accepts high divergence. Reposition to different angle. Energy-angle coupled. Focusing works in one direction Change beam direction Polarisation and transmission may vary Can changed to polarised in automated way. Setup once, calibrate occasionally Does not change beam direction Polarisation and transmission may vary Can changed to polarised in automated way. Setup once, realign occasionally Maintenance Filling station maintenance Zero maintenance. Zero maintenance. Sensitivity to interference To magnetic fi eld gradients. Magnetic shielding needed. Insensitive Insensitive Flipping ratio 2.3 Å (15 mev) to cold. Work with monochromation or TOF. Wide bandwidth. Lower transmission for cold neutrons. 0.8 Polaris ation P Transm iss ion T 0.6 Figure-of -Merit P T High flipping ratio (comparable Figure of Merit with 3 He) High flipping ratio for cold neutrons. Low flipping ratio for thermal neutrons Wave len gth (A) Supermirror M a g n e ti ze d H eu s le r - u n p o la r is ed b ea m 0.5 λ = 3 Å λ = 1. 8 Å λ = 1Å FW H M m o s a i c (d e g re e s ) 0.8 Heusler alloy Polarised 3He A decision was made to purchase a turn-key MEOP system together with the beam instrument equipment cells, field coils, transporter, local-filling setup, and diagnostic devices from the Institute Laue-Langevin. 1

10 Polarising 3 He by Metastable Optical Pumping Method Colegrove, et. Al., Phys. Rev. 132:6 (1963) A small amount (mbar in pressure) of 3 He gas is released into the optical pumping cells He nuclei polarised by Metastable Exchange optical Pumping Method. 1) Electrical discharge excite the 3 He atom from the 1 1 S 0 to the 2 3 S 1 excited state. 2) 1083 nm circularly polarised σ + laser drive the transition from one of the spin-state 2 3 S 1 (M F = -1/2) to 2 3 P 0 (M F = +1/2) state. 3) Spontaneous emission returns the atom from 2 3 P 0 equally to both sublevels of 2 3 S 1. As the depletion of 2 3 S 1 (M F = -1/2) state continues, a high population of the 2 3 S 1 (M F = +1/2) state results. 4) The atoms in the ground state are polarised by metastability exchange collisions between atoms in the ground state and atoms in the 2 3 S 1 (M F = +1/2) state. 5) Through hyperfine interaction, the nuclei 3 He are polarised. 3. A polarisation-preserving compressor compresses the polarised gas into a buffer cell. And the cycle starts again until the targeted polarised gas pressure is reached. Magnetic Field Coil ILL MEOP System Tyrex (Photo Courtesy Ken Andersen, ILL) Optical Pumping Cells

11 Polarising 3 He by Metastable Optical Pumping Method Colegrove, et. Al., Phys. Rev. 132:6 (1963) A small amount (mbar in pressure) of 3 He gas is released into the optical pumping cells. 2. ILL 3 He Tyrex: nuclei polarised by Metastable Exchange optical Pumping Method. 80% 3He polarisation in neutron spin-filter cell 1) Electrical discharge excite the 3 He atom from the 1 1 S 0 to the reached. 2 3 S 1 excited 1 bar-liter, state. 4 hours. 2) 1083 nm circularly polarised σ + laser drive the transition from one of the spin-state 2 3 S 1 (M F = -1/2) to 2 3 P 0 (M F = +1/2) state. Trade-off: 3) Spontaneous emission returns the atom from 2 3 P 0 equally to both sublevels of 2 3 S 1. As the depletion of 2 3 S 1 (M F = -1/2) state continues, a high population of the 2 3 S 1 (M F = +1/2) state results. Faster production Lower polarisation 4) The atoms in the ground state are polarised by metastability exchange collisions between atoms in the ground state and atoms in the 2 3 S 1 (M F = +1/2) state. 75% 3He polarisation, 1 bar-liter/ hour. 5) Through hyperfine interaction, the nuclei 3 He are polarised. 3. A polarisation-preserving compressor compresses the polarised gas into a buffer cell. And the cycle starts again until the targeted polarised gas pressure is reached. Magnetic Field Coil ILL MEOP System Tyrex (Photo Courtesy Ken Andersen, ILL) Optical Pumping Cells

12 ANSTO MEOP Polarising Station Performance: 1 bar-liter/hour >70% polarisation in spin-filter cell Up to 3 bars in pressure Setup: 6 optical-pumping cells, 3 lasers 2.4 m diameter, 2.8 m tall

13 ANSTO MEOP Polarising Station MEOP polarising station MEOP polarising station CG1 CG3 CG3 CG1 At ANSTO, we are preparing a laboratory area on top of the neutron guide bunker to house the MEOP polarising station.

14 ANSTO MEOP Polarising Station MEOP polarising station CG3 MEOP polarising station CG1 CG1 CG3 Lab area At ANSTO, we are preparing a laboratory area on top of the neutron guide bunker to house the operation of the MEOP polarising station.

15 Polarising and Transporting 3 He To An Instrument 3 He polarised in a MEOP station. Then transferred to a holding cell and placed in a transporter. Holding cell carried in transporter to the instrument Polarized 3 He transferred into container

16 Using Polarised 3 He Neutron Polariser/Analyser Setup for reflectometer, SANS, and triple-axis spectrometer Magic Box Polarised 3 He in glass cell Silicon window cell 3 He polarization = 75% Cell pressure x length =10 bar- cm Silicon window thickness = 4 mm/window Setup for wideangle analysis for diffractometer, triple-axis spectrometer Uniform 3D Magnetic field coils Neutron Polarised 3 He in glass cell Neutrons Sample in refrigerator Polarization/Analysing Efficiency P, Transmission T P T N (unpolarized) T- (spin-down) T+ (spin-up) Physica B , 1142 (2006) Wavelength (A)

17 Using Polarised 3 He Neutron Polariser/Analyser Setup for reflectometer, SANS, and triple-axis spectrometer Magic Box Polarised 3 He in glass cell Silicon window cell 3 He polarization = 75% Cell pressure x length =10 bar- cm Silicon window thickness = 4 mm/window Setup for wideangle analysis for diffractometer, triple-axis spectrometer Uniform 3D Magnetic field coils Neutron Polarised 3 He in glass cell Neutrons Sample in refrigerator Polarization/Analysing Efficiency P, Transmission T P T N (unpolarized) T- (spin-down) T+ (spin-up) Physica B , 1142 (2006) Wavelength (A)

18 Using Polarised 3 He Neutron Polariser/Analyser Setup for reflectometer, SANS, and triple-axis spectrometer Magic Box Polarised 3 He in glass cell Silicon window cell 3 He polarization = 75% Cell pressure x length =20 bar- cm Silicon window thickness = 4 mm/window Setup for wideangle analysis for diffractometer, triple-axis spectrometer Uniform 3D Magnetic field coils Neutron Polarised 3 He in glass cell Neutrons Sample in refrigerator Polarization/Analysing Efficiency P, Transmission T P T N (unpolarized) T- (spin-down) T+ (spin-up) Physica B , 1142 (2006) Wavelength (A)

19 Magic Box at Quokka SANS Magic Box SANS Detector Scattered Beam Sample, Magnet Polarised Incident Beam Magic Box SANS Detector Analyser RF flipper Polarizer mirror & RF flipper (Upstream) The polarised 3 He cell and the magic box Will be lowered into the beam when used Polarised 3 He is filled using local filling from the outside Lift out of the way of the detector when it is not used. ANSTO s investment in the design, construction, and operation of infra-structures for using polarised 3 He.

20 Equipment List Equipment provided by ILL Item Item Quantity 3 He gas polarising MEOP station: 1 bar-litre/hour, >70% 3He polarisation in the spin-filter 1 filter cell, up cell, to up 3 bars to 3 in bars the in spin-filter the spin-filter cell cell 3 He gas (bar-liter) 25 Cylindrical 3 He cells (large and small) 11 Wide-angle analyser cells (120º coverage) 4 Magic box with RF coils 5 PASTIS coils 2 Transporters (large and small) 3 Local-filling system (buffer cell, dry pump, glassware) 1 Polarisation preserving capillary (metre) 14 RF power supply 5 DC power supply 24 NMR system 4 Equipment provided by ANSTO Item Integration components for instruments: guide fields, vacuum fit-through (if needed), etc. Polarised 3 He lab on top of neutron guide bunker

21 Integration and Test on instruments Components for 2 instruments ready for installation and test on 1/7/11 Commission at all 6 instruments by 30/6/ Qtr 1 Qtr 2 Qtr 3 Qtr 4 Qtr 1 Qtr 2 Qtr 3 Qtr 4 Qtr 1 Qtr 2 Qtr 3 Quokka Platypus Wombat Pelican Sika/Taipan 3 He Polarising station arrives

22 Summary ANSTO will acquire a MEOP system from the ILL to provide polarised 3 He for neutron scattering work. Instrument Platypus Reflectometer Quokka SANS Wombat - High resoultion diffractometer Pelican - Cold Neutron Time-Of-Flight Spectrometer Sika - Cold neutron Triple-Axis Spectrometer Taipan - Thermal Triple-Axis Spectrometer Plan supermirror / 3 He supermirror / 3 He 3 He / 3 He Heusler / 3 He 3 He / 3 He 3 He / 3 He Current supermirror / none supermirror / none none / none supermirror / none none / none none / none ILL: 3 He polarising station: Work is underway to purchase the main components. Instrument equipment: Preliminary design completed. ANSTO: Designing & building guide field and instrument-specific infrastructure components. Survey & designing lab platform to house the operation of the MEOP station. ANSTO project Lead has commenced at the ILL. Delivery of the polarising station & instrument equipment are expected in June 2011.

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