Polarized Neutrons in ANSTO – From LONGPOL to Pelican, Taipan, Sika, Platypus and Quake
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Transcript of 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)
Location/ beamtube
6HGR9 @ HIFAR, radial tube with =5.9 mm
Monochromator
Velocity selector with =3.6 Å & =13 %
• Polarizer & Analyzer
Iron Filters with t =6 mm in H =1 T, P =33 %
• Spin flipper
R-F coil with =0.5 MHz in H =17 mT, =98 %
• Detector
4 x =2” BF3 tubes (RSN 44A) in parallel
Initial purpose: studies of magnetic diffuse (static) scattering
Design criteria: separate magnetic & nuclear components,high intensity, low ‘q’ resolution
LONGPOL – Later Development
Primary Shutter
Reactor Face
Pyrolytic GraphiteMonochromators
Neutron Shielding
Secondary Shutter
Analysers
Detectors
Polarizer
Spin Flipper
Sample
Monitor
Primary Shutter
Reactor Face
Pyrolytic GraphiteMonochromators
Neutron Shielding
Secondary Shutter
Primary Shutter
Reactor Face
Pyrolytic GraphiteMonochromators
Primary Shutter
Reactor Face
Primary Shutter
Reactor Face
Primary Shutter
Reactor Face
Primary Shutter
Reactor Face
Primary Shutter
Reactor Face
Pyrolytic GraphiteMonochromatorsPyrolytic GraphiteMonochromators
Neutron Shielding
Secondary Shutter
Secondary Shutter
Secondary Shutter
Analysers
Detectors
Polarizer
Spin Flipper
Sample
Monitor
Analysers
Detectors
Polarizer
Spin Flipper
Sample
Monitor
Analysers
Detectors
AnalysersAnalysers
DetectorsDetectors
Polarizer
Spin Flipper
Sample
Monitor
Polarizer
Spin Flipper
Sample
Monitor
Polarizer
Spin flipper
LONGPOL – Energy Analysis
Flipper drive pulse sequence
Intensity variation for non-spin-flip scattering
Intensity variation for spin-flip scattering
Cross-correlation of intensity with drive sequence
• Direct separation of spin-flip and non-spin flip scattering.
• TOF – energy analysis
Modulation of neutron polarization using pseudo-random pulse train to drive spin flipper, Cross-correlation of intensity with the drive sequence
LONGPOL - Science
• Served for more than 30 years• Produced important scientific studies including:
spin glass nature of Cu95Mn5
short range order in -MnNi flux relaxation in high Tc superconductorscrystal field transitions in PrAl3
magnetic phase of Fe2MnSi
magnetic domains in amorphous Fe-Zr
Lessons from LONGPOL
• Fix Geometry means non-flexibility• Compact design means
Difficulty to accessLimitation to different sample environment
• Low flux, long data acquisition time• Statistic chopper
Relative high backgroundOnly works well for strong signals
New Instruments in OPAL
Wombat (HIPD)Kowari (RS) Echidna (HRPD)
Koala (QLD)
Platypus (Ref)
Quokka (SANS)
Taipan (TAS)Sika (CTAS)
Pelican (TOFPAS)
Pelican - TOFPAS
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 goalsNeutron 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)
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)
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.
5.4 metre
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: E/Ei = 2.5% (50µeV to 300 µeV)
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)
Polarization Analysis
n
n
S p i n s p l i t t e r C o l l i m a t o r
P o l . S u p e r m i r r o r
G d
S i
n
n
Budget Estimation – Stage 2
Item Cost (A$ K)
Sub-total Stage 2 Capital 4,792
HR 789
Running 254
Total estimate for stage 2Contingency (20%)
5,8351,167
Total 7002
Project Schedule
Stage 1: Front End
Monochromator shield, stage and dance floor
Stage 2: Whole Instrument
2005 2006 2007 2008 2009
Schedule:Standard components
(stage 1)
Conceptual design
Engineering design
Manufacture & procure
Assemble & install
Commissioning
-TAS
Incident E: 5 meV – 120 meVEnergy Transfer: up to 80 meVScattering angle 2Өm: 15o – 85o
Analyzer scattering angle 2ӨA : -110o – 110o
Double focusing Mono. and Analyzer.
TOF-Neutron Reflectometer
Horizontal sampleSolid –solidLiquid – solidPolarization option
Transmission Polarizer – Ref. and SANS
iron yoke
adsorbing borated glass
(Non-magnetic) m=3 supermirrors
Permanent magnets
50 mmElevation looking along the beam
(m=3) FeSi polarizing supermirror
on both sides of thin Si wafers
Elevation perpendicular to the beam
1200 mm
= 3 to ~17 ÅRF spin flippers before & after sample
Sample environments
Cryo-free cryo-furnace
4 K 800 KArrived
One system is commissioned
Liq. He cryostat
1.4 K 300 K
Arrived
3He cryostat insert ~300
mK
Dilution refrigeration ~30 mK
7.4 Tesla cryo-free cryo-magnet
Commissioned in ANSTO
5 Tesla cryo-free cryo-
magnet (N.Z. design for
Reflectometry/SANS)
Under design
HMI’s 15 Tesla cryomagnet.
Proposed
TOFPAS - (Q,ω)
TOF-PAS
Sika
Taipan
Heavy fermions
Molecular & lattice
vibrations
Critical scattering
Spin waves
Molecular rotations