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