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Polarisers & Flippers

With Cryopad, you solve complex magnetic structure problems that were intractable when employing other techniques. Now, you can also investigate slow magnetic relaxations using the novel Polarimetric Spin-Echo technique.

Have you tried spin polarised powder diffraction on D20 with Cryopol ?

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Polarimetry

Cryogenic Flippers/Polarisers

We propose two cryogenic devices for polarising the beam and flipping the neutron polarisation. The first one, called Cryopol for 'Cryogenic Polariser', is owned by the CEA and made available by the CEA-CRG team on request. The second one called Cryopol-II is a new cryogen-free version able to host much larger spin filter cells. Both consist of a superconducting Nb cylinder in which we trap a 8G homogeneous magnetic field upon cooling.

The second-generation Cryopol (i.e. Cryopol-II) has recently be commissioned on D20 for measuring magnetisation distributions in nano-scale and molecular magnets featuring weak magnetisation and anisotropy. Our colleagues from the Neutron Optics team have constructed very large spin filter cells covering the full section of the beam (6 x 20 cm2 at the cell position) and accepting pressures up to 3 bar. We have designed and constructed a special nutator that flips and transports adiabatically the neutron polarisation with better than 99% efficiency at the exit of Cryopol-II. The neutron beam polarisation is continuously recorded with two monitors located before and after Cryopol-II (see function Efficiency2).


Code
Magnetic
field (G)
Flipping
efficiency
Spin filter cell
volume (mm)
3He spin
relaxation
Diameter
(mm)
Year
Type, Comment
Cryopol-I
(CEA)
8
>99.9%
above 0.4Å
Ø60 x 100
60 hours
at 2.6 bar
ů320 in
scat. plane
2001
Bottom loading
Cryopol-II 8
>99.9%
above 0.4Å
80 x 220 x 100
(W x H x D)
100 hours
at 1.2 bar
ů320 in
scat. plane
2008
Bottom loading,
cryogen-free