Page 91 - ILL Annual Report 2019

liquid N2
incident beam
The cryomagnet is used on the IN22 three-axis spectrometer in the elastic mode with no modification
to the spectrometer required. The sample is usually oriented with a crystallographic axis parallel or slightly misaligned to the horizontal magnetic field, to reach
the most interesting part of the reciprocal space.
Neutron pulses are recorded with a digital data
recorder measuring the generator voltage and current and the voltage on the pick-up coil. After correction for the neutron time of flight, the field dependence of the neutron intensities at each momentum transfer is extracted by summing the data accumulated over a few identical pulsed-field shots, with either constant time- or constant field-integration windows.
Several experiments have already been carried out successfully [2], and experience shows that about 40 pulses are sufficient to measure variation in the intensity of a Bragg peak with a field of
up to 40 T, i.e. about 6 hours, providing that V[mm3] x (m[μB/at]/v0[Å3])2 > 3.2 x 10-4, with
V the sample volume and m and v0, respectively, the moment and volume of the unit cell.
Figure 2
Photo of a sample glued onto the end of the sapphire holder. The thermal expansion of He is performed at the end of the brown Torlon tube in which helium circulates, against the flange of the sapphire sample-holder.
liquid He
≈1.5 K He
N2
sapphire
Torlon
Figure 1
MODERNISATION PROGRAMMES AND TECHNICAL DEVELOPMENTS
88-89
to He pump
scattered beam
Overview of the tail of the 40 T cryomagnet. The coil is immersed in liquid nitrogen and the sample is fixed to the end of a cold finger made of sapphire.
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