Page 90 - ILL Annual Report 2019

TECHNICAL AND COMPUTING DEVELOPMENTS
Fabienne Duc. French
High Magnetic Field National Laboratory of Toulouse, France
‘I am a CNRS scientist actively involved since 2006 in projects combining high-pulsed magnetic fields with X-ray and neutron scattering techniques. In particular, I am
responsible for the 30 T and 40 T pulsed-field generators used, respectively, for X-ray absorption spectroscopy measurements and neutron diffraction; and for assisting synchrotron and neutron users in their experiments. My research interests are magnetic field-induced phases in strongly correlated electron systems (magnetic quantum spin systems and heavy fermions).’
40 Tesla pulsed-field cryomagnet for single-crystal neutron diffraction
The CEA-Grenoble, the LNCMI-Toulouse and the ILL have together developed a
40 T pulsed-field cryomagnet for neutron diffraction, featuring an unprecedented duty cycle of 28 sec per day at 30 T
and 16 sec per day at 40 T. The sample temperature can be regulated at between 2 and 300 K, independently of the generation of the pulsed fields. The magnet can be made available to users within the framework of a collaboration between
the CEA-Grenoble (which runs the CRG triple-axis IN22 instrument at the ILL) and the LNCMI-Toulouse, which produced the coil and its 1.15 MJ mobile generator.
AUTHORS
F. Duc (High Magnetic Field National Laboratory of Toulouse, France) F. Bourdarot (ILL and CEA Grenoble, France)
E. Lelièvre-Berna (ILL)
ARTICLE FROM
Rev. Sci. Instrum. (2018)—doi: https://doi.org/10.1063/1.5028487
REFERENCES
[1] F. Duc, X. Fabrèges, T. Roth et al., Rev. Sci. Instrum. 85 (2014) 053905 [2] W. Knafo, F. Duc, F. Bourdarot et al., Nat. Commun. 7 (2016) 13075
In order to perform experiments in static fields greatly exceeding 15 T (vertical field) or 17 T (horizontal field), the CEA-Grenoble, the LNCMI-Toulouse and the ILL have designed and constructed the first long-duration and high duty-cycle pulsed-field cryomagnet producing a maximum horizontal field of 40 T for neutron diffraction. Compared with preceding systems, this magnet offers a much increased pulse duration and higher angular access in the scattering plane, thanks to conical openings of ±15 ° and ±30 ° upstream and downstream of the sample.
The coil, designed and built by the LCNMI-Toulouse, possesses a rapid-cooling technique by which liquid nitrogen cooling channels are directly inserted into the winding. To ensure high mechanical strengths, CuAg wire reinforced with Zylon was wound onto a coil body of glass fibre-epoxy composite (G10), which was itself placed around a highly non-magnetic, 1 mm-thick, double-cone of AISI 304L stainless steel. Using the 1.15 MJ transportable power supply developed at the LNCMI-Toulouse [1], the coil produces a maximum pulsed field of 40 T, with a rise time of 23 ms and a total duration of more than 100 ms every
9 min. The time between pulses is reduced at lower fields: every 7 min and 5 min, at 36 T and 31 T, respectively.
The coil is installed horizontally inside a cryostat developed by the ILL. A large, centrally placed, liquid nitrogen bath surrounded by a liquid helium jacket ensures that the coil can easily be replaced and cooled (figure 1). The initial cool-down time is 2.5 hours. The main current leads are fixed on one side of the coil,
the heat exchanger on the opposite side along the upper surface of the cone onto which the coil is wound (scattered beam side). To avoid eddy currents and minimise the neutron background, the heat exchanger is made of Torlon and sapphire (figure 2). The sample
is glued onto a holder also made from single crystalline sapphire and introduced into the heat exchanger. The maximum sample volume available is 8 x 6 x 6 mm3 and the cool-down time to 2 K does not exceed 30 min.
ANNUAL REPORT 2019