The WAVE Neutron magnet is an innovative instrument developed for neutron diffusion experiments as part of a collaboration between DSM/IRAMIS/LLB and DRF/IRFU/SACM. It is designed for installation in the experimental areas of the Léon Brillouin Laboratory at the Orphée reactor in CEA-Saclay.
PERFORMANCE REQUIRED BY USERS
LLB physicists have expressed the following performance requirements: the magnet must create a magnetic field capable of varying continuously from 0 to 1 tesla; it must be “steerable” in all three spatial directions; it must be homogeneous to better than 1000 ppm throughout the sample volume, which is a sphere of 5 mm radius (sample interaction zone). The space must remain accessible to the neutron detectors within a 75 mm area on either side of the equatorial plane, and at an angle covering 110° on either side of the incident beam axis in this plane.
Samples analyzed by diffraction come in their own cryostat which must be inserted into the core of the WAVE magnet from above. A central sample well with a warm diameter of at least 100 mm must be provided for this purpose.
These conditions are obtained by the design patented in 2012. A pair of coils known as Helmholtz's (in green on the 3D view), arranged horizontally on either side of the equatorial plane and centered on the sample well, generate the vertical component of the magnetic field. They are shielded by two compensating coils. Note that these shielding coils also contribute to field homogeneity around the sample. The horizontal component of the field is created by the leakage fields emanating from 12 coils that are arranged on two hexagons (one at the top and one at the bottom) and supplied in opposition.
The 16 solenoids are wound with a 0.68 mm x 1.08 mm NbTi superconductor, impregnated and embedded in aluminum casing. This casing is cooled indirectly by liquid helium circulating in a thermosiphon, the reservoir of which acts as a phase separator and is cooled by a cryogenerator, according to the “termautonome” principle studied at SACM. The WAVE coils are powered by four independent 200 A power supplies through HTS current leads. They are protected by cold diodes. The cryostat is shown opposite together with all the other equipment.
THE WAVE NEUTRON MAGNET
The magnet was ordered turnkey from the company Sigmaphi and is scheduled for delivery to Saclay in June 2017. The project is supported by the Ile-de-France Region through the NanoK-2014-ML-005 Grant.