Instrument description

The thermal neutron diffractometer D23 is devoted to single crystal measurements, either with unpolarized or polarized neutrons, in the incident wavelength range 1 - 3 Å. It can support large sample environments (pressure cells, up to 30 kbar, high field cryomagnets, up to 15 T, dilution fridges, …) and is characterized by a high flux and a very good signal over noise ratio. D23 is devoted to the determination of magnetic structures, magnetization density maps and magnetic phase diagrams, in high field and/or high pressure, and at low temperature.

D23 is a double-monochromator two-axis diffractometer with a lifting detector mounted in an arc. It is installed on the thermal neutron guide H25 which is equipped with a supermirror-coating. The guide is curved (curvature radius 9 km), in such a way that no direct view of the core is possible: this means no fast-neutron contamination and thus very low backgrounds levels. D23 has been designed to work with or without polarized neutrons, in the incident wavelength range 1 - 3 Å. D23 can support large sample environments (high field cryomagnets, pressure cells, dilution fridges, …) and is therefore devoted to the determination of magnetic structures, magnetic phase diagrams and magnetization density maps.

The primary protection is equipped with two different monochromators: a vertical focused PG 002 (in transmission) and a flat Cu 200 (in reflection). In the secondary shielding, a Heusler 111 (in transmission) can be mounted to provide polarized neutrons (double monochromator geometry, with PG as first monochromator). The diffractometer is constituted of a sample table (rotation of the sample : ω angle) and of a lifting detector that can rotate around the sample in the horizontal plane (γ angle) and move out of the horizontal plane (ν angle). All this device is mounted on air cushions, to change automatically the incoming neutron wavelength in the range 1 - 3 Å (unpolarized neutrons) and 1.2 - 2.4 Å (polarized neutrons).

• The diffractometer has the following characteristics:
  a fully non magnetic mechanics, to allow the use of high magnetic fields (12 and 15 T magnets);
• a compact diffractometer designed in a symmetric way, to allow diffraction to the right or to the left, with a maximum Bragg angle 2θB ≈ 130° on both sides;
• using a normal beam mode: the lifting detector is mounted in an arc, and can cover a symmetric angular range ν ≈ ± 30°. This is of particular importance to use all the split cryomagnets available at the ILL;
• the motors have been dimensioned to provide a 6°/s maximum speed for the different movements.

The standard cryogenic equipment available on the machine is: vertical field cryomagnets 6 and 12 T (with the possibility to use a dilution insert), and 15 T, horizontal field cryomagnet 4 T (with the possibility to use a dilution insert), ILL pressure cells (5 to 30 kbar), a 30 mK dilution and standard ILL orange cryostats.