Development of a large-area curved Trench-MWPC ³He detector for the D16 neutron diffractometer at the ILL

The D16 instrument is a versatile cold-neutron diffractometer at the ILL. It has benefited from a number of upgrades over the years, such as the installation of a large-area 3 He Multi-Wire Proportional Chamber (MWPC) in 2011. This detector has provided a resolution of 1 mm x 1 mm over an area of 32 cm x 32 cm. After 12 years of operation, it was replaced by a new curved detector which covers a wider solid angle while maintaining a high angular resolution. Its 86° horizontal angular coverage makes it possible to perform time-resolved experiments with a large q-range. This new detector is based on the Trench-MWPC detector technology developed at the ILL. In the D16 Trench-MWPC, 6 modules are mounted side by side in an 3 He-filled curved vessel. Each module consists of 192 cathode blades positioned every 2 mm, and 192 anode wires spaced by 1.5 mm. The radius of curvature of the cathode blades is 1150 mm, providing a parallax-free resolution of 0.075°, horizontally along the 86° angular coverage of the 38 cm high detector. The various steps of the fabrication and mechanical inspection of the D16 Trench-MWPC detector modules and pressure vessel are presented, as well as experimental results obtained during the characterisation of the detector with neutrons.