IN1-Lagrange will be a universal instrument oriented to studies of lattice and molecular excitations in complex materials in the form of phonon density of states (PDOS). Unique at ILL by the combination of high energy range and unrestricted temperature interval for samples. Unique in the world by the combination of high resolution and high count rate flexible resolution variation in a broad range the highest sensitivity.

IN1-Lagrange is a new configuration which will enhance and replace the present IN1-BeF configuration used for high energy neutron spectrometry. The goal is to meet the ever increasing demand in well-resolved vibration spectra from small amounts of new materials.
Neutrons which are inelastically scattered by the sample are filtered by a beryllium filter, then selected and redirected towards a neutron counter by an analyzer. The innovation comes from the cylindrical symmetry and from the elliptical shape of the analyzer. As the sample and counter are placed at the foci positions, sample and counter are the optical image from each other.
With this project, we expect to increase the count rate by a factor of 5, to lower the background by a factor of 10 and to improve the resolution by a factor of 4.

To reach the expected performances, an optimization of the filter thickness is needed. Calculations are performed to benchmark the models with the neutron measurements made on a beryllium sample and then extrapolate the results for the cylindrical filter which will be integrated on IN1.