From IN3 to IN24: a design study

Abstract The three-axis spectrometer IN3 was one of the first instruments built up at the HFR ILL, Grenoble. The instrument is located at a thermal guide coated with natural Nickel. We have investigated the possible performance gain by utilisation of modern supermirror technique. Monte Carlo simulations with the program package McStas have been performed to calculate intensity gain factors and the changes in energy resolution. We propose to create a virtual source at the end of the guide. A large double focusing monochromator will allow to get monochromatic focusing conditions. A further focusing guide between monochromator and sample will increase the intensity gain up to a factor of 5–6 compared to the present IN3. Combined with a better energy resolution we argue a performance gain factor 8, upgrading “IN3 to IN24”.