Focus: Project of a Space and Time Focussing Time-of-Flight Spectrometer for Cold Neutrons at the Spallation Source SINQ of the Paul Scherrer Institute

Abstract

The physical design of FOCUS, a new time-of-flight (TOF) spectrometer for cold neutrons located at the continuous spallation source SINQ at the Paul Scherrer Institute/CH is presented. The main purpose of the instrument is to provide a versatile TOF machine being suited for a large variety of applications. The concept of the instrument consists in the combination of a doubly focussing monochromator with a Fermi-chopper. The monochromator will be provided with variable curvatures in both horizontal and vertical direction. By variable distances between the main spectrometer components FOCUS will have the option to be operated either in time focussing or monochromatic focussing mode for quasielastic and inelastic scattering applications, respectively. By means of two interchangeable monochromators a continuous wavelength band ranging from 2Å up to 18Å will be accessible. Monte Car10 simulations for an ideal Pb-target at SINQ show that for 4Å and 6Å and in its time focussing mode FOCUS will yield comparable energy resolutions in connection with 70–90% of the intensity of the time focussing TOF spectrometer IN6 at the ILL.