Time-of-flight diffraction with multiple frame overlap Part II: The strain scanner POLDI at PSI

Abstract POLDI (Pulse-OverLap DIffractometer) is a multiple pulse-overlap diffractometer at PSI, which is designed mainly for strain-scanning experiments. The multiple pulse-overlap method made it possible to build a time-of-flight diffractometer at a continuous neutron source with short flight path, high resolution and high intensity. The best achievable resolutions for the relative linewidths of the Bragg reflections are between 1×10 −3 and 2×10 −3 , depending on the lattice spacing. The layout of the instrument and the features of the chopper, the neutron mirror and the 3 He detector in time-focusing geometry are presented. The overall performance of the instrument is discussed with examples of strain-field measurements.