Simulation and implementation of multiplexing modes on cold-neutron triple-axis spectrometer SIKA

SIKA, a high-flux cold-neutron triple-axis spectrometer at the open-pool Australian lightwater reactor (OPAL) at the Australian Nuclear Science and Technology Organisation (ANSTO), is equipped with a 13-blade analyser and position-sensitive detector. This multiplexing design endows SIKA high flexibility to run in both traditional triple-axis and multiplexing analyser modes. In this study, two different multiplexing modes on SIKA are simulated using Monte Carlo ray-tracing methods. The simulation results demonstrate SIKA's capabilities to work in these operational modes, especially, the multi-Q const-E-f mode, where Q is the scattering wavevector and E-f is the final neutron energy. This capability was demonstrated by measuring the phonon dispersion of a Pb single-crystal sample with the multi-Q const-E-f mode on SIKA. Compared to the traditional and multi-analyser triple-axis spectrometers, multiplexing modes on SIKA combine the advantages of the high data-acquisition efficiency and flexibility to focus on local areas of interest in the momentum-energy transfer space, namely, the (Q, h omega) space.