Characterization of the BIFROST spectrometer through virtual experiments

Abstract

Using the Monte Carlo ray tracing package McStas, we illustrate the possibilities of creating virtual experiments of the neutron spectrometer BIFROST at the European Spallation Source, ESS. With this model, we are able to benchmark BIFROST with respect to expected intensity, $Q$- and energy-resolution. The simulations reproduce the expected resolution behavior and quantify effects that are difficult to capture analytically, including a wavelength-dependent edge enhancement arising from a combination of the long-pulsed source and the pulse-shaping chopper. Furthermore, we present an antiferromagnetic (AF) spin wave simulation, which we use to create realistic datasets at different instrument operation settings. Our virtual experiments focus on realistic dispersive dynamics and illustrate how the virtual experiment approach reveal resolution effects, not easily calculable via analytical models. This demonstrates the crucial role of numerical simulations in the planning of challenging experiments.