Fast Monte Carlo simulation of a dispersive sample on the SEQUOIA spectrometer at the SNS

Abstract

Simulation of an inelastic scattering experiment, with a sample and a large pixilated detector, usually requires days of time because of finite processor speeds. We report simulations on an spallation neutron source (SNS) instrument, SEQUOIA, that reduce the time to less than 2 h by using parallelization and the resources of the TeraGrid. SEQUOIA is a fine resolution (ΔE/E_i ∼ 1%) chopper spectrometer under construction at the SNS. It utilizes incident energies from E_i = 20 meV–2 eV and will have ∼ 144,000 detector pixels covering 1.6 Sr of solid angle. The full spectrometer, including a 1-D dispersive sample, has been simulated using the Monte Carlo package McStas. This paper summarizes the method of parallelization for and results from these simulations. In addition, limitations of and proposed improvements to current analysis software will be discussed.