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.

Keywords:

• Monte Carlo simulation
• Neutron Spectroscopy
• Neutron Instrumentation
• Parallel Computing

Acknowledgements

We wish to acknowledge the mechanical design work on SEQUOIA provided by D. Vandergriff and E. Hardin. We are grateful for stimulating discussions with M. Lumsden, T. Kelley, P. Peterson, S. Nagler, and S. Miller on data analysis issues. Computations were performed on TeraGrid at Oak Ridge under DAC allocation DMR060001. Oak Ridge TeraGrid efforts sponsored by the US National Science Foundation under interagency agreement DOE No. 0700-S664-A1, NSF Cooperative Agreement ACI-0352164 and Cooperative support agreement No. ACI-0338605. This work was performed at Oak Ridge National Laboratory, managed for the US D.O.E. by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725.