Monte-Carlo modelling of the HRPD guide using distributed computing

Simulated diffraction on Hrpd

Simulated diffraction for cubic ZrW2O8 on Hrpd using the new guide. Only a small portion of the full range (which extends to 120,000μs) is shown.
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Whether designing a new neutron instrument or upgrading an existing one, Monte-Carlo (MC) simulations play an increasingly important role in optimising instrument performance.

The final design of the supermirror guide upgrade for the high-resolution powder diffractometer (HRPD) at ISIS, which will significantly enhance the neutron flux that is incident upon the sample, has been heavily influenced by MC simulations performed using the McStas computer program. Such simulations are computationally demanding and by distributing subcomponents of the calculation over a network of several hundred desktop personal computers, controlled by the GridMP system, simulations were able to be performed in much greater detail than ever before. In fact, not only could incident flux distributions be rapidly simulated as the design was altered, but entire diffraction patterns for wellcharacterised reference materials could also be rendered. The latter calculation for zirconium tungstate accrued some 230 days of CPU time in only 2.5 calendar days. Such calculations are clearly impractical for a single processor PC.

RM Ibberson, KS Knight, L Chapon, TAN Griffin and K Shankland (ISIS)

Research date: December 2007

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