Guide design study for the high-resolution backscattering spectrometer FIRES

Different options are considered to transport cold neutrons along 90 m for the proposed new spectrometer FIRES at the ISIS facility. Monte Carlo simulations using the McStas programme package are used to assess the performance of various guide designs from the biological shield to the sample position. By employing a curved geometry, to avoid the direct line of sight, a hybrid design which combines a curved ballistic guide and an elliptic focusing section appears to be the best solution.