Cost Optimisation of an Instrument Suite at an Accelerator-Driven Spallation Source

This artcile presents an optimisation of performance and cost of neutron scattering instrumentation at the European Spallation Source. This is done by trading detailed cost functions against beam transmission functions in a multi-dimensional, yet simple, parameter space. On the one hand, the neutron guide cost increases as a power of the desired beam divergence, and inversely with the minimum wavelength, due to the supermirror coating needed. On the other hand, the more neutrons are transported to the instrument the greater are the shielding costs to deal with the gamma rays that result from the eventual absorption of the neutrons. There are additional factors in that many of the parameters defining the neutron guide geometry are continuous variables, and the straightness of the guide increases the transmission of high energy spallation products, which affect the specifications of particularly heavy hardware, such as heavy shutters and additional shielding, beam stops etc. Over the suite of 16 instruments, a maximum potential cost saving is identified in the vicinity of 20 M\euro \,, with negligible penalties on instrument performance and bandwidth, by trading minimum neutron wavelength $\lambda$ against total optical costs and shielding costs. Finally, these cost calculations are shown to be consistent with those at real world, existing spallation source facilities.