Neutronic Developments on TOSCA and VESPA: Progress to Date

We report recent developments regarding the TOSCA (ISIS, UK) and VESPA (ESS, Sweden) neutron broadband chemical spectrometers, both joint ventures between CNR (IT) and ISIS (UK). TOSCA has seen the first major upgrade since it first became operational over fifteen years ago. The new design of the primary spectrometer, which exploits a state-of-the-art, high-m neutron guide and associated chopper system, is boosting the useful neutron flux by over an order of magnitude. Feasibility studies for an upgrade of the secondary spectrometer have been performed, outlining an additional order-of-magnitude gain in performance. In the case of VESPA, the novel characteristics and challenges arising from a long-pulse spallation source such as ESS are part of the drivers of the instrument design. For both the primary and secondary spectrometers, a detailed analysis of expected performance, supported by both simulations and analytical models, is being carried out, also capitalizing from experience on TOSCA. Indeed, for instrument design and optimization, extensive neutron-transport simulations and baseline studies of neutronic response have become a must, along with extensive benchmarking against much-needed experimental data. All these combined efforts represent the first opportunity to benchmark a broadband, high-resolution chemical spectrometer in terms of measured vs. simulated response.