TOSCA Instrument Review
16 Dec 2014



TOSCA: Present and Future

​TOSCA. Gain vs. wavenumber at the sample position as a function of guide m-number

TOSCA has changed the area of neutron molecular spectroscopy, bringing in a vibrant chemistry-based user community to neutrons, as documented here. Following the 2013 instrument review carried by an international panel of experts, the panel stated that “The document we received as well as the presentation and the tour at the instrument site gave us an impressive overview on the capacities of this instrument that has kept a leading role in the field of inverted geometry spectrometers dedicated to chemical spectroscopy” as found in the final recommendations report.

The scientific output of TOSCA, accounting for 153 publications (in the 2008-2013 period), was rated as outstanding by the panel of experts based “both in terms of publications and also with respect to educational effort (20 theses since 2008), …, not to forget the impressive return of 0.8 papers/accepted experiment”.

Based on these attainments the IPE recommended that “TOSCA: The provision of a high m guide to enhance the flux available to the instrument”. Such a guide upgrade is required to enhance the flux available to the instrument and “has to be taken up with the highest priority”.

The proposed TOSCA upgrade is needed for it to become competitive with current generation instruments such as Vision at SNS and Lagrange at ILL. It will enable TOSCA to deal with more demanding experiments making possible the study of weakly scattering samples and non-hydrogenous materials which will take science at ISIS a step further.

Following these recommendations, intensive work is being carried out to implement the guide upgrade. Simulations to assess current performance and steer future upgrades concerning the best guide configuration and the most effective gain ratio have been conducted, which resulted in an MSc thesis and a paper. According to Figure 1, results show that installing a guide will result in a flux increase up to two-orders of magnitude (left image), without sacrificing the instrument resolution (right image).

Figure 1. Left image: Gain vs. wavenumber at the sample position as a function of guide m-number; Right image: Simulated spectra of ice at a temperature of 10 K using the inelastic backscattering bank at 135°. The legend indicates different guide configurations as described in the text

At present, the flux gain and the best guide configuration have been optimized in close collaboration with ISIS Engineering. As an outcome, a tender for the first guide section has been issued and quotes received. The upgraded TOSCA beamline is expected to be fully operational under the new configuration in 2016.