A design study of VOR: a versatile optimal resolution chopper spectrometer for the ESS

TL;DR

VOR is a compact, versatile neutron spectrometer at ESS that offers high flux, broad energy range, and simultaneous multi-wavelength measurements, enabling new insights into dynamic phenomena in materials.

Contribution

The paper introduces VOR, a novel short chopper spectrometer design that significantly improves flux and energy resolution flexibility compared to existing instruments at ESS.

Findings

VOR achieves an order of magnitude higher flux at similar resolutions.

It can measure 6-14 incident wavelengths simultaneously.

VOR enables studies of small or transient samples previously inaccessible.

Abstract

VOR, the versatile optimal resolution chopper spectrometer, is designed to probe dynamic phenomena that are currently inaccessible for inelastic neutron scattering due to flux limitations. VOR is a short instrument by the standards of the European Spallation Source (ESS), 30.2 m moderator to sample, and provides instantaneous access to a broad dynamic range, 1 - 120 meV within each ESS period. The short instrument length combined with the long ESS pulse width enables a quadratic flux increase, even at longer wavelengths, by relaxing energy resolution from $\Delta$E/E = 1% up to $\Delta$E/E = 7%. This is impossible both on a long chopper spectrometer at the ESS and with instruments at short pulsed sources. In comparison to current day chopper spectrometers, VOR can offer an order of magnitude improvement in flux for equivalent energy resolutions, $\Delta$E/E = 1-3%. Further relaxing the energy resolution enables VOR to gain an extra order of magnitude in flux. In addition, VOR has been optimised for repetition rate multiplication (RRM) and is therefore able to measure, in a single ESS period, 6 - 14 incident wavelengths, across a wavelength band of 9 \AA{} with a novel chopper configuration that transmits all incident wavelengths with equivalent counting statistics. The characteristics of VOR make it a unique instrument with capabilities to access small, limited-lifetime samples and transient phenomena with inelastic neutron scattering.