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

摘要

VOR, the versatile optimal resolution chopper spectrometer, is designed toprobe dynamic phenomena that are currently inaccessible for inelastic neutronscattering due to flux limitations. VOR is a short instrument by the standardsof the European Spallation Source (ESS), 30.2 m moderator to sample, andprovides instantaneous access to a broad dynamic range, 1 - 120 meV within eachESS period. The short instrument length combined with the long ESS pulse widthenables a quadratic flux increase, even at longer wavelengths, by relaxingenergy resolution from $\Delta$E/E = 1% up to $\Delta$E/E = 7%. This isimpossible both on a long chopper spectrometer at the ESS and with instrumentsat short pulsed sources. In comparison to current day chopper spectrometers,VOR can offer an order of magnitude improvement in flux for equivalent energyresolutions, $\Delta$E/E = 1-3%. Further relaxing the energy resolution enablesVOR to gain an extra order of magnitude in flux. In addition, VOR has beenoptimised for repetition rate multiplication (RRM) and is therefore able tomeasure, in a single ESS period, 6 - 14 incident wavelengths, across awavelength band of 9 \AA{} with a novel chopper configuration that transmitsall incident wavelengths with equivalent counting statistics. Thecharacteristics of VOR make it a unique instrument with capabilities to accesssmall, limited-lifetime samples and transient phenomena with inelastic neutronscattering.