Development of π and π/2 flippers for a neutron spin echo spectrometer

Abstract

For a time-of-flight neutron spin echo (TOF-NSE) spectrometer at a pulsed spallation neutron source, we previously designed new-type π and π/2 flippers which operate with steady current for a white neutron beam. The new-type spin flippers consist of a modified current sheet and Helmholtz coils. Performance tests of the new-type flippers with the modified current sheet made newly were carried out using ISSP-NSE at C2–2 port of JRR-3M in JAERI (Tokai). We replaced all of the Mezei-type π and π/2 flippers with the new-type ones and observed the NSE signal of neutrons scattered elastically from a stacked graphite sheet (grafoil). As the π flipper of iNSE (relocated ISSP–NSE), the new-type π flipper is installed and runs well. We also carried out performance tests of a tiny TOF-NSE machine with the new-type π and π/2 flippers using a pulsed white neutron beam at polarized neutron reflectometer of Neutron Science Laboratory, High Energy Accelerator Research Organization and we observed the TOF-NSE signal pattern, which gave direct evidence that the flippers worked for a pulsed white neutron beam. The new-type π and π/2 flipper operated well without tuning independently of the neutron wavelength. The operation is very easy, that is, one has to tune only the correction field from Helmholtz coils for a given precession field.