Performance of the multidetector NSE spectrometer SPAN at BENSC

The neutron spin-echo spectroscopy (NSE) precession field, which is created by three pairs of coils with diameters 1, 3 and 4.8 m, respectively, is the peculiarity in the design of SPAN. Each pair is mounted in a Helmholtz-like fashion, with the electric currents oriented oppositely to each other, one coil above and one coil below the horizontal scattering plane. The centers of all coils are placed on the same vertical axis, which crosses the sample position. The NSE field is horizontal with axial symmetry. Particular care has been taken to shape the magnetic field around the sample, which is weak, vertical and very homogeneous. We present a first series of NSE measurements, which show that only little field adjustment is required to satisfy the exact echo condition (phase) simultaneously for a range of scattering angles and confirm the high axial symmetry of the precession field. The results show that the new magnetic field configuration of SPAN allows for multidetector NSE over a wide angular range.