Fine-Resolution Fermi Chopper Spectrometer (SEQUOIA)
SEQUOIA is a direct geometry time-of-flight chopper spectrometer with fine energy transfer (ω) and wave-vector (Q) resolution. The instrument is being used to conduct forefront research on dynamical processes in materials. In particular, SEQUOIA is enabling unprecedented high-resolution inelastic neutron scattering studies of magnetic excitations and fluctuations and lattice vibrations.
The impact on condensed matter and materials science will span a wide cross-section of important research areas. Today these include strongly correlated electrons systems; high-temperature superconductors; colossal magnetoresistive materials; quantum and molecular magnetism; itinerant magnets and multilayers; alloys; ferroelectric, piezoelectric, and thermoelectric materials; and soft condensed matter.
SEQUOIA is also an outstanding tool for the investigation of novel systems and materials that are currently unknown and is a necessary complement to the other main SNS chopper spectrometer, ARCS. In general, SEQUOIA is the instrument of choice for experiments that require high Q and ω resolution and large solid angle at low-to-intermediate scattering angles.
To meet the technical requirements of fine resolution in both ω and Q, a 5.5 m flight path from the sample to detector bank is required. This detector bank covers scattering angles from -30 to 60° in the horizontal and ± 30° in the vertical in increments of ≈0.3°. Therefore the total solid angle coverage is 1.61 steradians. To optimize the flux on sample in this high-resolution configuration, the moderator-to-sample distance is as short as possible, that is, 20 m. The instrument can use the full source spectrum provided by the decoupled water moderator. Therefore it can be used to study excitations on energy scales ranging from a few millielectron volts up to a couple of electron volts. A supermirror neutron guide is included on the instrument to further enhance the flux of thermal neutrons on the sample.
An instrument development team (IDT) was assembled in support of SEQUOIA and consists primarily of representative scientists from ORNL Neutron Sciences and the Canadian Institute for Neutron Scattering. In addition, a group of distinguished scientists from the American neutron scattering community is represented.
