Wide Angular-Range Chopper Spectrometer

ARCS | BL-18 | SNS

Mission Statement

Illuminating excitations in condensed matter systems to enhance the fundamental understanding of dynamic processes in materials.

Instrument Description

ARCS is optimized to provide a high neutron flux at the sample and a large solid angle of detector coverage. The spectrometer is capable of selecting incident energies from a wide range, making it useful for studies of excitations from a few to several hundred milli-electron volts. An elliptically shaped supermirror guide in the incident flight path boosts the performance at the lower end of this range. The sample and detector vacuum chambers provide a window-free final flight path and incorporate a large gate valve to allow rapid sample changeout. A T0 neutron chopper not only blocks the prompt radiation from the source but also eliminates unwanted neutrons from the incident beam line. An oscillating radial collimator can reduce the background from complex sample environment equipment.

Applications

The increased sensitivity of ARCS offers new opportunities for scientific studies in:

Lattice Dynamics

Entropy and the effects of vibrational modes on stability and phase transitions of solids
Excitations in disordered materials; effects of nanoscale features on vibrational entropy and thermodynamic stability
Equations-of-state from the measured phonon density-of-states versus temperature and pressure
Phonons in correlated-electron materials; coupling of lattice and electronic degrees of freedom in high Tc, heavy-fermion and mixed valence materials

Magnetic Dynamics

High-temperature superconductivity-spin dynamics in superconductors and precursor compounds and crystal field spectroscopy
Low-dimensional systems; one-dimensional quantum magnets and low-dimensional conductors
Magnetism in actinide materials; heavy fermion magnetism and superconductivity

Chemical Physics

Deep inelastic neutron scattering studies of hydrogen and helium

Inelastic neutron scattering studies such as those conducted at ARCS can impact the development of important practical materials, such as ferroelectrics used in ultrasounds and thermoelectrics used to harvest energy from waste heat.

Specifications

Moderator	decoupled ambient water
Source – Fermi chopper distance	11.6 m
Chopper – sample distance	2.0 m
Sample – detector distance	3.0 m – 3.4 m cylindrical geometry
Incident energy range	10 – 1500 meV
Resolution (elastic)	3 – 5% E_i
Detector coverage horizontal	-28° – 135°
Detector coverage vertical	-27° – 26°
Minimum detector angle	3°
Beam Size	5 cm x 5 cm, with fully adjustable motorized slits in the horizontal and vertical directions