Abstract
The wide angular-range chopper spectrometer ARCS at the Spallation Neutron Source (SNS) is
optimized to provide a high neutron flux at the sample position with a large solid angle of
detector coverage. The instrument incorporates modern neutron instrumentation, such as an
elliptically-focused neutron guide, high speed magnetic bearing choppers and a massive array of
3He linear position sensitive detectors. Novel features of the spectrometer include the use of a
large gate valve between the sample and detector vacuum chambers and the placement of the
detectors within the vacuum, both of which provide a window-free final flight path to minimize
background scattering while allowing rapid changing of the sample and sample environment
equipment. ARCS views the SNS decoupled ambient temperature water moderator, using
neutrons with incident energy typically in the range from 15 to 1500 meV. This range, coupled
with the large detector coverage, allows a wide variety of studies of excitations in condensed
matter, such as lattice dynamics and magnetism, in both powder and single-crystal samples.
Comparisons of early results to both analytical and Monte Carlo simulation of the instrument
performance demonstrate that the instrument is operating as expected and its neutronic
performance is understood. ARCS is currently in the SNS user program, and continues to
improve its scientific productivity by incorporating new instrumentation to increase the range of
science covered and improve its effectiveness in data collection.
