  The trend in neutron sciences is toward integrating compact, high-brightness
moderators into new or upgraded facilities. Transporting neutrons from the
source to the sample position with a phase-space distribution tailored to
specific requirements is crucial to leverage high source brilliance. We have
investigated four guide concepts using Monte Carlo ray tracing simulations:
Montel beamline with nested Kirkpatrick-Baez mirrors, curved-tapered beamline
with a bender and straight sections, straight-elliptical beamline, and
curved-elliptical beamline. The straight-elliptical (curved-elliptical)
beamline features two half-ellipse guides connected by a straight
(non-straight) guide section. The neutron transport efficiency and phase space
homogeneity have been quantitatively compared. Our results show that the
straight-elliptical beamline performs best because of few neutron bounces on
the guide surface with small reflection angles, minimizing flux loss. The
Montel beamline provides the best spatial confinement of neutrons within the
desired region; however, there is a high thermal-neutron loss due to large
reflection angles. The curved-tapered beamline suffers from significant flux
loss due to high bounces, and it shows a non-uniform angular distribution
related to broad ranges of bounces and reflection angles. The non-straight
guide section of the curved-elliptical beamline increases phase space
inhomogeneity, leading to a spatially non-uniform beam profile. The results
apply to general neutron instruments that require transporting thermal and cold
neutrons from a compact, high-brilliance moderator to the sample location with
a moderate phase-space volume.
