  Ultra-cold neutrons (UCN), neutrons with energies low enough to be confined
by the Fermi potential in material bottles, are playing an increasing role in
measurements of fundamental properties of the neutron. The ability to
manipulate UCN with material guides and bottles, magnetic fields, and gravity
can lead to experiments with lower systematic errors than have been obtained in
experiments with cold neutron beams. The UCN densities provided by existing
reactor sources limit these experiments. The promise of much higher densities
from solid deuterium sources has led to proposed facilities coupled to both
reactor and spallation neutron sources. In this paper we report on the
performance of a prototype spallation neutron-driven solid deuterium source.
This source produced bottled UCN densities of 145 +/-7 UCN/cm3, about three
times greater than the largest bottled UCN densities previously reported. These
results indicate that a production UCN source with substantially higher
densities should be possible.
