We describe an apparatus used to measure the triple-correlation term (\D
\hat{\sigma}_n\cdot p_e\times p_\nu) in the beta-decay of polarized neutrons.
The \D-coefficient is sensitive to possible violations of time reversal
invariance. The detector has an octagonal symmetry that optimizes
electron-proton coincidence rates and reduces systematic effects. A beam of
longitudinally polarized cold neutrons passes through the detector chamber,
where a small fraction beta-decay. The final-state protons are accelerated and
focused onto arrays of cooled semiconductor diodes, while the coincident
electrons are detected using panels of plastic scintillator. Details regarding
the design and performance of the proton detectors, beta detectors and the
electronics used in the data collection system are presented. The neutron beam
characteristics, the spin-transport magnetic fields, and polarization
measurements are also described.Comment: 15 pages, 13 figure
