  This paper describes the design and performance of a 50 liter, two-segment
$^{6}$Li-loaded liquid scintillator detector that was designed and operated as
prototype for the PROSPECT (Precision Reactor Oscillation and Spectrum)
Experiment. The two-segment detector was constructed according to the design
specifications of the experiment. It features low-mass optical separators, an
integrated source and optical calibration system, and materials that are
compatible with the $^{6}$Li-doped scintillator developed by PROSPECT. We
demonstrate a high light collection of 850$\pm$20 PE/MeV, an energy resolution
of $\sigma$ = 4.0$\pm$0.2% at 1 MeV, and efficient pulse-shape discrimination
of low $dE/dx$ (electronic recoil) and high $dE/dx$ (nuclear recoil) energy
depositions. An effective scintillation attenuation length of 85$\pm$3 cm is
measured in each segment. The 0.1% by mass concentration of $^{6}$Li in the
scintillator results in a measured neutron capture time of $\tau$ =
42.8$\pm$0.2 $\mu s$. The long-term stability of the scintillator is also
discussed. The detector response meets the criteria necessary for achieving the
PROSPECT physics goals and demonstrates features that may find application in
fast neutron detection.
