The Bates Large Acceptance Spectrometer Toroid (BLAST) is a
detector designed to study in a comprehensive and precise way the
spin-dependent electromagnetic response in one and few-body systems over a
large kinematic range using the MIT-Bates South Hall Ring. Currently it is
used to measure spin-dependent scattering from the elastic to the nucleon
resonance region for hydrogen and deuterium using the Bates longitudinally
polarized electron beam at beam energies up to 850 MeV and polarized
internal gas targets of hydrogen and deuterium. The BLAST detector
consists of an eight-sector copper coil array producing a toroidal
magnetic field, instrumented with two opposing wedge-shaped sectors of
wire-chambers, scintillation detectors, Cherenkov counters and neutron
detectors. The BLAST Cherenkov counters are used for particle
identification.
Their index of refraction is good enough to discriminate against pions up
to at least 700 MeV/c. We report on the BLAST Cherenkov counters, their
design, construction and performance.