  The DIRC, a new type of Cherenkov imaging device, has been selected as the
primary particle identification system for the BABAR detector at the asymmetric
B-factory, PEP-II. It is based on total internal reflection and uses long,
rectangular bars made from synthetic fused silica as Cherenkov radiators and
light guides. In this paper, the principles of the DIRC ring imaging Cherenkov
technique are explained and results from the prototype program are presented.
The studies of the optical properties and radiation hardness of the quartz
radiators are described, followed by a discussion of the detector design.
