The CLAS Cerenkov Detector

Construction

As part of CLAS, the Cerenkov detector is composed of six nominally identical ``sectors''. Each sector covers the angular region from approximately 8-45 degrees in theta, with the full CLAS coverage in phi. The mechanical construction of each sector consists of two sidewalls, which sit in the planes of the CLAS magnet coils, a "snout" piece at the vertex near the beamline, and a "45-degree wall" made of GreySeal, a composite material that is both strong and light.

There are three different types of mirrors in the Cerenkov detector: elliptical, hyperbolic, and cylindrical (in the order in which the Cerenkov light hits them). The elliptical and hyperbolic mirrors were constructed at RPI by a small army of undergraduate students under the supervision of an engineer. They were made by vacuum-sealing three layers of Kevlar around a foam core with epoxy, and then laminating a piece of aluminized Lexan onto the finished core. The Lexan was treated with magnesium fluoride to prevent oxidation of the aluminum.