5.5.2.2 Overview

Next: 5.5.2.4 Handling Considerations Previous: Trigger Scintillators

5.5.2.2 Overview

Both HRS detector systems have two planes of trigger scintillators S1 and S2 following the Vertical Drift Chambers. In addition, the hadron HRS stack includes a thirs plane, S3. The S1 and S2 planes utilize 2" photomultiplier tubes while the S3 plane has 5" PMTs.

A schematic diagram of the 2" PMT Base is shown in figure . The Base consists of three main components. The Front Tubular Housing (06), which encloses the PMT, part of the scintillator counter's light guide (01), and the mu-metal shield (10). The actual base with the socket and dynode chain is a separate part, actually an assembly of parts (09-19). The Rear Tubular Housing (07) completes the assembly and encloses the dynode chain and wiring. The three main sections join at the coupling nut (14), which threads partly inside the front tubular housing, while the rear tubular housing threads on the remaining part.

The PMT and the electronic amplification components mounted on a P.C. board (15) are enclosed in an aluminum Faraday cage, which assures rigidity and protection from stray RF fields. The mu-metal shield is at cathode potential to minimize the dark current due to capacitance discharge in the photocathode glass window.

**Figure:** The 2" PMT base used in S1 and S2 trigger scintillators

Next: 5.5.2.4 Handling Considerations Previous: Trigger Scintillators

10/13/1997