Overview

On each HRS the detector system has two planes of trigger scintillators S1 and S2. The HA detector stack includes an optional third plane, S3. The mounting schemes of these planes are different. S1 is clamped to the detector frame through an additional Al channel, while S2 is assembled on a sub frame, which can slide on rails into the detector frame. S3 has strong a heavy sub frame, which can be mounted on the top of the HA detector frame. Figure  5.5 shows the mounting scheme for S1.

Figure 5.5: S1 mounting

1.

S1 and S2 each consist of six paddles. Each S1 paddle has an active area of 29.5 cm by 35.5 cm. Each S2 paddle has an active area of 54.0 cm by 37.0 cm. The counters are made of 5 mm thick BICRON 408 plastic scintillator and use multi-strip adiabatic light guides which end in a long cylindrical spool. There is an inlet for optical fiber mounted on the side of the cylindrical light guide. Each paddle is viewed by two 2" photo multiplier tubes (Burle 8575). The S1 paddles are installed at a small angle to the average plane and overlap by 10 mm. They are supported from PMT housings. The S2 paddles have only 5 mm overlap. Paddles are supported right outside the active area to minimize deflection of the plastic scintillator and the torque applied to the mounting of the PMT housing.