A 250 MHz Level I Trigger and Distribution System for the GlueX Experiment

The GlueX detector now under construction at Jefferson Lab will search for exotic mesons though photoproduction (10 boolean AND 8 tagged photons per second) on a liquid hydrogen target. A Level I hardware trigger design is being developed to reduce total electromagnetic (> 200 MHz) and hadronic ( > 350 kHz) rates to less than 200 kHz. This trigger is deadtimeless and operates on a global synchronized 250 MHz clock. The core of the trigger design is based on a custom pipelined flash ADC board that uses a VXS backplane to collect samples from all ADCs in a VME crate. A custom switch-slot board called a Crate Trigger Processor (CTP) processes this data and passes the crate level data via a multi-lane fiber optic link to the Global Trigger Processing Crate (also VXS). Within this crate detector sub-system processor (SSP) boards can accept all individual crate links. The subsystem data are processed and finally passed to global trigger boards (GTP) where the final L1 decision is made. We present details of the trigger design and report some performance results on current prototype systems