A High Speed Trigger System for Total Deposited Energy Measurement in a Liquid Argon Calorimeter

A system to produce trigger signals measuring the total energy deposited in the liquid argon/lead shower counters of the SPEAR Mark II Detector at the Stanford Linear Accelerator Center is described. The trigger signals are developed by summing, filtering, and discriminating the signals from several thousand preamplifiers connected to the liquid argon detector strips. The system requirement of trigger information 430 ns after a particle has entered the shower counter led to a special filter design in which a leading edge sampling technique was utilized. A filtered signal representing the total deposited energy is measured by a fast level discriminator that is strobed in synchronization with the e+e- beam crossings of the SPEAR storage ring. This sampling of the filtered waveform produces a digital output that is delivered to the trigger logic.