Trigger system changes for the HERMES III accelerator

This paper describes the hardware changes made to the triggering system of the HERMES III accelerator at Sandia National Laboratories, New Mexico. The HERMES III accelerator is a gamma ray simulator producing 100 kRad dose per shot with a full width half max pulse duration of approximately 25 nanoseconds and averaging six shots per day. For each accelerator test, approximately 400 probe signals are recorded over approximately 65 digitizers. The original digitizer trigger system employed numerous independent legacy signal generators resulting in non-referenceable digitizer time bases. We detail our efforts to reference the digitizer time bases together using a modular and scalable approach with commercial-off-the-shelf components. This upgraded trigger system presently measures a maximum digitizer trigger time spread of less than two nanoseconds across the 65+ digitizers. This document details the hardware changes, provides a summary of the accelerator charging process, presents “one-line” trigger system diagrams and summarizes the times of interest for a typical HERMES accelerator shot.