An optical timing verification system for Alcator C-Mod

We have built a system to generate and optically distribute a TTL timing waveform around the experiment cell. This waveform provides recognizable time markers which when digitized allow time-bases of the data acquisition equipment and software to be independently verified. The system can be used off line to characterize repeatable system behavior, or channels can be dedicated to digitizing this reference waveform for every shot providing a check for triggering behavior, clock and trigger timing accuracy and overall system correctness. ing transient phenomena with different diagnostics at different locations is becoming increasingly important. As measuring frequencies increase it becomes more and more difficult to line up the samples of separate measurements in time. At the same time the channel count for many diagnostics is increasing, lowering the incremental cost of dedicating a channel for time-base verification. In this paper we will describe the system and its motivation, and provide initial results from its deployment.