SUB-SAMPLE TIME-BASE RESOLUTION IN A HETEROGENEOUS DISTRIBUTED DATA ACQUISITION ENVIRONMENT

We have developed a reference timing system to verify and correct the time-bases for acquired time series data. This system allows for sub-sample time registration of data acquired from separate diagnostics using heterogeneous data acquisition hardware. The system was designed to recognize and repair several types of timing discrepancies including trigger recognition and configuration differences, clock rate slew, and data acquisition errors such as lost or mislabeled samples. When used as a dedicated time-reference standard, the system relaxes the requirements for cross-diagnostic data acquisition synchronization; time-bases can be unambiguously resolved from hardware that uses asynchronous clocks and triggers. This paper describes an automated system for generating sub-sample accurate time-bases across multiple diagnostic systems on the Alcator C-Mod device, a magnetic-confinement fusion experiment. The system has been demonstrated to accurately determine the times of measured phenomena in order to track point of origin and propagation around the experiment. In addition, timing errors in signals can be easily flagged and corrected. The initial installation has been applied to a variety of diagnostics, including fast, optically-based fluctuation diagnostics and plasma-sampling probes. These diagnostics are physically distributed around the experiment cell, have disparate digitization rates (0.1 MHz to 10 MHz) and operate with both synchronous and asynchronous clocks and triggers.