Real-time data analysis using the WaveDREAM data acquisition system

The WaveDREAM data acquisition (DAQ) system, based on the DRS4 switched capacitor array waveform digitizing chip, provides Giga-samples per second (GSPS) digitization in a region of interest together with continuous sampling of the input signals at 120 Mega-samples per second (MSPS). In the Field-programmable gate array (FPGA), the 120 MSPS signal can be used to build arbitrarily complex trigger logic and to perform real-time data analysis with hard real-time constraints in the microseconds range. As an application example, the system is configured and optimized for the readout of an array of high-pressure 4He fast neutron detectors. At each end of the detector, photomultiplier tubes (PMTs) collect and amplify the light. Variable gain amplifiers (VGAs) scale the PMT signals such that they optimally fit into the dynamic range of the DRS4 integrated circuit (IC). The trigger in the FPGA employs a coincidence logic between the two PMT signals of a detector to effectively filter out PMT dark counts. Real-time data analysis includes energy deposit measurements and a pulse shape discrimination (PSD) algorithm to reject events originated by gamma radiation, thus greatly reducing the data rate to be processed offline. The high-resolution GSPS signal from the DRS4 IC is used to obtain precise event timing information, thereby enabling neutron time of flight (ToF) measurements with nanosecond time precision. In addition, this signal can be used during offline data processing to strengthen the analysis results. Thus, the WaveDREAM DAQ provides both efficiency (real-time data analysis) and precision (GSPS signal for offline analysis) at low cost.