Design and Implementation of a High Resolution DAQ System for an (e, 2e+ion) Electron Momentum Spectrometer

An (e, 2e+ion) Electron momentum spectrometer (EMS) upgraded from the third-generation (e, 2e) spectrometer is constructed in the University of Science and Technology of China (USTC). In the EMS, the energy-momentum density of electrons is derived through the charge measurement using the signals of the position sensitive detector (PSD). The information of ion fragments is derived through the time measurement and that information will be used for more research on collision dynamics. A PXI-based data acquisition (DAQ) system was designed. The system mainly consists of a 6-channel charge digital module (CDM) and a 9-channel time digital module (TDM). Shaping amplifiers (SAs) are also designed for charge measurement with CDM. According to the design specification, the CDM with SAs needs to measure charge from 100 to 900 fC with an accuracy of better than 1%. The TDM needs to measure the flight time from 0 to 15 us with a resolution of better than 100 ps. The TDM and CDM can be combined to run synchronously using a coincidence unit which also rejects the background events based on the tracking information of the electrons and the ions. Test results indicate that, within the dynamic range, the accuracy of the CDM is better than 0.4%. The RMS time resolution of better than 30 ps is achieved by using the method of time-to-digital converter (TDC) implemented in a field-programmable gate arrays (FPGA). The DAQ system has been assembled and works well with the EMS detectors.