Design and Development of the Back-End Electronics for the IXPE Mission

The Imaging X-Ray Polarimetry Explorer IXPE mission will perform polarization measures of 2–8 keV X-rays. Imaging, spectroscopy, and timing will complement this measurement for a comprehensive study of soft X-rays. The launch of the IXPE NASA small explorer mission to a low earth orbit is due late 2021. We designed a subsystem of the scientific payload, which has three identical telescopes based on the detector unit. The Gas Pixel Detector and its back-end electronics are the core of these units, performing data acquisition and processing, event sequencing, and on-line data compression. The back-end electronics processes the auto-triggered output of the detector of 300 photons per second with 30% of dead-time. A radiation-tolerant FPGA implements the electronics custom algorithms, including two digital serial interfaces with a central on-board computer. One interface is used for command and control of the unit, while the other for scientific data transmission. We also designed comprehensive test equipment to emulate the on-board computer and to operate the electronics. This equipment uses an FPGA on a VMEbus board as the electrical interface for the electronics, transferring data to a personal computer with dedicated software infrastructure. In this paper, we shall discuss the design process of the back-end electronics and the results of laboratory tests and measurements with X-ray sources.