Members of the High Energy Cosmic Particles Focus Group, based at Jodrell Bank Observatory and Karlsruhe Institute of Technology, have constructed a benchtop prototype of a particle-detector system for the SKA. This system is a vital component for a Custom Experiment to use SKA-low to study particle cascades created by high-energy cosmic rays interacting in the atmosphere above the telescope. The purpose of this development work is to ensure that the final system is an efficient particle detector and does not emit any radio-frequency interference.
The benchtop prototype (pictured) has been used for a range of tests thus far, including a complete integrated test of the analogue signal path, using RF-over-fibre links developed for the SKA. A power-conditioning circuit board has been constructed and tested, and found to provide >60 dB suppression of any interference that might leak out of the detector along the power line. A key aspect of the system is the use of low-voltage silicon photomultipliers (SiPMs), which avoid the potential for radio interference from traditional photon detection with high-voltage photomultiplier tubes. After comparing four different models of SiPM, the development team has selected the SensL J-series for the final version. Tests with the J-series SiPMs have shown them to have timing precision better than 0.5 ns in this system, allowing them to localise high-energy particles passing through the prototype (see picture).