Monitoring single event upsets in SRAM-based FPGAs at the SuperKEKB interaction point

Abstract

In February 2016, the SuperKEKB positron-electron high-luminosity collider of the KEK laboratory (Tsukuba, Japan) started being commissioned. A dedicated commissioning detector, named BEAST2, has been used to characterize beam backgrounds before the Belle2 detector was rolled into the beams and to provide tuning parameters for Monte Carlo simulations. BEAST2 consists of a fiberglass support structure and several sub-detectors mounted onto it, including time projection chambers (TPCs) and He-3 tubes. In this work, we present direct measurements of radiation-induced single event upsets in a SRAM-based FPGA device installed in BEAST2 at a distance of ∼ 1 m from the beam interaction point. Our goal was to provide experimental results of the expected radiation-induced configuration upset rate and power consumption variation at Belle2 and at other experiments operating in similar radiation environments. Beam currents for both electron and positron rings spanned a range between 50 and 500 mA, therefore providing data about the FPGA operation in different radiation conditions. Even if the machine has not been providing collisions yet, as the beams were not focused to the interaction point, our results show a rate of 0.15 upsets/day averaged over the whole commissioning time frame. We had neither evidence of total dose effects on the FPGA power consumption nor of permanent damage to the device.