System testing for the ITk pixel detector

In order to operate in the harsh radiation conditions of the High-Luminosity Large Hadron Collider (HL-LHC), the ATLAS experiment at CERN will undergo a number of upgrades over the LHC Long Shutdown 3 (2026-2030). Notably, the ATLAS Inner Detector will be completely replaced with an all-silicon Inner Tracker (ITk),  designed to cope with increased occupancy, bandwidth, and radiation damage. The ITk is comprised of a hybrid silicon pixel detector at its heart, surrounded by a silicon strip detector.

The ITk Pixel system will cover an active area of approximately 13 m², will have around 5 billion readout channels, and will use innovative concepts such as serial powering and CO2 cooling to an unprecedented scale. The design and prototyping period for the ITk Pixel detector is now complete, with many detector components already in the production or pre-production phase. System-level tests play a crucial role in the ITk Pixel testing programme, allowing validation of the interfaces between different detector components, and preparation for detector commissioning and operation. An overview of recent system-test efforts will be presented, including the recent operation of a 14-module serial powering chain at CERN.