The Operational Experience, Challenges and Performance of the ATLAS Semiconductor Tracker during LHC Run-2

The Large Hadron Collider (LHC) completed its Run-2 operation period from 2015 through 2018, which delivered an integrated luminosity of 156~fb$^{-1}$ at a centre-of-mass $pp$ collision energy of 13~TeV. This marked ten years of successful operation of the ATLAS Semiconductor Tracker (SCT), which operated during Run 2 with instantaneous luminosity and pileup conditions that were far in excess of what the SCT was originally designed to meet. Nevertheless, thanks to various improvements on its operation, the SCT achieved high performance with a hit efficiency greater than 99\%. The effects of radiation damage, in particular significant increase of the leakage current and full depletion voltage, were observed during Run 2. Although those may risk the SCT operation in the Run-3 operation period starting in 2021, studies reveal that a sufficient margin of the SCT specification remains, which will ensure the safe operation until 2023.