The ATLAS Strip Detector System for the High-Luminosity LHC.

The ATLAS experiment at the Large Hadron Collider (LHC) is currently preparing for a major upgrade of the Inner Tracking for the Phase-II LHC operation (known as HL-LHC), scheduled to start in 2026. In order to achieve the integrated luminosity of 4000 fb${}^{-1}$, the instantaneous luminosity is expected to reach unprecedented values, resulting in about 200 proton-proton interactions in a typical bunch crossing. The particle densities and radiation levels will exceed current levels by a factor of ten. The radiation damage at the full integrated luminosity implies integrated hadron fluencies of more than $2\times10^{16} \text{n}_{\text{eq}}/\text{cm}^2$, requiring a complete replacement of the existing Inner Detector. An all-silicon Inner Tracker (ITk) is under development with a pixel detector surrounded by a strip detector, aiming to provide increased tracking coverage up to eta=4. In this contribution, we will give an overview of the strip detector system for this ATLAS upgrade. With the R&D phase and the system design completed, and prototyping in its final stages, we are now for the first time able to present the entire system as it will be built, with results available for the vast majority of system components. This will include detector modules which integrate 6” strip sensors, dedicated radiation hard ASICs and front-end read-out electronics mounted directly on the active side of the silicon strip sensors. We will also present the read-out, powering and control system that services and controls the modules and allows to transport the data collected from the modules to the central read-out and trigger electronics. For this submission, we will focus on the strip detector system as a whole, and highlight the results obtained with the production generation of ASICs and silicon strip sensors. In addition, we will show the expected performance of the strip system, based on recent test-beam results of un-irradiated and irradiated modules.