Technical Design Report for the Phase-II Upgrade of the ATLAS Tile Calorimeter

This Technical Design Report describes the project to upgrade the ATLAS Tile Calorimeter for the operation at the High Luminosity LHC. The High Luminosity LHC is planned to begin operation in 2026 and to deliver more than ten times the integrated luminosity (up to 4000 fb$^{-1}$ of the LHC Runs 1-3 combined. To achieve this integrated luminosity in a reasonable amount of time, an instantaneous luminosity of up to $7.5\times 10^{34}$ cm$^{-2}$s$^{-1}$ is required, corresponding to up to 200 simultaneous pp interactions per bunch crossing. The large luminosity offers the opportunity for a wealth of physics measurements but presents significant challenges to the detector as well as to the trigger and data acquisition systems in the form of increased trigger rates and detector occupancy. This document summarises the requirements and motivations for the Tile Calorimeter upgrade and gives a detailed technical description of the different components. It describes the beam tests with the prototypes in recent years and the plans for the assembly, quality assurance and the integration of the final system. The document also presents the key aspects of project management with an overview of the organisation, the schedule and the cost.