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The Large Hadron Collider (LHC) is a proton-proton collider located at CERN in Geneva. It served in numerous scientific breakthroughs, including the discovery of the Higgs boson in 2012. In 2013, the LHC upgrade program was announced, aiming to deliver very high luminosity, a factor of 5 higher than the original design. This is known as the High-Luminosity LHC phase (HL-LHC). The aim is to achieve a luminosity of at least 5.10^34 cm-2s-1 and potentially 7.10^34 cm-2s-1. In this scenario, the average number of collisions per beam crossing would be 200 (compared with 50 in 2023, for example). The collider would then deliver an integrated luminosity of 4000 fb-1 in 12 years. The aim of such technical upgrades is of course to increase the measurement potential of the experiments, such as the increase of Higgs boson production or study the electroweak symmetry breaking, but also to explore physics beyond the Standard Model with, for example, supersymmetry. To cope with the increased data rate and higher radiation levels, the LHC detectors will also be upgraded. Among them, the ATLAS detector (A Toroidal LHC ApparatuS) which is undergoing a major upgrade: faster electronics on certain sub-systems, complete replacement of certain sub-detectors (for example, the new tracking detector ITk) or the addition of new ones such as High-Granularity Timing Detector (HGTD). HGTD will be installed in both endcaps of the ATLAS detector for HL-LHC in 2029. It will provide a precise measurement of the tracks’ times complementing the spatial information provided by ITk. This will greatly reduce the tracking ambiguities. Indeed, the high luminosity will bring a lot of simultaneous interactions between partons during proton bunch crossing, and it's important to distinguish between events that are interesting to study and the "pile up” ones. HGTD must be highly resistant to radiation since the estimated fluence will reach around 5.6 x 10^15 neq cm-2. The detector is based on LGAD semiconductor sensors, which are highly resistant to radiation and provide a time resolution of between 30 and 50 ps. The thesis work covers many aspects of HGTD design and operation and is organised as follows. Chapters 1 and 2 describe the ATLAS detector, the LHC, the HL-LHC phase and the future HGTD. Chapter 3 is dedicated to the mechanical R&D for the detector assembly procedure and the design of the support structures for modules. It is important that these supports are optimized for easy installation and replacement while maximizing the active sensitive area. It also covers the work on the HGTD heater demonstrator. Chapter 4 is dedicated to the analysis of data taken during test beams for the LGAD sensors performance studies. The aim is to select the LGAD specifications and the vendors that will produce them, based on their radiation hardness, detection efficiency and time resolution. Chapter 5 focuses on the performance of HGTD track reconstruction capabilities. A new method for improving the purity of efficiency is presented. Chapter 6 describes the integration of HGTD in a novel tracking software ACTS that will be used by the ATLAS experiment during the HL-LHC phase.