Design, assembly, and testing of the Tonne-Scale prototype of the DarkSide-20k detector for dark matter search with liquid Argon

Weakly Interacting Massive Particles (WIMPs) are among the leading candidates for dark matter (DM), potentially detectable via rare interactions with atomic nuclei. Direct detection relies on measuring the energy deposited when WIMPs scatter elastically off target atoms, producing nuclear recoils (NR). In liquid argon (LAr) detectors, these interactions generate scintillation light, which can be collected and analyzed to distinguish NRs from dominant electron recoils (ER) backgrounds using Pulse Shape Discrimination (PSD). The DarkSide program has pioneered the use of dual-phase LAr time projection chambers (LAr-TPCs) with ultra-pure underground argon (UAr). DarkSide-50, the first successful experiment in this program, demonstrated the feasibility of this approach with 50 kg of UAr, providing crucial proof-of-principle for large-scale detectors. Building on this success, DarkSide-20k, currently under construction at the Laboratori Nazionali del Gran Sasso (LNGS), Italy, will employ 100 tonnes of UAr and custom cryogenic Silicon Photomultiplier (SiPM) arrays to efficiently detect scintillation light within a novel acrylic-based TPC structure. To address the technical and engineering challenges of scaling up from DarkSide-50, a tonne-scale prototype detector was designed, commissioned, and operated at LNGS. This demonstrator faithfully reproduced the mechanical design and integrated critical subsystems of the full DarkSide-20k Inner Detector, enabling validation of cryogenic performance, high-voltage stability, material compatibility, structural integration, and assembly procedures under realistic operational conditions. The central focus of this thesis is on the prototyping work on this demonstrator, to which I contributed decisively through its successful completion.