PSI - Issue 78

Michele Angiolilli et al. / Procedia Structural Integrity 78 (2026) 1807–1814

1811

into the gaseous argon phase. There, the electrons gain enough energy to excite the gas, leading to secondary electro luminescence (S2). Positioned just above and below the TPC are densely packed arrays of Silicon Photomultipliers (SiPMs), which detect visible light converted from the original VUV scintillation of argon by a wavelength shifter (i.e., Tetraphenyl butadiene - TPB). These optical planes detect both the prompt S1 light produced immediately after an interaction and the delayed S2 signal generated in the gas, allowing for three-dimensional event reconstruction and powerful discrimination between nuclear and electronic recoils. Surrounding the vessel, a thin plastic passive shielding layer – equipped with photodetectors – and a massive volume of liquid atmospheric argon AAr ( ∼ 600 tons) o ff er comprehensive protection against cosmic rays and radio genic backgrounds, ensuring the sensitivity needed to probe rare WIMP interactions. The cross-sectional view of the detector inside the cryostat and of the detector alone are shown in Fig. 1c-d. Before the detector can be operated, several temporary auxiliary engineering structures must be implemented to enable its safe, precise, and clean installation inside the cryostat. These include, most notably, the false floor system installed within the cryostat to support loads during the assembly of the detector, and the metallic framework designed to sustain a clean room above it. Although not part of the cryostat or the detector itself, these systems are critical to ensure the correct positioning, handling, and long-term operational conditions of the experiment. Their design is governed by stringent mechanical, geometrical, and procedural requirements, as they must accommodate specific assembly sequences, be compatible with subsequent dismantling operations, and ensure that the induced stresses remain safely below the design limits of the cryostat and associated components. The false floor was installed inside the cryostat in June 2025, directly resting on the primary corrugated membrane. It is specifically required to withstand the loads associated with the installation phases of the detector inside the cryostat, and will be fully removed once the assembly of the detector is complete and the top caps – which had been previously disassembled as described in §2.2 – are placed back in position, prior to filling the cryostat volume with LAr. All structural elements of the false floor have been designed to be dismantled and extracted through the cryostat manhole (with a nominal diameter of 700 mm), as no cutting operations are permitted during disassembly for cleanliness reasons. Consequently, predominantly bolted and clamped connections have been adopted, and any welded components have been dimensioned so that at least one side remains smaller than the manhole diameter, ensuring their removal. The system must be su ffi ciently sti ff to uniformly distribute loads, preventing local stresses that could lead to cracking of the membrane beneath. A SS upper covering was required for cleanliness reasons, but its thickness has been carefully limited to balance mechanical performance, cost considerations, and ease of handling during removal. Hence, the final design consists of a combined system made of a 5 mm thick AISI304 SS plate, grating elements (50 × 3 / 25 × 76), and S275 I-beams lattice beams (made of IPE100 cross-section), all clamped together to maximize structural e ffi ciency. Under the I-beam system a total of 238 steel feet with circular ribbed plates were defined. A maximum gap of approximately 1–2 mm between adjacent SS plates is maintained, with appropriate silicon sealing applied to accommodate potential movements and ensure airtightness. For this latter purpose, and also to limit vertical misalignments, an intermediate 5 mm thick HDPE layer has been added at the grating-to-SS plate interface. Finally, to prevent lateral impacts during accidental events, such as seismic actions, which could compromise or damage the delicate insulation system, dedicated lateral protection devices have been installed. These consist of HDPE elements with a thickness of 70 mm and a cross-section of 200 × 250 mm, combined with steel plates. A total of 16 such devices have been deployed, arranged as four units on each side of the cryostat. Details are illustrated in Fig.3 a. The clean room structure will be installed atop the DS-20k cryostat and will serve as the controlled environment area for assembling the DS-20k detector under low-contamination conditions, at least ISO7 particulate class. This structure must comply with stringent structural criteria to ensure that the stresses transmitted to the cryostat elements remain within the limits established in the final design documentation. Additionally, it must fulfill precise geometric constraints that allow for the passage and initial handling of large detector components using the existing 20 + 20-ton overhead crane system located in Hall C. The clean room itself is designed to support an internal 5-ton crane, as well as to accommodate a dedicated framework for mounting fan filter units (FFUs). Moreover, the entire supporting structure must be easily disassembled and reassembled in modular blocks to facilitate the various sequential installation phases required for the detector integration. These combined requirements make the clean room a critical auxiliary system, 4. Engineering Infrastructure for the Detector Installation