PSI - Issue 78

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

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Fig. 2. a) Final assembly stages of the top caps; b) Insulation Cross-section view; c) Detector hanging on the cryostat roof along with installed feedthroughs for support and signal extraction; d) Inner Detector hosted in the SS vessel.

with the assembly of a top cap a module taking place after the insulation system at the bottom and along the lateral walls had been completed. Finally, Fig. 2.b depicts a cross-sectional view of the insulation, highlighting the details of each layer. It should be noted that four of the five top caps, after an initial installation phase to verify alignment tolerances, were subsequently dismounted to allow for the installation of the inner detector.

3. Overview of the Detector components

The DS-20k experiment employs a dual-phase LAr-TPC, housed within a low-radioactivity SS vessel engineered to endure cryogenic temperatures, internal pressures, seismic loads, and long-term operation. Suspended inside the cryo stat by a support system that minimizes heat transfer and ensures precise alignment during thermal contraction, the vessel contains the active volume of underground-sourced LAr, continuously purified to achieve exceptional radiop urity. (see a recent work on computational fluid dynamics simulations and heat transfer calculations F. Acerbi et al. (2025)). The detector active volume is defined by thick, transparent PMMA (PolyMethyl MethAcrylate, i.e. acrylic) panels joined to form a barrel with an octagonal cross-section. These panels not only maintain structural integrity, but also contribute to neutron capture, enhancing background discrimination through an integrated veto system; (see R&D project in F. Acerbi et al. (2024)). When a WIMP scatters o ff an argon nucleus, the nucleus recoils, exciting and ionizing nearby atoms; excitations leads to emission of primary scintillation light (S1). A carefully maintained electric field, established between a cath ode at the bottom and an anode at the top, causes the ionization electrons to drift upward through the liquid. The anode is precisely machined and equipped with adjustment system control to remain flat within tight tolerances (about 100 µ m) to preserve field uniformity. Both anode and cathode are optimized to balance mechanical robustness and optical transparency, operating under a cryogenic environment and important viscous e ff ects. As electrons approach the liquid-gas interface, they encounter a SS extraction grid that produces a strong localized field, pulling the electrons