Multidisciplinary approach to the structural, hydraulic, and mechanical design of a steel decay vessel for the SHiP experiment at CERN

In March 2024, the Search for Hidden Particles (SHiP) experiment and its associated Beam Dump Facility (BDF) were selected for future physics exploitation using the Super Proton Synchrotron (SPS) at CERN. SHiP is a general-purpose, intensity-frontier experiment designed to search for dark matter-related physics. Proposed approximately a decade ago, the SHiP experiment has passed through multiple design stages and optimizations. This study focuses on the structural design of primary subcomponent of SHiP, i.e., “the decay volume”, where the experiment seeks decay signatures of new particles. Initial concepts included a reinforced-concrete structure with hollow rectangular cross-sections exceeding 10 m × 5 m, evolving to a 50-m-long conical steel vessel under vacuum, and more recently to a metal-framed helium balloon, which is a textile helium seal supported by steel frames. We present the structural and hydraulic configurations now considered the final reference solutions for decay vessel of the SHiP to highlight the unique engineering challenges of minimizing structural mass, thereby reducing particle interactions and enhancing physics performance. To provide context, the paper first summarizes the collaboration status of SHiP and subsequently reviews the sequence of decay vessel structural options explored since the inception of the project. This historical overview depicts how the decade-long, multidisciplinary effort shaped current design choices. Furthermore, it illustrates how a novel, multidisciplinary, integrated approach guided the design evolution of the decay vessel. In the context of large-scale international collaborations such as SHiP, this paper demonstrates that a coordinated strategy integrating structural, hydraulic, and detector requirements has seldom been applied in similar large experimental facilities. As demonstrated in this study, such an approach proved essential for achieving a configuration that satisfies engineering constraints while preserving the experiment’s physics performance goals. The principal outcome of this effort is the proposed final design strategy, which coalesces engineering and physics goals into a unified framework. This methodology ensured that all subsystem interactions were considered concurrently to prevent costly redesigns during project execution. The final design strategy separates the mechanical system of the decay vessel into two key components: (i) a structural steel framework and (ii) non-structural aluminum elements, both integrated with a complex hydraulic system to circulate a specific detection liquid. This division maintains functional and structural efficiency and offers flexibility to adapt to seismic-condition variations throughout the project.