ETD

• composite materials
• design of lightweight structure
• finite element analysis
• mechanical structures
• particle accelerator
• static and modal analyses

The Belle II experiment, currently operating at the SuperKEKB collider in Tsukuba,Japan, is designed to explore physics beyond the Standard Model, with a particular emphasis on the study of CP violation in B-meson decays. Achieving the high luminosity required for such precision studies demands a vertex detector capable of combining excellent spatial resolution, mechanical stability, and a minimized material budget. Within this framework, the development of the new Vertex Detector (VTX), based on monolithic CMOS OBELIX sensors, has been proposed to replace the current PXD and SVD systems. This thesis focuses specifically on the mechanical design of the outer VTX (oVTX) support structures, which constitute the outermost layers of the detector, in particular on the optimiziation of the layer six (L6) ladder which is the most mechanical challenging layer. The work begins with an overview of the experimental requirements and environmental constraints, including alignment tolerances, thermal management, radiation hardness,and robustness against mechanical stresses and seismic events. It then addresses the selection of structural materials, the design of ladder prototype, and its assembly processes, with particular attention to minimizing the material budget while ensuring
long-term stability.Then a dedicated chapter presents the experimental tests carried out on the prototype ladder to evaluate their mechanical response under controlled loading conditions.
These measurements are complemented by finite element simulations performed with ANSYS, which allow validation of the design assumptions and guide possible optimizations.The thesis concludes with a discussion of the trade-off to choose the optimized design.The trade-off has been conducted between the material budget evaluation and the minimum ladder deflection, highlighting the balance between mechanical performance and detector transparency requirements.