title: Investigation of thermal and structural integrity of modules and ladders of Silicon Tracking System of the CBM experiment
Creators: name: Mehta, Shaifali
Publisher: name: Universität Tübingen
Year: 2025
Subjects: subject: 530

description: The Compressed Baryonic Matter (CBM) at the Facility for Antiproton and Ion Research (FAIR) is a fixed target experiment designed to investigate the properties of strongly interacting matter in the region of high net-baryon density. The Silicon Tracking System (STS) is the core detector of the CBM experiment and aims to track and measure the momentum of the charged particles. The STS detector comprises of 876 double sided silicon micro-strip sensors connected via micro cables to the Front-End Boards (FEBs) which are kept outside the detector acceptance of 2.5° to 25°. These sensors are mounted on 106 carbon fiber ladders which includes standard ladders and central ladders with an opening for the beam-pipe. For good particle tracking accuracy in the CBM, the silicon sensors must be mounted on the ladders with extremely high precision, minimizing misalignment and optimizing the spatial resolution of the detector. The experimental operating conditions of STS present challenges to the electronics due to a highly variable thermal environment. A significant portion of the thesis focuses on the thermal studies of the STS components. This involves a detailed investigation of the requirements for thermal interface materials (TIMs) between the FEBs and the cooling shelves. The study includes optimization techniques for adhesive application and thermal testing to ensure the effectiveness of the TIMs. To ensure the reliable functioning of FEBs under significant temperature variations, thermal cycling tests were conducted, and potential failure scenarios have been analyzed. The main focus of the thesis is the understanding of the structural integrity of the STS detector. It is investigated how the STS ladders, essential for supporting the silicon sensors, are put together and how they perform. The design and quality assurance processes for carbon fiber ladders are examined, followed by a step-by-step description of the ladder assembly procedure. The evolution of the ladder assembly procedures, from initial prototypes to fully functional ladders with the required mounting precision are highlighted. The developed procedure is designed to be iterative and easily adaptable for producing 106 STS ladders. The final section of the thesis addresses the vibration challenges encountered by the STS ladders due to air cooling, which is essential for maintaining the sensor performance. It describes the experimental setups used to measure the eigenfrequencies and vibrations on the sensor surface under airflow conditions. The study uses a perforated tube to direct airflow onto the sensor surfaces and highlights the performance differences between the standard and central ladders. Through the analysis of vibration magnitude, the impact of airflow on the stability of the silicon sensors once they are mounted on the ladders, is evaluated. These findings underline the significance of effective vibration control to maintain sensor stability. This thesis provides a comprehensive understanding of both thermal management and structural integrity of the STS. Through extensive testing of TIM and thermal cycling of the FEBs, the last step of the module assembly process has been optimized, resulting in a reliable TIM now used in the series production of the modules. Along this work, significant progress has been made in developing the ladder assembly procedure, which is now being implemented for all the ladders, with series production already underway. The central ladder assembly procedure has been optimized and validated with a prototype ladder. The vibration measurements have established the boundary conditions for airflow through the perforated tube, ensuring the mechanical integrity and necessary cooling to prevent thermal runaway.