Dimensional tolerance analysis and quality assurance of a particle tracker’s support structure
Year: 2018
Type: dissertation
Abstract: Particle detectors are some of the largest and most complicated devices ever built, that are used to study the smallest building blocks of our universe. Design and construction can take years and engineers and physicists have to guarantee that the detectors finally operate as required. The Large Hadron Collider (LHC) at CERN is being updated to operate at higher luminosities. Consequently, many of the detectors that study the collisions produced by the LHC are being upgraded. In this thesis, an abstracted feature based model is presented for allocating geometric tolerances for a novel support structure of the future tracking detector of the Compact Muon Solenoid (CMS) experiment. This new tracking detector will have a unique section where silicon sensors are mounted in different angular orientations, providing unparalleled track reconstruction efficiency while lowering costs tremendously. The tolerance analysis is based on the functional requirement of hermeticity in the CMS tracker: silicon sensors within each of the tracker’s layers must overlap slightly so that particles cannot traverse a layer without hitting at least one active sensor surface. Imprecisions in the tracker’s real construction geometry cause the sensors to deviate from their nominal positions. This may generate gaps through which particles can traverse without hitting a sensor. Because the CMS tracker is a first-time-right production, with limited or even no possibilities for corrections in the mechanical construction, the composed model of the tolerances is based on worst-case analysis. \n \nThe second part of this thesis is dedicated to quality assurance; the simulated geometric tolerances are utilized to develop accuracy requirements for dimensional measurements. Dimensional measurement plans are presented for the various assembly stages of the studied sub-detector. The chosen measurement methods utilize either a coordinate measurement machine (CMM) when the geometry and dimensions allow it, or photogrammetry. In case of photogrammetry, detailed descriptions are provided as where to position photogrammetric targets to achieve the required measurement accuracies. \n \nAs a result, it is shown that an abstracted feature based model is suitable for synthesizing tolerances of the CMS trackers support structures. Such model can also be integrated into existing software at CERN, to allocate tolerances for other support structures. Additionally, comprehensive dimensional measurement plans have been developed for the quality assurance of the sub-detector.
Source: Aaltodoc (Aalto University)
Author: Janne Huotari
Language: English
Subfield: Mechanical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2900763526