Studies on gas systems for particle detectors at the CERN LHC experiments

This work focuses on the operation of the CERN LHC gas systems, which deliver the required gas mixture to the different gaseous particles detectors at the CERN LHC experiments. A fail and a consequent stop of the gas system can lead to loss of data taking during LHC Run. It is therefore fundamental to have a reliability of gas systems close to 100% that can be obtained thanks to proper intensive maintenance and consolidation programs. One of the main task of this work was to develop new standard maintenance proce- dures for each functional module of the gas systems as well as to set-up a LHC-like gas system test bench in a laboratory to faithfully reproduce the operation of a real gas system. This test-bench can be used for training and it will allow to test new or different components as well as software updates. The characterization, optimi- sation and validation of components and new softwares in a laboratory instead of on-site allow reducing time, costs and risks related to the operation. For the devel- opment of the maintenance procedures, the gas system test bench was really useful, for instance making possible to test and validate the procedure itself and, eventually, to improve it. The generic procedure has been divided into three parts, correspond- ing to the different phases and working conditions in which a generic system can be operated. For each phase, an analysis of the required or feasible actions has been performed and for each component the possible failure modes and the correspond- ing best maintenance technique has been identified. Particular attention has been dedicated to leak tests and verification of functionality of the different gas compo- nents. Concerning consolidation and upgrade programs for the LHC gas system, in this thesis the search and validation of new regulation valves for the CMS RPC gas sys- tem has been performed. After having defined all the technical specifications and considered the various constraints, different valves were chosen and tested under different conditions in laboratory in order to find the one which suited the best to the application requirements. Five selected valves were afterwards installed in the CMS RPC gas system and tested under real operation conditions. The study led to a final solution proposal and few more test will be needed to finally validate the se- lected regulation valve. In case of positive outcome, twenty-eight regulation valves will be installed in the CMS RPC gas system distribution module during LS2 period in order to be ready for LHC Run 3.