Detector and System Developments for LHC Detector Upgrades

The future Large Hadron Collider (LHC) Physics program and the consequent improvement of the LHC accelerator performance set important challenges to all detector systems. This PhD thesis delineates the studies and strategies adopted to improve two different detector technologies: the replacement of precision trackers and the improvement of large muon systems. Within the LHC tracker upgrade programs, the ATLAS Insertable B-layer (IBL) is the first upgrade of a silicon-pixel detector. The IBL Detector makes use of innovative technologies, which required complex developments and thorough quality assurance protocols for the characterization and selection of the best 14 IBL staves. During the High Luminosity LHC phase the muon systems will be pushed close to their operation limits by the increased luminosity and high radiation environment. In this context, several aspects of gas systems and detectors operation have been studied, as the importance of robust and precise gas quality monitoring tools and strategies to reduce detector gas emissions

Studies of IBL wire bonds operation in an ATLAS-like magnetic field and evaluation of different protection strategies

At the Large Hadron Collider (LHC) experiments, most of silicon detectors use wire bonds to connect front-end chips and sensors to circuit boards for the data and service transmissions. These wire bonds are operated in strong magnetic field environments and if time-varying currents pass through them with frequencies close to their mechanical resonance frequency, strong resonant oscillations may occur. Under certain conditions, this effect can lead to fatigue stress and eventually breakage of wire bonds. Systematic studies have been conducted to analyse the effects of resonance vibration on wire bonds. In particular, the case of the Insertable B-Layer (IBL) detector, the new innermost layer of the ATLAS Pixel Detector, has been reviewed. An experimental set-up has been built to simulate as much as possible the operation conditions of IBL wire bonds in the ATLAS magnetic field. The results provide useful information for the comprehension of the IBL wire bonds behavior. The dangerous resonance frequencies have been identified experimentally for different wire bond lengths. The resonance frequency amplitudes have been characterized in terms of several parameters, like wire length, wire orientation angle with respect to B-field and current amplitude. Several fatigue studies have been performed with simulations and laboratory tests. It has been demonstrated that in well-defined conditions, as for example with high currents, the wires can get irreparably damaged after few oscillation cycles and they can break. Two types of wire bond protections have been considered: the classical encapsulation of the wire feet and the coating of the whole wire. The results reveal that these methods minimize the oscillation amplitude reducing the possibility of damaging or breaking the wire bonds. For the IBL detector a Fixed Frequency Trigger Veto has been implemented for excluding the potentially dangerous frequencies identified in these studies

Gas Mixture Monitoring Techniques for the LHC Detector Muon Systems

At the LHC experiments the Muon Systems are equipped with different types of gaseous detectors that will need to assure high performance until the end of the LHC run. One of the key parameters for good and safe long-term detector operation is the gas mixture composition and quality. Indeed a wrong gas mixture composition can decrease the detector performance or cause aging effects and irremediable damages. It is therefore a fundamental requirement to verify and monitor the detector gas mixture quality. In the last years several gas monitoring techniques have been studied and developed at CERN to automatically monitor the detector gas mixture composition as well as the impact of gas quality on detector performance. In all LHC experiments, a gas analysis module allows continuous monitoring of O$_2$ and H$_2$O concentrations in several zones of the gas systems for all muon detectors. More sophisticated and precise gas analyses are performed with gas chromatograph and mass spectrometer devices, which have sensitivity at the level of ppm and allow to verify the correctness of the gas mixture composition. In parallel to standard gas analysis techniques, a gas monitoring system based on single wire proportional chamber has been implemented: these detectors are very suitable to detect any possible aging contaminants thanks to their high sensitivity

Performance studies of RPC detectors operated with C2_2H2_2F4_4 and CO2_2 gas mixtures

Resistive Plate Chambers detectors are largely employed at the CERN LHC experiments thanks to their excellent trigger performances and contained costs. They are operated with a gas mixture made of 90%–95% of C2H2F4, that provides a high number of ion–electron pairs, about 5% of i-C4H10, that ensures the suppression of photon-feedback effects, and 0.3% of SF6, used as an electron quencher to further operate the detector in streamer-free mode. C2H2F4is known to be a Greenhouse gas, with a global warming potential (GWP) of 1430. CERN has identified several strategies to reduce the consumption of greenhouse gas emissions from particle detectors at LHC experiments. One research line is focused on the study of alternatives to C2H2F4. In this context, a conservative approach for the next years of LHC operation could be to focus on reducing the GWP of the RPC gas mixture by only adding CO2 and not using new gases, whose effects on detector long-term operation have to be studied. The RPC performance with standard gas mixture with the addition of 30%–50% of CO2 (and SF6 concentration between 0.3 and 0.9%) were studied both in laboratory set-up and at the CERN Gamma Irradiation Facility in presence of muon beam and gamma background radiation. Encouraging results were obtained showing that the addition of CO2 to the standard gas mixture can represent a mid-term solution to reduce emissions and lower operational costs by keeping stable detector performance and safe long-term operation