Islam, Zahoor ul (2021) Real-time monitoring and diagnostics of crystal-based collimation of particle accelerator beams. [Tesi di dottorato]

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The beam collimation represents one of the important items for the future upgrade of the Large Hadron Collider (LHC) at CERN. An effective collimation system is particularly required at higher beam intensities, as even a relatively small number of particles impinging on the superconducting magnets can cause quenching (a sudden loss of superconducting condition). Although the currently used collimation system at CERN is working properly, it presents some limitations which can be overcome by future upgrades. One of these limitations is due the particle diffraction from heavy absorbers. An alternative option to the current collimation system at CERN is represented by the use of bent crystals. These latter are expected to be very effective in beam collimation. In fact, they have the advantage to guide halo particles of the beam on a single absorber. This allows the improvements to the cleaning performance as well as to the impedance of the collider as compared to the multi-stage collimation systems, consisting of large blocks made of amorphous material, placed around the beam. In this framework, UA9 Experiment at CERN is carrying on since many years an R&D on various types of crystals. The aim is to find the best solution to overcome the limitations of the currently used collimation system at CERN, in view of future upgrades of the collider. The first part of this PhD work has been devoted, within the UA9 collaboration, to the characterization of some new crystals to be used in LHC and in the Super Proton Synchrotron (SPS) for collimation. The radiation hardness for high energy neutrons were also tested for these crystals. Beam collimation monitoring is performed in the UA9 crystal based system using a Cherenkov detector for high energy protons going through the fused silica. Presently, classical PMTs are in use to collect the Cherenkov light, but its dark count rate is directly affected by the high intensity radiation. With the aim to face this limitation, the second part of this PhD project focused on the characterization of ZnO material, which resulted to be very promising for realizing alternative photodetectors. In this respect, Cherenkov detector/setup used in UA9 could be updated with more functional sensor systems which are radiation resistant and compatible with vacuum requirements in the beam pipe. Another important aspect in collimation systems is the real time monitoring of collimated beams inside the accelerators, especially when using a crystal based collimation system as in UA9. A good approach to face this aspect is to develop a machine learning based real time framework to analyze the signal and detect the faults. The last aim of this work is to present a preliminary study of data acquisition as a starting point to develop a real time framework to be built in the future. This work has been carried out using a SiPM sensor (which competes with the PMTs) with a fast ADC digitizer in real time.

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