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Newly introduced particle accelerators such as the Large Hadron Collider (LHC) of CERN (Geneva, CH) exhibit a huge increase in the energy stored inside the accelerated beam with respect to previous machines, bringing to the need of more efficient, reliable and robust Collimation. The research on new materials for Beam Intercepting Devices (BID) is therefore receiving strong interest at CERN and in the rest of the particle accelerator’s community with the aim to improve the cleaning efficiency and the robustness of BID. In that framework the aim of the present PhD work is to develop, characterize and produce new composite materials to be used in LHC Collimators active part that must satisfy multiple requirements in terms of: density and average atomic number, electrical conductivity, thermal conductivity, thermal expansion and robustness against accidental beam impacts. In addition, since the material will be heavily irradiated during its life cycle, it must not contain elements that create dangerous isotopes and must be able to withstand high cumulated doses before to lose its properties by radiation induced degradation. The thesis work has been divided into two main multi-disciplinary axes that are strongly interconnected between each other: the novel composites R&D; and their characterization in standard conditions and the experimental testing of proposed materials against a real proton beam impact. The first part included a preliminary study of present solutions and available composites, the characterization of already developed materials and finally the research, development and characterization of new Molybdenum based composites, which has been carried out in collaboration with the private company BrevettiBizz (Verona, IT) between 2011 and 2013. Molybdenum has been chosen as the main element because of its extraordinary mechanical properties combined with very high Thermal Stability and a good chemical affinity with carbon materials like diamond and graphite. The most important milestones in the materials R&D; presented in the thesis work are Molybdenum - Copper - Diamond (MoCuCD), Molybdenum Carbide - Graphite (MoGR) and Molybdenum Carbide - Graphite - Carbon Fibers (MoGRCF). MoGRCF stands out as promising BID material because of an excellent combination of thermal and physical properties. The material is obtained by Liquid Phase Sintering of Mo, graphite and carbon fibers at high temperature: the reaction between Molybdenum and graphite promotes the complete transformation of Molybdenum in carbide Mo2C, electrically conductive and refractory (TM >2500C). The result is an outstanding material with a thermal conductivity in excess of 700 W/mK and a density of only 2.8 g/cm3. The second part of the thesis is the final testing of proposed materials against a direct beam impact to compare the different collimator materials in a real-life accidental situation., supported by numerical simulations of the beam impacts. The experiment took place into the HiRadMat facility at CERN (High Radiation to Materials) during September-October 2012, entailing the controlled impact on 6 different Collimator materials with increasing proton beam intensities of the Super Proton Synchrotron particles accelerator of CERN (operating at 440 GeV). The energy of the impacts was enough to observe the samples explosion by high speed video camera (during the high intensity shots) and the observation of macroscopic damage on impacted samples. The proposed comparison of the different materials will be the background for the final choice of the LHC Collimator materials to be taken in next years at CERN. |
