Beam equipment electromagnetic interaction in accelerators: simulation and experimental benchmarking

One of the most significant technological problems to achieve the nominal performances in the Large Hadron Collider (LHC) concerns the system of collimation of particle beams. The use of collimators crystals, exploiting the channeling effect on extracted beam, has been experimentally demonstrated. The first part of this thesis is about the optimization of UA9 goniometer at CERN, this device used for beam collimation will replace a part of the vacuum chamber. The optimization process, however, requires the calculation of the coupling impedance between the circulating beam and this structure in order to define the threshold of admissible intensity to do not trigger instability processes. Simulations have been performed with electromagnetic codes to evaluate the coupling impedance and to assess the beam-structure interaction. The results clearly showed that the most concerned resonance frequencies are due solely to the open cavity to the compartment of the motors and position sensors considering the crystal in operational position. The numerical modeling is complicated for not-elementary geometry structures, especially when the materials inside the structure have unknown or complex electromagnetic properties. The second part of the thesis illustrates a numerical/experimental methodology benchmark to evaluate the coupling impedance also for complicated structures. A canonical pillbox has been characterized for the validation of this methodology. A comparison among analytical formulas, numerical results and experimental measurements has been performed. The results are encouraging and also applicable to different geometries.