Impedance measurements and simulations for the LHC and HL-LHC injection protection collimator

This thesis focuses on the study and the data analysis of the Injection Protection Collimator (also Injection Protection Target Dump or TDI), one of the Large Hadron Collider (LHC) collimators at CERN, in Geneva. The last chapters also deal with the Segmented TDI (TDIS), the TDI upgrade for High Luminosity-LHC (HL-LHC). Going more into details, measurements on the TDI - hexagonal Boron Nitride (TDI - hBN, installed in the LHC during run 2015) were carried out. Using the obtained results as an input, two derivations followed: one evaluating the layer resistivity and the other one for its thickness, in order to consider all the possible coating degradations that could occur. The whole range of data obtained from both the derivations was then fed to Impedance Wake 2D (IW2D), a code performing numerical simulations, to attain impedances. Finally, the resulting longitudinal impedance was compared to some measurements performed on the real TDIs, immediately after they were removed from the LHC. The TDI - Graphite, currently installed in the LHC, was analyzed with the Machine Development (MD) carried out in May 2016. The obtained data were filtered and used to estimate the discrepancy between the tune shift we had in the machine and the one obtained with IW2D simulations. The geometry of the TDI was addressed as an important source of mismatch since IW2D does not consider it in its numerical computations. Electromagnetic simulations with CST Studio Suite were carried out to better investigate this aspect, observing the impacts of the longitudinal segmentation in the 3D model and the ones given by asymmetrically positioned jaws. CST simulations were also used to better understand some degradations in the LHC vacuum detected when retracting the jaws to the parking position. The TDIS was still in its designing stage and some parameters have been studied from different points of view. Our interest lied in some of these parameters, such as the modules spacing, the fingers configuration and the absorbers material. Simulations were carried out to investigate the combinations of these parameters’ possible values or configurations and their impact on impedance and tune shift. Some comparison with the LHC impedance model were also carried out, highlighting the case where the simulated impedance was comparable or exceeded the LHC one: the vertical dipolar impedance at injection.