Faulty Connections in the Beam Position Monitors and their effect on the Beam

In the BE-Newsletter issue 24 in December 2018 it was introduced that the instabilities regarding the PSB extraction kicker were produced by unmatched termination of cables. The same type of vertical instabilities were also seen in LEIR. This was also caused by a mismatch at the strip-line beam position monitors (BPM). A BPM is a device used to measure the position of the beam by measuring the voltage produced by the beam. Comparing the voltage to a BPM on the opposite side, the vertical and horizontal coordinates can be calculated assuming the beam has a Gaussian distribution. The purpose of this project was to study how different terminations e.g. unmatched impedances, shorted or open cables in the BPMs affect the beam and cause instabilities. For this project we were given a test bench version of a BPM as seen in figure 1 which was used for initial measurements. Based on the technical drawings of the device a CST model was also constructed for the purpose of further study. The measurements and the simulation results were then compared to prove that the CST model was accurate enough to be used for further studying of the effects. Many different simulations were performed to obtain the results introduced at the end of this report.