Development of a Measurement Set-up for Testing of RF-Bypasses in the LHC Injector Chain

The CERN, European Organization for Nuclear Research, performs experiments in order to understand the laws of fundamental physics and of the universe. The main machines are particle accelerators, connected as a chain, to achieve a very high energy in the last link, the Large Hadron Collider (LHC). In this circular accelerator, two particle beams travel in vacuum pipes in opposite direction at almost the speed of light and with very high energy (7 TeV) and collide at four precise places, called interaction points where the experiments are located. At these places the interactions are observed to understand the laws of fundamental physics. In this accelerator chain, the two first circular machines, the Proton Synchrotron Booster (PSB) and the Proton Synchrotron (PS) accelerate the particles and increase their energy. The particles are circulating in vacuum chamber beam pipes, which are passing through different machine elements such as; accelerating cavities, beam instrumentation for measuring beam parameters or magnets needed to bend the trajectory of the beams. As the particles are charged, an image current is propagating along the conducting beam pipe. In addition, both machines feature isolated flanges, tightened with clamps, in the beam pipe to avoid that induced currents created e.g., by the magnets are spreading throughout the structure where it could perturb the beam or interact with sensitive measurement equipment. These isolations create an equivalent electrical circuit emitting resonances. Therefore, radiofrequency (RF) filters, so called RF-bypasses, have been integrated into both machines. These filters shift the resonance but also ensure to reduce the contribution to the beamcoupling impedance in the frequency range that is harmful for the beam. It is therefore important to perform annual checks on the functionality of these elements during the shutdown period of the accelerator complex. Because there is a large number of RF-bypasses in both the PSB and PS rings, it is necessary to have a fast measurement system. The measurement system also has to provide a good reproducibility such that a database can be created over the years of all measurements in order to predict RF-bypass failure and to allow for preventive maintenance. This project is split into three main objectives. A LabVIEW application connected to a vector network analyzer (VNA) is developed for a fast measurement and for data storage. A mechanical clamp needs to be created to attach the measurement pin to the structure and improve the reproducibility of the measure for every RF-bypass fixed on the clamp. Finally, a program statistically analyzes all the data collected during the measurement campaign to determine if the bypass is damaged compared to the ideal response over the frequency range. This set-up will be used during the yearly maintenance campaign.