Beam Impedance Optimization of the TOTEM Roman Pots

The TOTEM experiment has been designed to measure the total proton-proton cross section and to study elastic and diffractive scattering at the LHC energy. The measurement requires detecting protons at distances as small as 1 mm from the beam center: TOTEM uses Roman Pots (RP), special beam pipe insertions, to move silicon detectors close to the beams to detect particles very near the beam axis. In the first period of running of the LHC no problems were detected with retracted Roman Pots and during insertions in special runs; however, during close insertions to highest intensity beam, impedance heating has been observed. After the LS1 the LHC beam current will increase and the equipment that can interact with the beam needed to be optimized. A new RP, optimized to minimize the beam coupling, has been designed with the help of CST Particle Studio; a prototype has been used to test the simulation results in the laboratory with wire and probe measurements. Furthermore, in both the old and the new RPs, new ferrites have been installed. The new ferrite material has a higher Curie temperature than the one used before LS1 and a thermal treatment at 1000°C has been applied to reduce the out-gassing.