Optimisation of a Magnetic Quadrupole Pick-up Structure using HFSS

A magnetic quadrupole pick­up has recently been designed for the CERN proton synchrotron. The design is based on a new idea, where the undesired common mode signal is suppressed by coupling to the radial component of the field. One design detail is a thin resistive layer between the beam and the actual pick­up structure. This layer serves to lower the longitudinal impedance, but also influences the coupling impedance of the pick­up. To optimise the design, a series of simulations of the pick­up structure have been performed using the HFSS program. The longitudinal impedance was determined by simulating the coaxial wire­method, and the pick­up coupling to the different field modes created by the ''beam'' was studied and optimised. In this paper, the simulations are presented together with some comparative measurements.