A magnetic quadrupole pick-up for the CERN PS

In the LHC era, there will be a need to monitor and correct betatron mismatch between machines in a non-destructive way. For this purpose, a quadrupole pick-up has been designed for the CERN PS. Originally, the PS was built for much larger beam sizes than now required when generating the LHC beam, but its large physical aperture should be maintained. Because of this large aperture to beam-size ratio, the quadrupole signal component in a standard pick-up design is strongly suppressed with respect to the common-mode signal, and thus demands a very high common-mode rejection in the signal processing. A magnetic quadrupole pick-up has been designed, in which the common-mode rejection is incorporated in the pick-up itself, by virtue of its geometry. The rejection is thus limited only by mechanical tolerances and can therefore be very large. Without the common-mode component, the dominating signal is dipolar, and small when the beam is centred in the pick-up. The dipole and quadrupole signals can thus be separated using a hybrid circuit with only moderate demands on common-mode rejection. Another advantage with a magnetic pick-up is the low output impedance, allowing the use of passive components when forming the quadrupole signal, which is highly desirable in the radiation environment of the PS ring. Simulations and tests of the pick-up and read-out electronics, as well as the first results with real beam are presented.