An Inductive Pick-Up for Beam Position and Current Measurements

An Inductive Pick-Up (IPU) senses the azimuthal distribution of the beam image current. Its construction is similar to a wall current monitor, but the pick-up inner wall is divided into electrodes, each of which forms the primary winding of a toroidal transformer. The beam image current component flowing along each electrode is transformed to a secondary winding, connected to a pick-up output. Four pick-up output signals drive an active hybrid circuit (AHC), producing one sum signal, proportional to the beam current, and two difference signals proportional also to the horizontal and vertical beam positions. The bandwidth of these signals ranges from below 1 kHz to beyond 150 MHz, exceeding five decades. Each electrode transformer has an additional turn to which a pulse from a precise current source is applied to calibrate the sensor for accurate beam position and current measurements. The IPU has been developed for the drive beam linac (DBL) of the Third CLIC Test Facility (CTF3). For that purpose it had to be optimized for low longitudinal coupling impedance in the GHz range.