A CURRENT MODE INDUCTIVE PICK-UP FOR BEAM POSITION AND CURRENT MEASUREMENT

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 into a secondary winding, connected to a pick-up output. Such sensors are operated in the CERN CTF3 Drive Beam Linac [1]. This paper describes a similar device developed for the CERN Linac 2 to PSB transfer line. To cope with two orders of magnitude longer beam pulses, the new sensor is operated in current mode. The transformers drive transresistance amplifiers (TRA), converting transformer currents into voltages, which in turn are processed by an active hybrid circuit (AHC), producing one sum (Σ) signal, proportional to the beam current, and two difference (∆) signals proportional also to the horizontal and vertical beam positions. The bandwidth of the Σ and ∆ signals spans 6 and 5 decades, respectively. The transformers have an additional one-turn winding to which a pulse from a precise current source can be applied to calibrate the sensor.