Wide Band Ferrite Beam Current Monitors

A ferrite electron beam current monitor has been developed for use with the NBS Linac. This monitor is useful at the fast rise times (< 5 ns) needed for the short pulsing of the linac and also gives good flat top response for the long pulse (up to 5 μs) work. The low frequency response is achieved by using ferrite with a large μ (= 5000) and a large number of turns (100). At the higher frequencies the core plays a very small role and the structure acts as an air core transformer. The main difficulty observed with other types of ferrite transformer monitors has been ringing due to coil resonances, making these transformers unsuitable for use with fast rise times. This ringing has been eliminated by the placement of damping resistors around the coil and tying them to a common but independent annular ring adjacent to the coil.