Analysis of balanced and unbalanced signal transmission lines and noise reduction technique for beam-current monitor in linear accelerators.

A signal transmission line and its characteristics were analyzed in detail for a beam-current monitor (CM) for long-pulsed electron beams. The monitor was based on a conventional current transformer, which comprised an induction coil wound around a ferrite core. The signal transmission and noise generation mechanism were analyzed by theoretical models based on balanced and unbalanced coaxial transmission circuits to effectively reduce noises superimposed on the beam-current signal waveform. The results of numerical analyses based on the theoretical models were in good agreement with those of an experiment for verification. It was found that the noise signals were generated by a high-power klystron operation and they were mode-transformed on the way to the transmission line. These results show that the locations of the grounded points in the transmission line were important. Based on a symmetrically configured three-line circuit theory, a new highly symmetrically configured coaxial transmission line is proposed to effectively suppress noises generated in CM. This report describes in detail the numerical and experimental analysis of a signal transmission line with coaxial cables for CM where the noise generation mechanism and its reduction technique are deeply involved.