Improvements in the Michigan State University Cyclotron RF System

A new all solid state dee voltage amplitude regulator has been built for the MSU Cyclotron. It should lead to a factor of two improvement in the energy resolution of the external beam with a consequent increase in the ratio of beam-on-target to internal beam for most experiments. The RF drive to the final amplifier is regulated at a 10 mW level via an FET tetrode amplifier (Fig. 1). The gain of the FET is controlled by a signal proportional to the difference between a reference voltage and the sum of demodulated signals from each dee. Protective circuits are included which remove RF drive to the final amnlifier in the event of severe dee sparking, and limit final grid and anode voltages as guards against clumsy cyclotron operators. Peak-to-peak noise levels of the dee voltage of less than 0.07% are achieved and with careful adjustments noise levels of less than 0.05% have been obtained. Since the cyclotron is usually operated with internal beam pulse-widths of less than 0.5 nsec. corresponding to an energy spread due to phase width alone of 0.04%, noise on the dee voltage makes a significant contribution to the over-all energy resolution of the external beam.