Beam Phase Detection with a Fixed Intermediate Frequency System at JULIC

In order to measure the beam phase in the cyclotron at low beam currents, a system has been developed which works well even in presence of severe HF-disturbance. By mixing and filtering techniques two fixed high frequency signals are derived and fed to a phase detecting circuit formed by double balanced mixers. Using a fixed frequency and applying a double compensation of the HF-disturbances, the system is able to analyse beam signals of less than 10-3 of the disturbing voltage. The capacitive phase probes are built in 50 ohm technique, which in principle allows the extension of their azimuthal length up to the optimum value. A special real time display of the beam phase and the intensity on a scope are provided.