Beam phase measurement in the AGOR-cyclotron

The AGOR cyclotron is equipped with thirteen phase probes for optimization of the isochronism The beam phase is measured at the 2(nd) harmonic of the RF frequency, in order to be able to suppress the large RF interference from the nearby resonators. At low RF frequencies a phase accuracy of 1 deg. is obtained for a 30 nA beam; at high RF frequencies interference at the 2(nd) harmonic causes a strong degradation of the accuracy. Since good optimization of the isochronism is a critical factor in producing beams of these relativistic ions, alternative schemes for phase measurement are being investigated based on chopping the beam and on injecting at a sub-harmonic of the RF frequency.