Detuned primary RF coupling system for variable frequency cyclotrons

A new concept of impedance matching for an RF amplifier coupled to a cyclotron cavity, named “detuned primary coupling”, is proposed. It does not require the motion of the coupling loop in vacuum and the matching for different working frequencies is performed by “detuning” the eigenfrequency of the amplifier cabinet alone by means of a variable capacitor. A simple mathematical approach used in the design procedure is presented. Measurements on the 1 : 1 scale model of the VINCY cyclotron RF system have been carried out in the operating frequencies range. The results confirm the viability of the concept and the use of this approach in cyclotron RF amplifier coupling.