Axial injection in the Orsay project of a superconducting cyclotron and in the medical cyclotron MEDICYC

Central geometry compatible with an axial injection has been designed for two cyclotrons : the Orsay project of a superconducting cyclotron (K/subB/ = 600, K/subF/ = 220 and R/subE/ = 0.87 m) and the medical cyclotron MEDICYC (K/subB/ = 60, fixed RF frequency = 24 MHz) now under construction. A design was achieved to fulfill for each case the following requirements : on axis injection, constant geometrical set-up compatible with the various harmonic modes, vertical electrical field components less than 25 kV/cm in the inflector. General considerations on forbidden rho-band (rho = injection radius) are given, which establish clearly the matching conditions of a certain central region to one of the usual inflector types : spiral, mirror, hyperboloid. Thus a mirror has been set up for the first case, and a spiral type, allowing higher injection energy, for the second case. Acceptances in the superconducting cyclotron has been deduced, showing the need of an external source with good emittance and a careful design of the beam transport along the axis of the cyclotron