First Operation of a Flattop Accelerating System in an Isochronous Cyclotron

In the 590 MeV SIN ring cyclotron a 150 MHz cavity operating on the third harmonic of the fundamental accelerating voltage is now in routine use at average beam currents up to 170 μA. Addition of this cavity resulted in an increased phase acceptance for the single turn extraction mode of over 40° compared to 9° without flattop system. The extraction efficiency is improved from a previous 99.9% to 99.98% while the energy spread is reduced to less than .05% or 300 keV (FWHM). The 150 MHz cavity has a voltage of 350 kV and requires 40 kW of RF power. An important feature is the tight tolerance of .03° on the phase stability.