Design considerations for a separated turn isochronous cyclotron

Abstract

The objective of this machine is the production of large proton currents at energies from 200 to 1000 MeV with clear turn separations so that 100% beam extraction is achieved. Each stage of the cyclotron consists of a “ring” of identical magnet sectors interpersed with an appropriate set of rf acceleration cavities. The beam is injected from a linac thereby eliminating the central region problems associated with present isochronous cyclotrons. As a result of the narrow magnet gaps, the machine has relatively strong axial focusing throughout. The orbital frequency is high enough so that the beam can be accomodated within the space charge limits. Additional small third harmonic cavities provide for a “flat-top” on the resultant voltage wave form thereby allowing a relatively large phase width in the accelerated beam. Conditions for achieving clear turn separation are analysed and found feasible. For a reasonable total number of turns, the isochronous field trimming requirements are quite tractable. Tentative design figures are presented and compared with the present Separated Orbit Cyclotron (SOC) designs.