Invited Paper-The Separated-Orbit Cyclotron

The separated-orbit cyclotron (SOC) is a cyclic accelerator which combines the advantages of the isochronous cyclotron, the synchrocyclotron, and the linear accelerator. In an SOC, injected ions are accelerated by radio frequency cavities interspersed with the sectors of a magnet structure that guides and focuses the beam along a fixed spiral path. The magnet structure, intersected radially at equal azimuthal intervals by the rf cavities, is designed so that the time per revolution of the particles is independent of their energy, as in an isochronous cyclotron, and it may incorporate any of the well-known methods for focusing ions, such as are used in various types of synchrocyclotrons. The particles accelerated in the SOC are phase focused with respect to a synchronous phase angle corresponding to a chosen rate of energy gain and a peak accelerating voltage. This is made possible by the independent magnetic focusing for the separated orbits since the transverse dimensions of the beam are much smaller than the separation between adjacent turns, 100% beam extraction efficiency should be easily achieved. Variable energy can be obtained by moving the extraction magnet to intercept all of the beam at the right turn for the energy desired. The original concept of the SOC featured a spiral-helix ion path, sometimes called "beehive," Fig. 1, in which the orbit separation necessary to accommodate the independent magnet structure for successive turns was gained mainly by axial displacement.