A single-turn extraction study for the RIKEN superconducting ring cyclotron

The superconducting ring cyclotron which will be built at RIKEN needs to accelerate high-current heavy ion beams for ample production of radio-isotope beams. Beam extraction out of such a cyclotron should be carried out with a low loss to avoid the heating and radiation problems by stray beams. To enhance the last-turn separation the beam will be injected off-centered. And to ensure well-defined turns, it is crucial to maintain the quality of the radial phase space, but difficulties arise for beams traversing the V-r=3/2 resonance. After the resonance traversal, the beam phase space mismatches with a new eigen-ellipse when a third harmonic gradient exits. Correction of the error fields is planned to be made with harmonic excitations of the main and trim coils. In addition, space charge effect may hinder the high-current acceleration with disturbed turn structure. The linear component of its force could be compensated by tuning of a flat-topping cavity.