Stripping extraction of positive ions from a cyclotron

Abstract

In a multipurpose cyclotron, it is convenient to use stripping extraction to extract selected positive ions in addition to the usual extraction by stripping of negative ions. The ions are specified as positive or negative according to the sign of their charge during acceleration. After stripping, positive ions travel not only through the pole edge magnetic field gradient, as is the case with negative ions, but can also pass more than once through regions of large sector edge magnetic field gradients. Influence of the magnetic field gradients on the trajectory of a stripped positive ion and on the extracted beam emittance is studied. It is shown that extraction efficiency depends on the position of the point of beam extraction from a cyclotron and on the ratio between ion charge after and before stripping. The position of the point of extraction also strongly affects the design parameters of the stripping extraction system. Extraction quality and design parameters cannot all be simultaneously optimized. The method of extraction system optimization is suggested and applied to the special case of the VINCY cyclotron.