Influence of Magnetic Elements on an Isochronous Cyclotron Field

One of the main advantages of using magnetic field measuring equipment supported external to the cyclotron magnet is the ability to map the field before and after installation of the extraction elements. Field measurements with extraction elements in place are usually precluded by the size of internally mounted field mapping equipment (e.g., a wheel). The magnetic field of the NRL-isochronous cyclotron was measured to full radius before installation of extraction elements. After installation the influence on the magnetic field of each extraction element energized separately was measured. These measurements were used to determine the perturbation of the extraction channel on the isochronous field. Ion orbit calculations were then used to determine necessary field corrections to accelerate ions to the extraction radius. These field corrections are translated to currents needed in each of the various coils via a least squares fitting program.