Magnetic Analysis on the Design of Superconducting Magnet for Developing 28-GHz ECR Ion Source

Since 2011, the Institute for Basic Science has been developing a linear accelerator, called RAON, for a rare isotope science project. The linear accelerator utilizes an electron cyclotron resonance (ECR) ion source for generating intense highly charged ion beams. A superconducting magnet system for a 28-GHz ECR ion source consists of six hexapole coils nested inside four solenoid coils made with low-Tc superconducting wires of NbTi. The superconducting magnets provide an axial magnetic field from four solenoid coils and a radial magnetic field from six hexapole coils to extract an ECR plasma stream that controls the flow current. The electromagnetic force acts on the superconducting magnets due to the magnetic field and flowing current. Therefore, electromagnetic characteristics of the superconducting magnets should be analyzed to minimize the electromagnetic force that causes coil motions and coil strains during excitation. In this paper, the design of superconducting magnets for a 28-GHz ECR ion source is deduced by analyzing the magnetic field to extract intense highly charged ion beams and an electromagnetic force to minimize coil motions and coil strains. The arrangement of the superconducting magnets is inferred by analyzing the magnetic field and the electromagnetic force. Also, the application of an iron pole is considered to improve the stability with a lower operating current. Analysis is conducted by using finite element method simulation.