A Study on the Optimization of an HTS Quadrupole Magnet System for a Heavy Ion Accelerator Through Evolution Strategy

This paper attempted to use a high-temperature superconductor (HTS) quadrupole magnet in a heavy ion accelerator. In such application, HTS quadrupole magnets are superior to conventional superconducting magnets because their heat loads can be removed more efficiently. Generally, the magnetic field quality of quadrupole magnets is assessed through harmonic analysis. In quadrupole magnets, the second (four-pole) component is the main magnetic field, and the field inhomogeneity is composed of the sixth (12-pole) component, the tenth (20-pole) component, and so on because of its symmetry. Therefore, the harmonic contents in a good field region can be defined to express the field quality of a quadrupole magnet by using higher order components (order > 2) with respect to the second component. In conventional analysis, multipole components can be obtained by a Fourier series of the radial field component. This paper analyzed the difference between radial and azimuthal multipole components. The HTS quadrupole magnet is wound with a rectangular tape and requires specific structures for refrigeration, which increases the harmonics. In this paper, the effects on the harmonic contents in relation to the HTS coil position and the shape of the iron pole were analyzed based on the HTS quadrupole magnet of the RAON system for the Rare Isotope Science Project in Korea. Several parameters were selected in designing the HTS quadrupole magnet system by using the evolution strategy method. Finally, all harmonic contents were optimized, and an HTS quadrupole magnet design was suggested.