Effect of Screening Current Induced Field on Field Quality of an Air-Core HTS Quadrupole Magnet

An air-core high-temperature superconducting (HTS) quadrupole magnet has many advantages for heavy-ion accelerator applications due to the elimination of the iron-core of a conventional HTS quadrupole magnet. It is compact, lightweight, and free of hysteresis of a ferromagnetic material. In our previous study, an air-core HTS quadrupole magnet of 3.0 T/m field gradient was designed. It was composed of eight double-pancake racetrack coils, each wound using 4-mm wide HTS tapes. In the magnet design, a uniform current density was assumed in the HTS tapes. However, in the HTS racetrack coils, magnetization currents are induced by the magnetic field component perpendicular to the tapes, and the magnetization currents generate the so-called screening current induced field (SCIF). For the quadrupole magnet, the SCIF could be critical to the field quality of the magnet. In this study, the current density distribution was calculated considering the magnetization current. Furthermore, the effect of the SCIF on the field quality of the magnet is analyzed and discussed.