Air-core high-temperature superconducting quadrupole magnets (AHQMs) differ from conventional iron-core quadrupole magnets, in that their iron cores are removed, and instead high-temperature superconductors (HTSs) are applied. The high operating temperature and high thermal stability of HTS magnets can improve their thermodynamic cooling efficiency. Thus, HTS magnets are more suitable than low temperature superconducting magnets for withstanding radiation and high heat loads in the hot cells of accelerators. AHQMs are advantageous because they are compact, light, and free from the hysteresis of ferromagnetic materials, due to the removal of the iron-core. To verify the feasibility of the use of AHQMs, we designed and fabricated a 3.0 T/m AHQM. The magnetic field properties of the fabricated AHQM were evaluated. Additionally, the characteristics of the air-core model and iron-core model of 9.0 T/m were compared in the scale for practical operation. In comparison with the iron-core model, AHQM significantly reduces the critical current (I C ) due to the strong magnetic field inside the coil. In this study, a method for the accurate calculation of I C is introduced, and the calculated results are compared with measured results. Furthermore, the optimal shape design of the AHQM to increase the critical current is introduced.Electronics 2020, 9, 450 2 of 22 Because of these advantages, including the thermal stability of HTS, as an example, it has been reported that in the Rare Isotope Science Project for the construction of a heavy-ion accelerator called RAON in Korea, six HTS quadrupole magnets will be installed in succession for beam focusing at the front region of the IF pre-separator [7]. Additionally, HTS quadrupole magnets using air-cores have many advantages for heavy-ion accelerator applications, because of the elimination of the iron-core of the conventional HTS quadrupole magnet. Quadrupole magnets with a removed iron-core are advantageous because of their compactness and lightweight, and they are free from the hysteresis of ferromagnetic materials. Therefore, a new quadrupole magnet has been proposed with two differences [8]: replacing the LTS with the HTS wires, and removing the iron-core. As an initial study to replace the existing quadrupole magnets, the effects of the manufacturing error, and the comparison of the characteristics with the iron core, were performed [9,10]. However, no case has been reported on the construction and operation of quadrupole magnets using HTS wires detached from the iron-core. Therefore, research should precede the manufacturing of air-core quadrupole magnets, and the analysis of the magnetic field properties based on the magnetic field measurements. To verify the feasibility of the air-core HTS quadrupole magnet, we designed and fabricated an air-core high-temperature superconducting quadrupole magnet with a field gradient of 3.0 T/m, an effective length of more than 200 mm, and a uniformity of less than 1%. We also fabricated a field mapper to measure the field quality of ...
