Development of a small-size superconducting bulk magnet system especially designed for a pulsed-field magnetization

We developed a small superconducting bulk magnet system that was especially designed for a pulsed-field magnetization. The industrial applications of bulk magnets demand the miniaturization of the magnet apparatus as well as the enhancement of the magnetic field. A Gifford-McMahon cycle helium refrigerator with the ultimate temperature of 13 K at the 2nd stage was adopted, and a GdBa₂Cu₃O_7-x bulk material of 60 mm diameter and 20 mm thickness reinforced by a stainless steel ring was located on a cold stage. The total length of the magnetic pole was 570 mm including the refrigerator, therefore, the system could easily be managed. A cooling test and a magnetizing test were carried out using a Hall sensor and thermocouples adhered on the top surface of the material. In the cooling test, the value of 22.5 K at the cold stage was achieved in 3 h. In the magnetizing test, five successive pulsed-fields of the same strength were applied while changing the applied field, and the time responses of the trapped flux density and temperature were measured at each stage. When a magnetic field of 6.97 T was applied, the trapped field reached 2.04 T, which is the highest ever reported for a pulsed-field magnetization of φ{symbol}60 mm class bulk material.