To float such a heavy weight, it is necessary not only to generate a high magnetic field with a high-strength superconducting magnet but also to raise cooling temperature for efficient operation. Therefore, for the superconducting magnet, RTRI and Furukawa used a "double pancake coil" that (1) uses SuperPower's second-generation high-temperature superconducting wire and (2) has an "armor coil structure," which Chubu Electric Power Co Inc developed.
The internal and external diameters of the double pancake coil are 120mm and 260mm, respectively. It is a pair of flat coils made by rolling a tape-like superconducting wire to form a shape that looks like a sliced Baumkuchen.
RTRI and Furukawa (1) kept the temperature of the coil at 51K (-222°C) with a cooling method based on thermal conduction without using liquid nitrogen, (2) confirmed conduction and a magnetic field with a current of 110A (operation current) and (3) even succeeded in conduction with a current of 163A (the limit of the wire's performance). Also, they conducted a test using the superconducting bulk body and confirmed a levitation force higher than 2t and a high enough strength.
To generate a high magnetic field with the first-generation high-temperature superconducting wire, it is necessary to lower its temperature to 20K (-253°C). On the other hand, the second-generation wire can be operated at 50K (-223°C), enabling to lower cooling cost. RTRI and Furukawa plan to perform another test in which an actual-size flywheel is floated by adding coils.