Superconducting maglev systems have been developed in Japan for more than 50 years for use in super-high-speed rail applications, and superconducting maglev trains have been tested on the Yamanashi Test Line in Japan since 1997(1). The superconducting maglev system will be used on the Chuo Shinkansen line(2) as a bypass for the Tokaido Shinkansen line, which connects Japan's three major metropolitan areas. Between Tokyo and Osaka, the system will provide airplane-like speeds while emitting significantly less carbon dioxide than airplanes.
The superconducting maglev system with onboard superconducting magnets with NbTi coils cooled by liquid helium continued its running tests on the Yamanashi Test Line. The onboard NbTi superconducting maglev system has been technically completed, and this low-temperature superconducting maglev system was planned to be put into commercial operation in 2027 as originally scheduled. However, the construction of the line has been delayed, and there is a possibility that the start of commercial operation will be delayed by several years. On the other hand, running tests with bogies equipped with high-temperature superconducting magnets have been conducted since 2005, and the delay in the start of commercial operation has raised the possibility of starting commercial operation with a superconducting maglev system incorporating high-temperature superconducting technology.
The introduction of high-temperature superconducting technology in superconducting maglev systems has several advantages. The superconducting coils are not cooled by liquid helium, but by conduction cooling using refrigerators. As a result, there is no need for liquid helium facilities at the train depots and no need to operate and maintain them. The elimination of liquid helium equipment is a major benefit for the rail operator. In addition, since liquid helium is not used, the structure of the onboard superconducting magnets becomes simpler and more robust.
Onboard superconducting magnets for superconducting maglev trains are constantly subjected to electromagnetic and mechanical disturbances (vibrations) during high-speed operation. Therefore, it is necessary to achieve high stability as a superconducting magnet, to reduce the electromagnetic and mechanical disturbances that cause losses in the magnets, and to improve the magnet design to reduce losses. The current superconducting maglev system with NbTi coils has brought these points to a practical level and is technically complete. High-temperature superconducting coils have the potential to achieve high stability, but it is necessary to demonstrate that this can be achieved with actual high-temperature superconducting coils by conducting sufficient tests, and this is currently underway.
At present, the operating temperature of the high-temperature superconducting magnets is set at about 18 K. If the operating temperature can be further increased in the future, there is a possibility of eliminating the radiation shields in the magnets, in which case the magnetic gap between the superconducting coils and the ground-side guide coils can be reduced. Reducing the length of the magnetic gap leads to improved performance.
In this presentation, the status of the running tests of superconducting maglev trains and the construction of the Chuo Shinkansen will be reviewed, and the application of high-temperature superconducting technology to superconducting maglev trains will be summarized from a technical point of view and discussed, including its future possibilities.
(1) K. Sawada, Outlook of the Superconducting Maglev, Proceedings of the IEEE, Vol. 97, No. 11, pp. 1881-1885, Nov. 2009.
(2) https://scmaglev.jr-central-global.com/