Magnetically Levitated (MAGLEV) trains are considered as a future application of HTS development. To understand why, we must look briefly at the history of the railroads. The development of trains and rails began in the early 1800s. The modern conventional train is no faster (~110 mph) than those of the late 1890s. So conventional trains have reached the end phase of their development.
France, Germany, and Japan have developed “high-speed” or “bullet” trains capable of speeds of 150-180 mph. This improvement in speed is based upon improved rails and controls. However, this technology has also reached the end phase of its development. One limiting factor for these trains is the expensive and time-consuming maintenance of the rails. So it is the mechanical friction between train wheels and metal tracks that limit this technology. This leads us to the development of the magnetically levitated (no friction) trains. We briefly describe the history of this development.
The idea of MAGLEV transportation has been around since the early 1900s. The benefit of eliminating the wheel/rail friction to obtain higher speeds and lower maintenance costs has great appeal. The basic idea of a MAGLEV train is to levitate it with magnetic fields so there is no physical contact between the train and the rails (guideways).
To get from this simple concept to a real operational system involves enormous technological developments. While there has been no development of MAGLEV trains in the U.S., in Germany and Japan they have developed functioning demonstration trains (in Japan they have one system that has transported over a million people). To date there are no existing construction designs that include HTS magnets, but we will give a brief history of the MAGLEV trains in Japan and Germany to help explain why HTS magnets should be considered in future development.
Two basically different concepts of magnetic suspension have evolved.
- The attractive electromagnetic suspension (EMS) uses electromagnets on the train body which are attracted to the iron rails. The vehicle magnets wrap around the iron guideways and the attractive upward force lifts the train.
- The electrodynamic suspension (EDS) levitates the train by repulsive forces from the induced currents in the conductive guideways.
In both of these systems the levitating magnets are mounted to a number of “bogies” connected to the train body by a secondary suspension system of dampers and springs. However there is a fundamental difference between these two systems. In the EMS system, the “airgap” between the guideways and train magnets is very small (~1/2 inch), whereas the “airgap” in the EDS system may be as large as 8-10 inches. The small airgap of the EMS system implies much more stringent controls to maintain this small gap.
The superconducting magnets that have been used in these MAGLEV systems have been of the low temperature variety. Because these must operated below liquid helium temperature (4.2 K) these are expensive and complex systems. The technological advantage of operating HTS magnets at liquid nitrogen temperatures (77 K) are enormous.