Maglev: A New Approach; January 2000; Scientific American Magazine; by Post; 6 Page(s)
The story "Prince Ahmed and the Fairy," one of the classic tales in The Thousand and One Nights, tells of a prince who flew from place to place on a magic carpet, supported by invisible forces. The modern version of the magic carpet is the magnetically levitated train, or maglev, which can travel faster and more efficiently than ordinary trains because it rides on air instead of steel rails. The concept took off in the late 1960s, when Gordon T. Danby and James R. Powell of Brookhaven National Laboratory proposed using superconducting coils to produce the magnetic fields that would levitate the trains. In the 1970s and 1980s demonstration maglevs were built in Germany and Japan. Yet despite the appeal of the technology, which promises smooth-as-silk train rides at speeds up to 500 kilometers per hour, no full-scale commercially operating maglev system has been constructed.
Why is this so? For one, the maglevs that have been demonstrated so far are much more expensive and complex than conventional railways. The Japanese system, for example, requires costly cryogenic equipment on the train cars to cool the superconducting coils, which must be kept below about five kelvins to operate efficiently. The German maglev uses conventional electromagnets rather than superconducting ones, but the system is inherently unstable because it is based on magnetic attraction rather than repulsion. Each train car must be equipped with sensors and feedback circuits to maintain the separation between the car's electromagnets and the track. What is more, neither system is fail-safe. A breakdown of the magnet control circuits or power systems could lead to a sudden loss of levitation while the train is moving. Careful design can minimize the hazards of such a failure but not without a further increase in cost and complexity.