First tests of new levitating railway using superconductors

Levitating railways have long been the dream of many engineers: silent as a mouse, with no frictional resistance and low demand of energy compared with conventional trains.

These are just a few advantages magnetic levitation, or Maglev, railways have in comparison to other means of transport.

Only a few Maglev trains have been built so far; most of them are used just to connect two specific places like an airport and the city centre.

But with the development of SupraTrans II by the Leibniz Institute for Solid State and Materials Research Dresden (Germany) we might be a small step closer to whole networks of maglev trains.

The team of researchers, headed by Professor Ludwig Schultz, are testing a maglev train that works with a superconductor.

Superconductors are materials whose electrical resistance shrinks to zero when the material is cooled below a certain temperature.

Superconductors can be used for maglev trains because of the physical phenomenon called the Maissner effect. When the superconductor is cooled below its critical temperature, it levitates in a stable position inside a magnetic field.

Professor Schultz and his colleagues used this principle for the development of their SupraTrans II train, a 330kg heavy carriage which can accommodate two people.

The SupraTrans II works with four superconductors, which operate as the “wheels” of the train. The track is two rails of strong permanent magnets.

Every superconductor is placed at the bottom of a small tank, which gets filled with liquid nitrogen. Since the temperature of the nitrogen is below the superconductor’s critical temperature, the train levitates above the tracks.

The characteristics of the Maissner effect guarantee that the train can only be moved in the direction of the tracks, and not to the sides. So even if the track makes a curve, the magnetic levitation train does not need to be steered, but simply floats in the magnetic field fixed above the rails.

From this near-frictionless position it can easily be driven by an electric motor. The nitrogen tanks have to be refilled just once a day.

The big difference between this MagLev systems and the ones build so far is, that it has no need for electricity to make the train levitate.

There are only three maglev trains running which serve the general public, all of them based in Asia. Unlike SupraTrans II, they use electro-magnets instead of permanent magnets and therefore need additional energy for the train tracks and not just for the train itself.

One example is the Shanghai Maglev Train or Shanghai Transrapid, which connects Shanghai Airport with the outskirts of the city.

The system was built by the German company Siemens, who also tried to sell the Transrapid system to Munich, aiming to connect the Central Train Station with Munich Airport. This was ultimately scrapped because of exploding costs.

The Transrapid works with electro magnets installed in the tracks which make the train levitate above them. A report published in the Swiss journal Eisenbahn Reveu International (train bulletin international) calculated the energy needed for this amounts to 1.7 kilowatt per 1000 kilogram.

So just making the train levitate takes a lot of energy, and the energy needed for accelerating and decelerating the train is not included in this calculation.

For the SupraTrans II, this huge amount of energy is replaced by fluid nitrogen and the Maissner effect.

At the moment, the researchers from the Leibniz Institute for Solid State and Materials Research Dresden (Germany) are testing The SupraTrans II on an 80 metre long track that includes curves and a control system to allow several carriages to run on the track at once.

The maximum speed for testing is about 20kmph; mainly for safety reasons. In theory the system has no speed limit.

If SupraTrans II passes all tests, Professor Schultz believes, this system could someday replace our public transport with a network of independent carriages all over the city.

You could book a carriage for your commute to and from work, and in between someone else could use it.

But while this is still a dream of the far future, more realistic applications within the next few years are smaller networks at airports for example. The carriages could move passengers or luggage quickly from one terminal to the next.

Images by IFW Dresden and Yosemite respectively

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