Surely most of you know something about the posssibilty to greatly increase speed and efficinecy off train transportation - use of MAGLEV trains
(magnetic levitation). Such trains are hoovering above the surface so without contact with the ground their speed can be much higher than by
There were originally two MAGLEV solutions : German one Japannesse ones.
The German maglev
uses conventional electromagnets 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. THis makes the train very expensive so only one known example is built in Shanghai.
- electrodynamic system (EDS), large superconducting magnet coils mounted on the sides of the train generate high-intensity
magnetic field poles. Interaction of the current between the coils and the track levitates the train. At operating speeds the magnetic levitation
force balances the weight of the car at a stable position. EDS trains do not require the feedback control systems. However, the superconducting
magnetic coils must be kept at temperatures of only 5 kelvins, so costly electrically powered cryogenic equipment is required. Also, passengers must
be shielded from the high magnetic fields generated by the superconductors.
As you see this requirements make the MAGLEV too expensive for use. But now Lawrence Livermore scientists have recently developed a new approach to
magnetically levitating high-speed trains that is fundamentally much simpler in design and operation Inductrack
How does it work
The new system is passive in that it uses no superconducting magnets or powered electromagnets. Instead it uses permanent room-temperature magnets,
similar to the familiar bar magnet, only more powerful. On the underside of each train car is a flat, rectangular array of magnetic bars called a
Halbach array. (It is named after its inventor, Klaus Halbach, a retired Lawrence Berkeley National Laboratory physicist.) The bars are arranged in a
special pattern, so that the magnetic orientation of each bar is at right angles to the orientations of the adjacent bars [see top illustration on
this page]. When the bars are placed in this configuration, the magnetic-field lines combine to produce a very strong field below the array. Above the
array, the field lines cancel one another out.
The second critical element is the track, which is embedded with closely packed coils of insulated wire. Each coil is a closed circuit, resembling a
rectangular window frame. The Inductrack, as its name suggests, produces levitating force by inducing electric currents in the track. Moving a
permanent magnet near a loop of wire will cause a current to flow in the wire, as English physicist Michael Faraday discovered in 1831. When the
Inductrack's train cars move forward, the magnets in the Halbach arrays induce currents in the track's coils, which in turn generate an
electromagnetic field that repels the arrays. As long as the train is moving above a low critical speed of a few kilometers per hour-a bit faster than
walking speed-the Halbach arrays will be levitated a few centimeters above the track's surface.
The magnetic field acts much like a compressed spring: the levitating force increases exponentially as the separation between the track and the train
car decreases. This property makes the Inductrack inherently stable-it can easily adjust to an increasing load or to acceleration forces from rounding
a bend in the track. Thus, the system would not require control circuits to maintain the levitation of the train cars. All the train would need is
some source of drive power to accelerate it.
In the past, engineers believed permanent magnets could not be used in maglev systems, because they would yield too little levitating force relative
to their weight. The Inductrack's combination of Halbach arrays and closely packed track coils, however, results in levitation forces approaching the
theoretical maximum force per unit area that can be exerted by permanent magnets. Calculations show that by using high-field
alloys-neodymium-iron-boron, for example-it is possible to achieve levitating forces on the order of 40 metric tons per square meter with magnet
arrays that weigh as little as 800 kilograms per square meter, or one fiftieth of the weight levitated.
PERMANENT MAGNETS under an Inductrack train car are arranged in a Halbach array (above) so that the magnetic-field lines reinforce one another
below the array but cancel one another out above it. When moving, the magnets induce currents in the track's circuits, which produce an
electromagnetic field that repels the array, thus levitating the train car.
In a full-scale Inductrack system, the track would consist of two rows of tightly packed rectangular coils, each corresponding to one of the steel
rails in a conventional track. The main levitating Halbach arrays would be placed on the underside of the train car so that they would run just above
the rows of coils. Smaller Halbach arrays could be deployed alongside the rows of coils to provide lateral stability for the train car. Such a
configuration would somewhat resemble its counterpart in an ordinary train-namely, a flanged wheel rolling on a steel rail. In the Inductrack the role
of the "flanges" is played by the small side-mounted Halbach arrays, whereas the role of the "wheel" is fulfilled by the main levitating
Halbach arrays can also provide lateral stability if they are deployed alongside the track's circuits (below).
A primary concern for any maglev is the efficiency of the levitating system. Unlike the German and Japanese maglevs, the Inductrack requires no power
to produce its magnetic field, because it uses permanent magnets. Therefore, this particular source of inefficiency is not an issue. To levitate the
train car, though, currents must be induced in the track's circuits, and electrical resistance in the circuits will dissipate some of the power,
converting it to heat
WORKING MODEL of the Inductrack constructed at Lawrence Livermore National Laboratory to test the system's performance. The first section of the
20-meter-long track contained electrically powered drive circuits to accelerate a 22-kilogram cart (below). Once set in motion, the Halbach arrays on
the underside of the cart allowed it to coast over the 1,000 levitating coils in the second section of the track.
A preliminary feasibility study concluded that a full-scale Inductrack system would be less expensive to build and operate than the German maglev.
For example, the study estimated that a train car equipped with Halbach arrays would cost between $3.2 million and $4.2 million, whereas a car in the
German maglev would cost more than $6 million. (The estimated cost of a Japanese maglev car has not been made available.) The Inductrack vehicle would
be more expensive than a conventional railcar, which costs between $2 million and $3 million, and building the system's track could cost as much as
80 percent more than constructing an ordinary track. The study noted, however, that the Inductrack's energy usage and maintenance costs would be
significantly lower than those of a conventional railway.
Other aplications - rocket launch?
NASA awarded the laboratory a contract to build another model, aimed at demonstrating a very different application of the Inductrack concept. Studies
by NASA have shown that if their rockets could be accelerated up a sloping track to speeds on the order of Mach 0.8 (950 kilometers per hour) before
the rocket engines were fired up, it could substantially cut the cost of launching satellites. Such a system could reduce the required rocket fuel by
30 to 40 percent, thereby making it easier for a single-stage vehicle to boost a payload into orbit. Our Inductrack model, which will have a track
about 100 meters long, will be designed to accelerate a 10-kilogram "launch cradle"-the rocket's platform-to speeds of about Mach 0.5 (600
kilometers per hour). Because of the shortness of the test track (compared with the kilometer-or-so length of a full-scale system), the electrical
drive circuits for the NASA model must achieve 10-g acceleration levels. In a full-scale system the acceleration levels, limited by the strength and
weight of the rocket itself, would be more modest, on the order of 3 g's.