THE Inductrack magnetic levitation
(maglev) system, conceived by Livermore physicist Richard Post
as a safer, cheaper, and simpler means to levitate urban and high-speed
trains, is moving down the development track on the way to a full-scale
demonstration. Using unique configurations of powerful, permanent
magnets, called Halbach arrays, to create its levitating fields,
Inductrack is under development by General Atomics (GA) in San
Diego. The project is sponsored by the federal government to showcase
a new generation of urban transportation technology. Recently,
GA and Catherine Elizondo of Livermore’s Industrial Partnerships
and Commercialization Office have signed a licensing agreement
for use of the levitation technology in Magnetic Levitation Train
and Transit Systems.
was conceived by Post in the mid-1990s as a new type of maglev
technology, one that would use Halbach arrays located on the underside
of train cars. (See S&TR, June
1998, A New Approach for Magnetically Levitating Trains—and
Rockets.) The magnetic fields generated by these arrays interact
with a track
composed of shorted circuits to create levitating and centering
magnetic forces. The system is fail-safe upon loss of power, and
simpler and lower in cost than current maglev systems.
Inductrack concept for mass transportation was first demonstrated
at Livermore in 1998 with a subscale model using a 22-kilogram
levitated test cart and a 20-meter-long track. Early Inductrack
work was funded by the Laboratory Directed Research and Development
Program. The tests were so successful that the National Aeronautics
and Space Administration (NASA) awarded the Laboratory a contract
to study the technology as a means to help launch rockets into
space. The rockets would be sent up an inclined slope to about
Mach 0.8 before firing. Post’s team built a second test track
to investigate the rocket-launch idea; the track was shipped to
a NASA contractor this year. The Inductrack will be set up and
tested by engineering graduate students at the Florida Space Institute,
which is a technical training institution for NASA.
2000, GA won a contract from the Federal Transit Administration’s
Low-Speed Urban Maglev Program to develop magnetic levitation technology
that would be cost-effective, reliable, and an environmentally
sound option for urban mass transportation. GA concluded that Inductrack
was the levitation approach that best met its needs, based on factors
such as simplicity, weight, capital and maintenance costs, and
design flexibility. Sam Gurol, General Atomics program manager,
notes that GA has worked with Livermore scientists, including Post,
for years on a variety of research projects, most of them related
to magnetic fusion.
at GA, Livermore, and other institutions have shown that a maglev
system using Inductrack offers many benefits, including its ability
to operate in all weather conditions and in terrain with steep
grades and tight turns, its low maintenance, and its rapid acceleration.
Also, its quiet operation allows elevated tracks to run through
neighborhoods, thereby eliminating the need to tunnel underground
for noise abatement. For many urban environments, the maglev system
can result in significant cost savings over conventional transportation
May 2003, General Atomics broke ground on a 120-meter-long
Inductrack test track, which will feature both straight and
Full-Scale Test Track under Construction
May 2003, GA broke ground at its San Diego facility on a 120-meter-long,
full-scale test track, which will feature both straight and curved
(50-meter radius) sections. In June, a test vehicle consisting
of a single, full-scale chassis unit (a mass transit vehicle has
two chassis units) was shipped to GA from Hall Industries in Pennsylvania.
The vehicle chassis is composed of upper and lower Halbach arrays,
additional Halbach magnet arrays for the propulsion system, auxiliary
wheels, and secondary suspension components.
test vehicle’s chassis is equipped with water tanks for varying
the weight during the test. The initial tests will be conducted
on the first 15 meters of the test track. Once the entire 120-meter
track is completed, the test vehicle will be operated (remotely)
at speeds sufficient for levitation.
purpose of the test track is to validate integrated levitation,
propulsion, and guidance,” says Gurol. “Each of these
has already been successfully demonstrated individually.” Upon
successful completion of trials, GA hopes to construct a demonstration
system at California University of Pennsylvania in California,
notes that the concept of magnetically levitated trains, based on
other technological approaches, has been studied in several nations
for decades. “Demonstration systems in Germany and Japan, while
impressive for the high speeds they attained, have proven to be both
technically complex and unusually demanding from an engineering standpoint.
What’s more, they have a high capital cost and are difficult
to maintain and to operate safely.”
For example, the Japanese
maglev system requires costly cryogenic equipment to cool its superconducting
coils and must accelerate to speeds exceeding 100 kilometers per
hour before it levitates. Also, passengers must be shielded from
the high magnetic fields generated by its superconductors. The German
maglev uses an electromagnetic design, which is based on magnetic
attraction rather than repulsion and requires control systems to
maintain a stable air gap of less than 10 millimeters. A breakdown
of the magnet control circuits or cryogenic systems could lead to
a sudden loss of levitation while the train is moving.
General Atomics’ full-scale
Inductrack test vehicle on the first section of the test
Drawing of the front end of urban
maglev vehicle showing the vehicle’s levitation/propulsion
module. Dual Halbach arrays of permanent magnets are positioned
under the train car to provide the levitating force.
Permanent Magnets Mean Fall-Safe Operation
the German and Japanese maglevs, no on-board power is required
to generate Inductrack’s levitating magnetic fields because
it uses permanent magnets. The permanent magnets also ensure
fail-safe operation. If the system were to lose power, the train
would remain stably levitated until it slows to walking speeds,
at which point it would settle down on auxiliary wheels. Also,
the use of permanent-magnet Halbach arrays allows a 2.5-centimeter
air gap between them and the levitated train car. Such a large
gap has advantages in foul weather and permits the construction
of tracks with looser tolerances.
says engineers rejected using permanent magnets for maglev systems
decades ago because the lifting forces developed by the magnets
were not powerful enough relative to their weight. That situation
was changed by two developments. First, the theoretical analyses
in the 1980s conducted by physicist Klaus Halbach of Lawrence Berkeley
National Laboratory resulted in his invention of the Halbach array.
Originally intended for use in particle accelerators for focusing
and controlling particle beams, the Halbach array is a special
configuration of permanent magnets. Each bar is at right angles
to adjacent bars so that magnetic field lines combine to produce
a strong field below the array and cancel out one another above
at about the same time as the Halbach arrays were conceived, permanent
magnets made of an alloy of neodymium, iron, and boron were developed
and put into large-scale production for such applications as computer
hard drives. Because they have a much higher magnetic field than
other permanent magnets, neodymium–iron–boron magnets
substantially enhanced the value of Halbach’s invention.
features a Halbach array of permanent magnets positioned under
a train car. The cars ride on a track of ladderlike construction
consisting of closely spaced “rungs” composed of tightly
packed bundles of insulated wire (litz wire). The conductors of
each rung are connected at both ends into a common bus bar, thereby
forming an array of shorted circuits. When the train starts to
move, the magnets induce electrical currents in the track’s
circuits. These currents produce a magnetic field that repels the
array, thus levitating the train car. This repulsive force lifts
the cars 2.5 centimeters or more above the track’s surface.
long as the train is moving above a few kilometers per hour, a
bit faster than walking speed, the car will be levitated by the
motion-induced currents and their resulting magnetic field. The
train will run on auxiliary wheels along rails until it reaches
the transition speed, at which point it will begin levitating.
If the power suddenly fails, the train cars remain levitated while
slowing down to a low speed, at which point the cars come to rest
on their wheels.
of General Atomics’ test track showing motor windings
embedded in the track. The windings are used with a linear
synchronous motor to power and brake the train. Train cars
ride on a track of ladderlike construction (suspension track)
consisting of closely spaced “rungs” composed of
tightly packed bundles of insulated wire (litz wire). When
the train starts to move, the magnets induce electrical currents
in the track’s circuits that produce a magnetic field.
This magnetic field repels the array, thus levitating the train
car 2.5 centimeters above the track.
Inductrack II Doubles Magnetic Field
the first Inductrack system was tested, Post introduced Inductrack
II, which features dual Halbach arrays straddling the track to
nearly double the magnetic field. Inductrack II, which is the design
used by the GA urban maglev system, requires half the current to
achieve the same levitation force per unit area as that required
when using the single-sided Inductrack I configuration, without
substantially increasing the weight or footprint area of the Halbach
arrays. Inductrack II thus has lower drag forces (higher levitation
efficiency) at low speeds than Inductrack I, an important asset
for an urban maglev system.
Inductrack, the train needs only a source of drive power to accelerate
it to levitating speed, keep it powered, and provide braking.
GA has selected an energy-efficient, linear synchronous motor
composed of a separate Halbach array underneath the train car
that interacts with motor windings embedded in the track.
by Post and Dmitri Ryutov at Livermore and colleagues at GA and
Carnegie Mellon University show Inductrack has an important advantage
over other maglev systems: Its performance can by analyzed theoretically
with a high degree of confidence. The theory has been compared
against subscale test results and then incorporated in simulation
codes. These codes can be used to design full-scale systems without
the need for expensive and time-consuming tests and modifications
as was the case for German and Japanese demonstration maglev systems.
analyses show that, if required by the application, Inductrack
systems can be designed to levitate more than 40 metric tons
per square meter of Halbach array, with up to 50-to-1 ratio of
levitated weight of a train car to magnet weight. These levitation
forces are close to the theoretical maximum that can be exerted
by permanent magnets. Actual values achieved in a test run at GA
are about 30 metric tons per square meter, in close agreement with
the theoretically predicted levitation force for the configuration
that was tested.
first commercial application is expected to be for an urban train
transport system. Other potential applications include intercity
high-speed trains, people movers, high-speed intercity shipment
of high-value freight in “pods” that would be levitated
in evacuated tubes, and maglev-assisted launching of rockets carrying
work on the demonstration effort proceeds in San Diego, the Livermore
team is optimizing the design of the magnets and the track. In
particular, the team is working on a novel laminated track composed
of a stack of slotted sheets of copper reinforced by fiber composite.
The new design is simpler and should be lower in cost to manufacture
than the litz-wire ladder track.
simpler, and cheaper than other designs, Inductrack increasingly
appears to be the right track to the future of urban transportation
Key Words: Halbach array, high-speed train, Inductrack,
magnetic levitation (maglev), permanent magnets, urban
For further information contact Dick Post (925) 422-9853
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