The Inductrack: A HomeGrown Maglev System for our Nation

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The Inductrack A Home-Grown Maglev System for
our Nation

• Lockheed Martin Palo Alto Colloquium
• Presented by Richard F. Post,
• Lawrence Livermore National Laboratory
• 15 Apr 2004

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There are many reasons why magnetically levitated
trains could be preferred over conventional trains

• Inter-city transportation Much higher speeds
  than are possible with steel-wheeled trains,
  lower noise, greater passenger comfort, increased
  safety against mechanical failures, reduced
  maintenance.
• Relative to aircraft Higher energy efficiency,
  safer, less weather-dependent, and
  would permit in-city departure and arrival.
• Urban transit systems Lower noise, much lower
  maintenance, greater rider comfort, can climb
  steeper grades, potentially higher energy
  efficiency than buses or rubber-tired urban
  trains.

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Two different types of Maglev trains have been
built and demonstrated at full scale at speeds up
to 500 km/hr

• Magnetic attraction - EMS (Electro-Magnetic
  Suspension) systems, using servo-controlled
  electromagnets on the train car, attracted upward
  to a iron-plate rail.
• Magnetic repulsion -EDS (Electro-Dynamic
  Suspension) systems, using cryogenically cooled
  superconducting magnets on the moving car,
  repelled by currents induced in coils embedded in
  tracks on each side of the train.
• Example EMS system The German Trans-Rapid TR08
  demonstration train and 30 kilometer test
  track, with operating speeds up to 450 km/hr.
• Example EDS system The Japanese Yamanashi
  demonstration train, with speeds of 500 km/hr on
  a 18 kilometer test track.

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The German Trans-Rapid maglev train is an EMS
system using electromagnets attracted to an iron
rail
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The German Trans-Rapid maglev train uses powered
electromagnets attracting upward to an iron rail
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The Japanese Yamanashi demonstration maglev train
uses superconducting magnets on its sides
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At speed superconducting magnet coils on the
Japanese train induce currents in coils in the
tracks on each side
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An EDS Urban Transit Maglev system test track
and test car has been built and operated in
Korea
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The proposed Swiss-Metro would link major Swiss
cities by maglev trains running in evacuated
tunnels.
Proposed in 1974, and under study since 1989, the
Swiss-Metro system would carry 200 passengers in
train cars running every 6 minutes. The trains
would operate in tunnels evacuated to 1/10
atmosphere (atmos. pressure at Concorde flying
altitude).
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The LLNL Inductrack maglev system developed as
a spin-off from the Labs flywheel energy storage
program

• It is an EDS system, but uses only permanent
  magnets and does not require cryogenically cooled
  superconducting coils
• It is a passive system that requires no control
  circuits to maintain stable levitation
• Levitation off of the auxiliary wheels occurs as
  soon as a low transition speed is reached.
• The Inductrack system isfail safe in the event
  of a power failure the train car would simply
  slow down and settle down on its auxiliary wheels
  at a low speed.
• The simplicity of the Inductrack should make it
  substantially less expensive than the present EDS
  or EMS maglev trains.

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LLNL Flywheel Technology and Applications

• Integrated System

Composite rotor
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The Inductrack system optimizes levitation
efficiency, using permanent magnets and a passive
track.

• Special arrays (Halbach arrays) of permanent
  magnets are employed, mounted on bogies
  underneath the car.
• The periodic magnetic fields from the magnet
  arrays on the moving train car induce currents in
  a close-packed array of shorted electrical coils
  in the track to produce levitation (above a low
  transition speed).

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In the 1980s Klaus Halbach came up with better
ways to employ permanent magnets in focusing
particle beams

• The Halbach array makes optimal use of
  permanent-magnet material by concentrating the
  field on the front face of the array, while
  nearly canceling the field on the back face of
  the array
• The magnetic field on the front face of the array
  varies sinusoidally with position parallel to the
  face of the array, and falls off exponentially
  with distance away from the front face.
• Only permanent-magnet material is employed in
  Halbach arrays no back ironelements or iron
  poles are needed.

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Klaus Halbach 1925-2000
Klaus Halbach, good friend and kind mentor, died
on 11 May 2000.
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Fields of the in-between permanent-magnet bars
add to the field of the adjacent bars below and
cancel above
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The moving Halbach array magnets induce currents
in the close-packed shorted circuits embedded in
the track
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One possible configuration of the Inductrack is
the magnetic equivalent of the flanged wheels on
a train
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The levitating force becomes effective at very
low vehicle speeds and remains constant at high
speeds
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The Lift-to-drag ratio of the Inductrack
increases linearly with speed, and can exceed 200
at maglev train speeds
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Our Inductrack model car is launched bypulses
from a series of electronic circuits
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The model Inductrack levitated and traveled down
its track in good agreement with the theoretical
design

• Front-view photograph of the cart and the track
  coil assembly. The cart is shown in flight
  approximately 3 centimeters above the track at
  approximately 10.5 m/s.

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Ferrite tiles add inductive loading for our
model Inductrack, reducing the transition speed.
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The Inductrack maglev concept may help NASA
reduce the cost of launching satellites

• NASA studies project that savings of 30 to 40
  percent of the rocket fuel, permitting
  single-stage-to-orbit missions, should be
  possible with maglev acceleration and launching
  up a sloping track at Mach 0.8.
• Under NASA sponsorship, we designed, built, and
  operated a model Inductrack system to demonstrate
  the concept, including a pulsed high-acceleration
  electromagnetic drive system.
• Preliminary estimates indicate that a full-scale
  Inductrack system for magnetically launching
  large rockets should be technically feasible.

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The cradle is fabricated from high-modulus
carbon-fiber composite to maximize rigidity and
minimize weight
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The levitated cradle surrounds the track that
is composed of levitation coils and interleaved
drive coils
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The NASA model track is made up of modules that
are composed of 13 interleaved drive and
levitation coils
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An analytical theory exists which can be used to
optimize the design parameters of an Inductrack
system

• Lift-to-Drag ratios can be specified by design
  over a wide range of parameters
• The ratio of levitated weight to magnet weight
  can be optimized for a given application
• Levitation forces approaching the theoretical
  maximum can be achieved in practical designs
• Economic factors, such as track conductor costs,
  can be analyzed and optimized
• Stability can be assured by the satisfaction of
  specific criteria (e.g., geometry, damping
  factors, etc.)

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The levitation and drag forces of the Inductrack
can be analyzed using circuit theory and
Maxwells equations
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To analyze the Inductrack we start with the
equations for the magnetic field components of a
Halbach array
Br Remanent field (Tesla), M no. of
magnets/wavelength. d(meters) thickness of
Halbach array magnets, k 2p/l
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Integrating Bx in y gives the flux linked by the
Inductrack circuits and yields equations for the
Lift and Drag forces
Newtons/circuit
Newtons/circuit
w width of Halbach array, L,R circuit
induct./resistance
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Dividing ltFy gt by ltFx gt yields an equation for
the Lift-to-Drag ratio as a function of the track
circuit parameters.
The Lift/Drag ratio increases linearly with
velocity, and with the L/R ratio of the
Inductrack track circuits.
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The levitation efficiency (Newtons/Watt) can be
determined directly from the equation for the
Lift/Drag ratio
Newtons/Watt
Typical K values K1.0 to 5.0, depending on
track design
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Design of the Levitation Track

• The track design must fulfill the need for
  efficient and cost-effective levitation coil
  circuits to take full advantage of the
  Inductrack maglev configuration.
• Two alternative track designs
• Litz-wire cables, encased in stainless
  steel tubes
• Slotted, laminated, conductor sheets,
  bonded and mechanically reinforced

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A ladder track can be constructed using
litz-wire cables encapsulated in thin-wall
stainless-steel tubes
Cable ends soldered Into shorting bus bars
The use of braided litz-wire in the cables
assures current uniformity and minimizes
parasitic eddy-current losses
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The laminated ladder track is a
high-efficiency, cost-effective, alternative to
the litz-wire ladder track
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The feasibility of the laminated track as an
alternative to the litz-wire ladder track is
under study at LLNL

• A computer code based on the Inductrack theory
  has been
• written to predict the lift and drag
  performance of the
• laminated track.
• ? An instrumented linear test track has been
  built
• to provide scalable data for comparison with
  the code
• and for use in the design of full-scale tracks.
• ? The LLNL code has been benchmarked against
  test-rig
• measurements for several Inductrack magnet
• configurations.

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Photo of LLNL Laminated-Track Test Rig
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There is good agreement between the LLNL code
predictions and the Inductrack test-rig
measurements
Track 15 laminations of 0.5 mm thick copper
sheet. Slots 15 cm. long, 0.25 mm. wide.
Conductor strips 2.5 mm wide.
The code predictions are shown for zero and plus
and minus 1.0 mm displacements
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The Laboratory is a member of a team that is
designing an urban maglev system employing the
Inductrack approach.

• The team (which also includes several engineering
  firms in the Pittsburgh, Penn. area), was
  organized by General Atomics (San Diego) and is
  funded by the Federal Transit Administration.
• The advantages of maglev in urban settings
  (relative to conventional urban rail systems)
  include Lower noise, lower maintenance, higher
  efficiency, higher grade and tighter turn
  capabilities (allowing operation on elevated
  tracks that can accommodate to an urban
  environment without the need for
  underground-tunnel operation).
• Better to satisfy urban (moderate speed)
  applications we have developed the Inductrack II
  configuration, which greatly reduces
  electromagnetic drag forces at urban speeds
  (relative to Inductrack I, which is more suitable
  for high-speed applications).

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The Inductrack II maglev employs dual Halbach
arrays, reducing drag losses and enhancing
levitation forces

• A cantilevered ladder track is used, interacting
  with two facing Halbach arrays, one above, and
  one below the track.
• The horizontal component of the magnetic fields
  from the upper and lower Halbach arrays are
  additive, while the vertical field of the lower
  array opposes that of the upper array.
• By adjusting the thickness or the width of the
  magnets of the lower array relative to the upper
  array an optimum level of induced levitating
  current can be achieved for a given levitated
  weight and magnet weight.
• Either a litz-cable flat track or slotted,
  laminated, sheet conductors with fiber composite
  reinforcement could be used to construct the
  cantilevered track.

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Adjusting the relative height of the Inductrack
II Halbach arrays optimizes the levitation force
vs drag power
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Inductrack II Lift-to-Drag Ratios
The L/D for Inductrack II systems is much
higher than for Inductrack I
Inductrack I
Inductrack II
Guideway parameters (both cases) 2.0 cm.
laminated copper, p.f. 0.9
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The General Atomics urban maglev system
employs The Inductrack II dual-Halbach-array
configuration
Vehicle on Guideway Linear Synchronous
Motor Suspension Track Double Sided Magnet
Array
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A full-scale levitation/propulsion test track is
nearing completion at General Atomics in San Diego
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Summary

• Magnetic levitation (maglev) trains have been
  under development for many years in Germany and
  Japan for high-speed rail systems.
• Maglev would offer many advantages as compared to
  conventional rail systems or inter-city air
  travel.
• The cost and complexity of presently developed
  high-speed maglev trains has slowed their
  deployment.
• The Inductrack maglev system, employing simple
  arrays of permanent magnets, may offer an
  economic alternative to existing maglev systems.
• The simplicity of the Inductrack may make it
  attractive for use in a variety of applications,
  including urban maglev systems, people movers,
  and point-to-point shipment of high-value freight
• The Inductrack, employing Halbach arrays, is an
  example of a practical application of the results
  of fundamental studies in magnetics and
  particle-accelerator physics.

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