Vivek Kumar
L01, Dr. Steve Kenney and Dr. Whit Smith
Team Maglev
Technical Analysis of Halbach Arrays for use in Maglev Trains
Introduction
A magnetic levitation (Maglev) train is a type of railway transport which offers
advantages over existing electric and fuel powered trains in the form of higher speeds,
little friction except for aerodynamic drag, low energy consumption, as well as negligible
air and noise pollution [1]. There are two existent technologies of Maglev trains, ElectroMagnetic Suspension (EMS) and Electro-Dynamic Suspension (EDS), which use servocontrolled electromagnets and cryogenically cooled superconducting magnets,
respectively [2]. EMS and EDS technologies are used in German Trans Rapid and
Japanese Yamanashi trains respectively, operating at speeds of about 500 km/hr. A third
and newer technology uses Halbach arrays for levitation. Halbach arrays are a specific
arrangement of permanent magnets designed to produce a strong magnetic field on one of
their sides and a near zero magnetic field on the opposite side.
Commercial Applications of Halbach Arrays
Halbach arrays find applications in particle accelerators, free electron lasers as well as
Maglev trains where they are used to levitate the train and keep it at a distance from the
rail. Unlike the electromagnets or superconducting magnets used in EMS and EDS,
Halbach arrays do not require superconducting coils or stability control feedback circuits.
At the Lawrence Livermore National Laboratory, scientists have developed a new
Maglev technology using Halbach arrays. The technology, called Inductrack, is more
widely adaptable, simpler in design and operation and costs 40% less that electric trains.
Also, Inductrack is fail safe and in the event of a power failure, the train car would
simply slow down and settle on the rail with its auxiliary wheels. Having witnessed the
cost advantages of Inductrack largely because it does not require fuel, NASA awarded a
three year contract to the team to explore the idea of using Halbach arrays to launch
rockets into outer space [3].
Underlying Technology
Halbach arrays are designed to produce a strong magnetic field on only one of their
sides, thereby closely representing a monopole. The magnetic field near 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 [4]. Halbach arrays are mounted on
the underside of a train and run through its entire length. Magnetic fields are produced
from the moving Halbach arrays on the underneath of the train inducing a current in
close-packed shorted electrical coils mounted within the rail or track, levitating the train
and stably centering it between the two rails.
Building Blocks for Implementation
The arrays comprise smaller magnetic portions that are each magnetized differently to
produce magnetic fields in different directions [5]. Small portions are attached together to
form arrays in the shapes of cylinders, rings or cuboids for varying applications.
Numerous Halbach arrays can be attached together in series and this property is useful in
Maglev trains, often stretching up to a kilometer in length. Even though the
electromagnetic drag associated with Inductrack becomes small at high speeds, an
auxiliary power source would also be needed to maintain the train's high speed against
aerodynamic drag [6]. The amount of power needed depends on the weight of the vehicle
and its maximum speed. There are no software requirements for Maglev trains with
Halbach arrays because the use of electromagnetic forces allows the trains to levitate and
propel themselves.
References
[1] A. Heller, “A New Approach for Magnetically Levitation Trains – and Rockets,”
[Online Website], [cited 2009 Jan 20], Available HTTP: https://www.llnl.gov/str/Post
.html
[2] R. F. Post, Toward More Efficient Transport: The Inductrack Maglev System,
Lawrence Livermore National Laboratory, 2005.
[3] L. Tung, R. Post, and J. Martinez-Frias, Final Progress Report for the NASA
Inductrack Model Rocket Launcher at the Lawrence Livermore National Laboratory,
UCRL-ID-144455 (2001).
[4] C. Ham, W. Ko and Q. Han, “Analysis and optimization of a Maglev system based on
the Halbach magnet arrays,” Journal of Applied Physics, vol. 99, issue 8, 2006
[5] Adept, “Build a Halbach Array”, [Online Website], [cited 2009 Jan 21], Available
HTTP: http://www.matchrockets.com/ether/halbach.html
[6] Adept, “Halbach Arrays”, [Online Website], [cited 2009 Jan 21], Available HTTP:
http://www.gaussboys.com/pages.php?pageid=6