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15 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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Vivek Kumar

L01, Dr. Steve Kenney and Dr. Whit Smith

Team Maglev

Technical Analysis of
Halbach Arrays
for use in Maglev T
rains


I
ntroduction




A

m
agnetic levitation

(Maglev)

train
is

a type of railway transport which
offers

advantages over existing ele
ctric 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, Electro
-
Magnetic Suspe
nsion (EMS) and Electro
-
Dynamic Suspension (EDS), which use servo
-
controlled electromagnets and cryogenically cooled superconducting magnets,
respectively [2]. EMS and EDS technologies are used in German Trans Rapid and
Japanese Yamanashi trains respective
ly, 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
side
s

and a near zero ma
gnetic 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 distanc
e 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 a
rrays to launch
rockets into outer space [3].




Underlying Technology


Halbach arrays are designed to produce a strong magnetic field on only one
of their
side
s
, thereby closely representing a monopole.
The magnetic field near the front face of
the a
rray 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.
M
agnetic fields are
produced
from the moving
Halbach arrays on the underneath of the train
inducing
a
current
in
close
-
packed shorted electrical coils

mounted with
in the rail or track, levitatin
g

the train

and stabl
y

centering it between the two rails.



Building Blocks for I
mplementation


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 f
or 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 Magl
ev train
s with
Halbach arrays because

the use of electromagnetic forces allows the train
s

to levita
te 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

.htm
l

[
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 t
he 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.gaus
sboys.com/pages.php?pageid=6