72 Ë 3 Magnetic levitation
distribution for the PM Halbach arrays [65] used in Maglev may overcome this problem.
The PM Maglev systems of General Atomics and LaunchPoint Technologies use the PM
Halbach array technology.
In contrast to AMT and MagneMotion, LaunchPoint Technologies proposed the
concept of Personal Rapid Transit (PRT), which would employ a low-cost guide-
way with many small, low-speed vehicles to provide high passenger capacity [70].
LaunchPoint Technologies proposed a variety of guideway design ideas, depending
on the installation requirements. Guideways can be evacuated tubes (“Magtubes”)
or tubes open to the air. The Magtube system is flexible for both passengers and
freight.
Stable levitation forces and vertical forces are provided by stabilized permanent
magnet (SPM) technology [70]. For LaunchPoint Technologies, repulsors assembled
from PM Halbach arrays are used for levitation. Due to the special configuration of
repulsors, the system is stable vertically, but unstable laterally. Therefore, feedback
control is necessary to monitor and control the alignment of the repulsors with respect
to the rails. The vehicle magnets, the EM lateral stabilization, and the guideway
magnets together form the SPM levitation system. In fact, SPM is the control current in
the coil winding at the on-board Halbach arrays, thus, the stability is achieved. Lateral
stabilization keeps the vehicle centered with minimal power requirement (∼100 W/ton
of vehicle weight). High-strength NdFeB PMs arranged in opposing Halbach arrays
(see Fig. 3.2) provide levitation with a gap size of 30–80 mm at all speeds (no power
requirement for levitation). In order to reduce the cost of track, the magnetic field
of the track is weak. The magnetic field of on-board Halbach arrays is strong on
one side of the track, but weak on the other side, in order to ensure human safety.
A LSM propels the vehicle along the track. On-board motor coils interact with a
permanent magnet track to move the vehicle forward. The design speed of this system
is 800 km/h.
General Atomics reports an urban PM Maglev program [71]. Concepts developed
during the research on passive magnetic bearing systems at the Lawrence Livermore
National Laboratory gave a new approach to magnetic levitation, the Inductrack [72].
This Maglev system is unique in that operates with a large air gap of∼30 mm with
no feedback control required for stable levitation for the PM Maglev. Furthermore,
the packaging of the levitation magnets allows the vehicle to achieve a very tight
turn radius of 18.3 m [73]. The General Atomics Urban Maglev system can offer many
Fig. 3.2:Halbach arrays of LaunchPoint [70].