effect, the superconducting magnets behave like extremely powerful
and lightweight permanent magnets. As the vehicle moves, its magnets
induce currents in the guideway conductors, generating a magnetic
repulsive force that levitates the vehicle. The levitation is automatic
and inherent as long as the vehicle is moving, and is inherently
and passively stable. If the gap between the vehicle and the guideway
decreases, the levitation force on the vehicle increases, automatically
pushing it away from the guideway.
The simple conducting sheet guideway has a large magnetic drag
force because the induced currents in the guideway are comparable
to those in the superconducting magnets on the vehicle. While the
vehicle magnets are lossless, the induced currents in the normal
conductors on the guideway are not, and produce power losses, which
result in a magnetic drag force on the vehicle.
Realizing this, Powell and Danby focused on maglev designs that
minimize the magnitude of the induced currents in the guideway relative
to the superconducting currents in the vehicle magnets. This in
turn minimizes the losses in the guideway and the resultant magnetic
drag on the vehicle.
In their first maglev design, Danby and Powell proposed having
a sequence of simple conductor loops in the guideway, instead of
a conducting sheet. For a given magnetic levitation force, this
configuration has considerably lower power losses and magnetic drag
forces than the simple conducting sheet guideway.
Following their initial design, Powell and Danby then developed
even higher performance maglev configurations, as described in the
Learning to Levitate.