Suspension and Guidance of Vehicles by Superconducting Magnets

Abstract

A magnetic suspension and guidance system for a very high-velocity (MACH 10) ground-based rocket sled facility has been studied.1 These results have been extended and applied to the study of a high speed (300 mph or greater) passenger train using this system. Suspension and guidance forces are obtained through the interaction of the magnetic field of an on-board superconducting magnet with eddy currents induced in a stationary metallic guideway. It was found that at high velocities the levitation force can be calculated as if the guideway had infinite conductivity. Thus, magnetic image methods can be used resulting in an image force FiFl=[μ0(ni)2πZ][2Z−(L2+Z2)1/2−(W2+Z2)1/2−(W2+Z2)1/2−(L2+W2+Z2)1/2W2+Z2(Z2)−(L2+Z2)1/2−(L2+W2+Z2)1/2L2+Z2(Z2)],where n is the number of turns, and i the current in a rectangular magnet of length 2l and width 2w at a suspension height z. At finite velocities, the resistivity of the guideway reduces the actual lift force Fl below Fi and produces a drag force Fd. Semiphenomenological expressions for these forces as a function of velocity and suspension height have been found for a magnet traversing a guideway of semi-infinite thickness and infinite lateral extent Fl/Fi=exp{−ζ[1+2(z/2l)3/2]−1}Fd/Fi=12(1−exp{−ζ[1+3(z/2l)5/2]−1])exp{−ζ[1+2(z/2l)3/2]−1},where ζ = (4π/μσvz)1/2, v is the velocity, and σ the conductivity of the guideway. Fl is approximately Fi when ζ < 1. These results are in semiquantitative agreement with experiments on normal magnets suspended over rotating metallic plates.2 Six superconducting magnets 0.5 m square, conducting 3×105 A - t are sufficient to levitate a 100-passenger vehicle weighing 60 000 pounds at velocities of 50–300 mph. These magnets would provide silent and smooth suspension and guidance, would require little maintenance, and would not require a high-precision guideway. The important results of this work are: (1) the lift force approaches Fi asymptotically; at speeds of ∼50 mph for magnets 0.5 m square, Fl≈0.8Fi. (2) The drag force at high speeds (>50 mph) decreases as v−1/2. (3) The suspension height is adjustable, 0.15 m seems reasonable. (4) Superconducting magnets of modest dimensions are practical and necessary for this application.