A superconducting suspension with variable restoring force and low damping

A technique for the magnetic suspension of small (< 1 mm diam) superconducting niobium spheres is described in which the restoring forces (shape of the applied field) can be conveniently adjusted and low losses in the translational modes of oscillation easily obtained. The suspension was developed for use in an experiment designed to detect the existence of fractional electric charge but is applicable to other experimental situtations as well. A typical sphere is suspended with a vertical period of oscillation of 1.5 sec and a Q of 3000. Adjustments can be made over the period range 0.6 to 9 sec and Q's as high as 8000 have been achieved.