LOW ROTATIONAL DRAG IN HIGH-TEMPERATURE SUPERCONDUCTING BEARINGS

Bearings consisting of permanent magnets stably levitated over high-temperature superconductors exhibit low rotational drag and have the potential to enable high-efficiency flywheel energy storage. The coefficient of friction mu for such storage systems is derived as a function of bearing parameters and is shown to be an appropriate figure of merit to describe bearing losses. Analysis shows that values of mu < 10(-6) enables flywheels. A vacuum-chamber experimental apparatus has been constructed to measure values of mu for various experimental bearing designs. Experimental values for mu at low velocity have been as low as 3 x 10(-7) for an 89-mm-diameter ring permanent magnet stably levitated over an array of melt-textured Y-Ba-Cu-O. An important loss mechanism occurs from eddy currents induced in the rotating magnet due to the discrete nature of the superconductor array.