LOW ROTATIONAL DRAG IN HIGH-TEMPERATURE SUPERCONDUCTING BEARINGS

Bearings consisting of permanent magnets stably levitated over high-te mperature superconductors exhibit low rotational drag and have the pot ential to enable high-efficiency flywheel energy storage. The coeffici ent of friction mu for such storage systems is derived as a function o f 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 c onstructed to measure values of mu for various experimental bearing de signs. 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 levitate d over an array of melt-textured Y-Ba-Cu-O. An important loss mechanis m occurs from eddy currents induced in the rotating magnet due to the discrete nature of the superconductor array.