VELOCITY DEPENDENCE OF ROTATIONAL LOSS IN EVERSHED-TYPE SUPERCONDUCTING BEARINGS

Results of free spin down in vacuum are reported for an Evershed-type superconducting bearing in which a permanent magnet (PM) ring is levit ated over an array of high-temperature superconductors (HTSs) and unde r a similar PM ring in magnetic attraction. The velocity dependence of the rotational loss strongly suggests that the observed velocity-depe ndent losses are primarily due to eddy currents induced in the PM by i nhomogeneity of the field produced by the magnetized HTS array. The re sults show that the Evershed-type bearing is capable of reducing these eddy-current losses to an extremely low level, so that at a maximum m agnet rim velocity of 28 m/s, the fractional kinetic-energy loss per h our was 2.4 x 10(-4). Significant levitation heights are also possible , and at a 23 mm height, we measured a low-speed coefficient of fricti on of 3 x 10(-8). (C) 1997 American Institute of Physics.