High-speed magnetic rotor with HTS bearings for precision energy losses investigation

The authors investigated physical mechanisms for flux pinning and energy losses due to inter- and intragrain flux motion by a high-accuracy experimental technique that uses the levitation effect. Low-power self-stabilizing magnetic rotors with HTS bearings have been designed on the basis of the obtained results, with rotational speeds up to 200,000 RPM. The low energy consumption of the rotor enabled the determination of the energy losses in any sample in alternating magnetic field with an accuracy down to 10/sup -11/ W. By this method, the authors investigated magnetic flux dynamics in Y-123 and Bi-2223 granular superconducting samples and determined that flux motion in a Y-123 sample is described by intragranular thermally assisted flux flow with viscosity equal 8/spl middot/10/sup -5/ kg/m/spl middot/sec. They have also studied the frequency dependencies of energy losses for rotors with nonideal magnetic symmetry and found optimization criteria for rotor design.