High Rotational-Rate Rotor With High-Temperature Superconducting Bearings

We present results of an experiment with a 15.4-mm-dia, 150-mm-long rotor that uses HTS bearings for levitation and rotates in vacuum at kHz rates. Bearing losses are presented as a function of rotor speed up to a frequency of f = 1681 Hz. For f > 80 Hz (bearing resonances are at 28 and 41 Hz), the rotational drag increases monotonically with frequency up to a maximum at ~274 Hz, then decreases monotonically with frequency. For f >160 Hz, the rotational deceleration may be well represented by the term B + A(f/f₀)/[1+(f/f₀)²], where B and A are constants and f₀ is the frequency at the drag peak. The frequency dependent term may be interpreted as the circumferential inhomogeneity of the PM interacting with the flux-flow resistivity of the HTS. At higher speeds, the frequency-dependent term is governed by the skin depth and becomes proportional to 1/f^1/2.