Magnetic field inhomogeneity and torque in high temperature superconducting magnetic bearings
Matsumura, T.
Hanany, S.
Hull, J.R.
Johnson, B.
Jones, T.
Sch. of Phys. & Astron., Univ. of Minnesota, Twin Cities, MN, USA
This paper appears in: Applied Superconductivity, IEEE Transactions on Publication Date: June 2005
Volume: 15
,
Issue: 2
, Part 2
On page(s):
2316
- 2319
ISSN: 1051-8223
Digital Object Identifier: 10.1109/TASC.2005.849641
Current Version Published: 2005-06-13
Abstract
We give experimental evidence for the connection between magnetic field inhomogeneity of a permanent magnet and torque on the rotor in a high temperature superconducting bearing. Spin-down measurements below 14 Hz are used to demonstrate a high degree of correlation between variations in the angular speed of the rotor within a single period of rotation with the measured spatial structure of the magnetic field of the rotor. At frequencies below ∼1 Hz the fractional speed variation within a single period of rotation is inversely proportional to the square of the mean frequency of rotation. We propose that a dipole-dipole interaction gives rise to the torques that lead to speed variations and we show that this interaction explains the observed functional dependence on frequency. At frequencies above ∼1 Hz the measured magnitude is about 1% of the mean frequency of rotation, consistent with the noise level in the experiment. The results imply that arcminute accuracy angular encoding of the rotor can be achieved with a single measurement of angle in each period.
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