Magnetic field inhomogeneity and torque in high temperature superconducting magnetic bearings

Tomotake Matsumura, Shaul Hanany, John R. Hull, Bradley Johnson, Terry J Jones

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)2316-2319
Number of pages4
JournalIEEE Transactions on Applied Superconductivity
Volume15
Issue number2 PART II
DOIs
StatePublished - Jun 1 2005

Keywords

  • Polarimeter for observational cosmology
  • Superconducting magnetic bearing

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