Realization of Bullard's disc dynamo

Abstract

We report experimental results from three successful runs of a Bullard-type homopolar disc dynamo. The set-up consisted of a copper disc with a radius of 30 cm and thickness of 3 cm which was placed co-axially beneath a flat, multi-arm spiral coil of the same size and connected to it electrically at the centre and along the circumference by sliding liquid-metal contacts. The magnetic field was measured using Hall probes which were fixed on the top face of the coil. We measured also the radial voltage drop across the coil. When the disc rotation rate reached Ω ≈ 7 Hz, the magnetic field increased steeply approaching B 0 ≈ 40 mT in the central part of the coil. This field was more than two orders of magnitude stronger than the background magnetic field. In the first two runs, the electromagnetic torque braking the disc in the dynamo regime exceeded the breakdown torque of the electric motor driving the disc. As a result, the motor stalled and the dynamo was interrupted. Stalling did not occur in the third run when the driving frequency was set higher and increased faster. We also propose an extended disc dynamo model which qualitatively reproduces the experimental results.

Fury: an experimental dynamo with anisotropic electrical conductivity

“…In recent years, a self-exciting dynamo with spiral arms was tested by Avalos-Zúñiga et al [31]. In 2018, the dynamo threshold was reached and the results presented at the MHD days meeting in Dresden (16-28 November 2018), more results have been provided to us in a private communication (Avalos-Zúñiga RA, 2022) and a manuscript on the dynamo results is now available in ArXiv [32]. This dynamo was designed according to the concept of Bullard's dynamo disc; however, it seems that an anisotropic conductivity would be a faithful model for this setup, too [33].…”

Analysis of Power Efficiency Produced by AC and DC Generators: A Literature Review

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