CUED Publications database

Origin of the DC output voltage from a high- T <inf>c</inf> superconducting dynamo

Mataira, RC and Ainslie, MD and Badcock, RA and Bumby, CW (2019) Origin of the DC output voltage from a high- T <inf>c</inf> superconducting dynamo. Applied Physics Letters, 114. ISSN 0003-6951

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Abstract

© 2019 Author(s). Despite their proven ability to output DC currents of >100 A, the physical mechanism which underpins the operation of a high-T c superconducting (HTS) dynamo is still debated widely. Here, we show that the experimentally observed open-circuit DC output voltage, V dc , is due to the action of overcritical eddy currents within the stator wire. We demonstrate close agreement between experimental results and numerical calculations, and show that large over-critical currents flow within the high-T c stator during certain parts of the dynamo cycle. These overcritical currents experience a non-linear local resistivity which alters the output voltage waveform obtained in the superconducting state. As a result, the full-cycle integral of this altered waveform outputs a non-zero time-averaged DC voltage. We further show that the only necessary requirement for a non-zero V dc output from any dynamo is that the stator must possess a non-linear local resistivity. Here, this is provided by the flux-flow regime of an HTS coated conductor wire, where conduction is described by the E-J power law. We also show that increased values of V dc can be obtained by employing stator wires which exhibit a strong in-field dependence of the critical current J c (B, θ). However, non-linear resistivity is the key requirement to realize a DC output, as linear magneto-resistance is not sufficient. Our results clarify this longstanding conundrum, and have direct implications for the optimization of future HTS dynamo devices.

Item Type: Article
Subjects: UNSPECIFIED
Divisions: Div C > Materials Engineering
Depositing User: Cron Job
Date Deposited: 09 Apr 2019 01:13
Last Modified: 13 Jun 2019 02:16
DOI: 10.1063/1.5085226