Asynchronous Magnet–Stator Topologies in a Squirrel-Cage Superconducting Dynamo

Abstract

For HTS dc magnet applications, a large proportion of the cooling load on the cryocooler is imposed by the external current leads. Removing the need for these current leads would allow these systems to be built using smaller, cheaper cryocoolers and reduce the ongoing operating costs. This can be achieved by using an HTS superconducting dynamo as a fully superconducting dc current source. Superconducting dynamos remove the need for external current leads by providing a wireless method of injecting dc current into a closed superconducting circuit. Most previous work on HTS dynamos has considered devices employing just one coated conductor stator tape, but dynamos employing multiple parallel stator tapes can achieve substantially higher output currents. In this study, we present an HTS dynamo design in which eight parallel HTS stator tapes are arranged in a cylindrical geometry, excited by an axially concentric rotor carrying multiple equally spaced Nd-Fe-B magnets. Here, we focus on the differing behavior observed between the synchronous case when the number of magnet nm is a factor of the stator number ns = 8 (i.e., nm = 1, 2, 4, 8) and the asynchronous case when it is not (i.e., nm = 3, 5). Our results indicate that both synchronous and asynchronous configurations can exhibit output short-circuit currents of up to ~1.3 kA. In both cases, a relative drop in performance is observed for higher values of nm. We find that the asynchronous magnet arrangement does not greatly improve the dynamo performance compared to the synchronous arrangement. At present, the thermal load associated with conduction-cooled current leads has prevented the practical realization of cryocooled HTS magnets in the kilo-amp (kA) range. However, the dynamo device reported here now offers a practically feasible route to novel kA-class portable cryocooled HTS magnet systems.