Modeling of airgap influence on DC voltage generation in a dynamo-type flux pump

High-temperature superconducting (HTS) flux pumps are promising devices to maintain steady current mode in HTS magnets or to energize rotor windings in motors and generators in a contactless way. Among different types of flux pumps, the dynamo-type flux pump has been very common due to its simple structure and ease of maintenance. However, understanding the principle of dynamo-type flux pump has been challenging despite the recent progress. This article employs an efficient numerical model based on minimum electromagnetic entropy production method to analyze the performance of the flux pump in open-circuit mode. This model is much faster and efficient than previous works on flux pumps. In addition to the main behavior of the flux pump, this work investigates the influence of airgap and critical current density on open-circuit DC voltage of the flux pump. We compare the modeling results of open-circuit DC voltage for different airgaps to experimental ones obtained in (Bumby \textit{et al} 2016 \textit{Appl. Phys. Lett}. 108 122601), showing good agreement. Modelling results show that with increasing airgap, pumping voltage in the superconducting tape does not cease, but only reaches to insignificantly low values, which is not measurable via experiments. ... mehrIn addition, the voltage in open-circuit does not depend on the critical current density, as long as the superconducting tape is fully saturated with screening currents.