Frequency Dependent Behavior of a Dynamo-Type HTS Flux Pump

The high-T c superconductor (HTS) dynamo is a type of superconducting flux pump that can inject a dc current into a superconducting magnet coil, without requiring physical connection to an external power supply. Here, we report experimental results from an HTS dynamo employing 46-mm wide coated conductor stator wire. We characterize the output of the device as a function of frequency, and show the effect of slitting the stator wire into two or three parallel equivalent strips. At operating frequencies above ~100 Hz, we observe that the internal resistance and open-circuit voltage ceases to increase linearly with frequency, and that the short-circuit current is greatly reduced. Experimental waveform data of the output open-circuit voltage enables us to identify three distinct and different signature waveforms, which mark the low-frequency, midfrequency, and high-frequency operating regimes. These regimes appear to arise due to the saturation of circulating currents within the stator wire, followed by a rise in temperature of the wire. We conclude that dissipation due to circulating currents plays an important role in depressing the output of this wide stator device at high frequencies. This effect is in marked contrast to results previously reported for a similar HTS dynamo employing narrower stator wires.