Dynamo-type flux pumps provide a contact-free method of energizing currents in superconducting coils. Since a detailed predictive theory for these devices does not yet exist, the effect of design parameters must be studied empirically. In this work we investigate the performance of an experimental flux pump employing a high-temperature superconductor stator located upon a ring shaped iron yoke. The radial width of the yoke ring was varied and the DC output parameters of the device characterised at various operating frequencies and flux gaps. We observed that flux pump performance was relatively insensitive to the yoke ring width, for the range of values studied. A four-fold increase in ring width caused the open circuit output voltage and internal resistance to increase by less than 30% at the closest magnet-stator separation. The short circuit current was found to be almost entirely independent of the yoke width. Time-resolved output voltage waveforms were also obtained and related to the normal component of the magnetic field at the coated conductor stator wire, as calculated by finite element modelling. Our results imply that thin stator yokes can be utilized with little adverse impact on the electrical performance of these devices. Thin yokes reduce the total amount of iron required, and this is advantageous in terms of weight, cryogenic efficiency and eddy current losses.
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