Compact Linear-Motor Type Flux Pumps With Different Wavelengths for High-Temperature Superconducting Magnets

To investigate the impact of applied magnetic field wavelength on the pumped current, compact linear-motor type high temperature superconducting (HTS) flux pump devices of two difference wavelengths were designed and built. These flux pumps are small in size, which generate DC-biased AC travelling magnetic waves, and charge DC current into HTS closed-loop in contactless manner. In this work, by comparing two applied wavelengths λ = 34.2 mm and 21.0 mm, we had experimentally investigated how the wavelength affects the pumped current in an insulated YBCO double pancake coil (DPC). From the experiments, it was found that, the wavelength has a significant impact on the pumped current, i.e., by shortening the wavelength of the applied AC travelling wave from 34.2 mm to 21.0 mm, the maximum pumped current increased accordingly, while the maximum increment of 53% had been observed. Meanwhile, the pumped current had increased to 65 A in the YBCO coil, which had almost reached the resistive region of the DPC. These results are helpful in optimizing the HTS flux pump devices, which might also be helpful to further understand the mechanism of flux pumps.