Study of the penetration of a 2 inches diameter YBCO thin film with the travelling magnetic wave

In this paper, we provide a thorough study on the penetration of a 2-in diameter YBCO thin film with the help of a travelling magnetic wave. The travelling magnetic wave is generated by a circular-type magnetic flux pump device, which is comprises of three phase windings and dc coils. We used one single hall sensor to measure the magnetic flux density 1.5 mm axially above the center of the sample. The results show that the presence of the YBCO sample had amplified the magnetic field by two times of the travelling wave in the center. After placing the hall sensor at r = 10 mm, we found that the magnetic field had been decreased by the presence of the sample. In order to clarify whether the flux had been bended or if there is an actual flux migration, we used a six-hall sensor array to measure the trapped field after applying the travelling wave. The measurement shows that the full penetration happens after the output voltage of the inverter V_ac ≥ 40 V (maximum field 4.4 mT). The results indicate that, compared with the standing wave, the travelling wave is more efficient to help vortices penetrate into the sample center. Moreover, in practical operation of a high-temperature superconducting (HTS) flux pump, an HTS film with large width is not recommended.