Vector-Potential Transformer With a Superconducting Secondary Coil and Superconducting Magnetic Shield

We created a complex coiled coil (vector-potential coil) to generate a curl-free vector potential. The device comprises a long flexible solenoid wound around a hollow nonmagnetic nonconducting cylinder; the entire coil has a coiled-coil structure. A straight superconducting BiSrCaCuO (BSCCO) wire was placed in the hollow cylinder at 77 K to serve as a secondary coil of a vector-potential transformer. We detected a nonmagnetic voltage induced between the ends of the secondary coil. The open-circuit voltage that was detected was the same as that of a normal conductor, i.e., a copper wire, which was also used as the secondary coil. Moreover, we replaced the hollow cylinder with a hollow superconducting BiPbSrCaCuO cylinder, which provides an ideal magnetic shielding. Even with the secondary coil inside the hollow BiPbSrCaCuO magnetic shield, the voltage induced across both BSCCO and copper secondary coils was identical to that measured when using the hollow nonmagnetic nonconducting cylinder.