High-Temperature Superconducting Gradiometer Coupled With Large Pickup Coil Made of GdBCO Coated Conductor

We have fabricated a large high-temperature superconducting gradiometer for geophysical application such as a Transient Electro-Magnetic (TEM) method. The seamless gradiometric pickup coil was made of a commercially available GdBCO coated conductor formed on a Hastelloy tape. Two pickup loops with a diameter of 100 mm and an integrated input coil on a SQUID chip were connected with low resistance contacts. The input coil was magnetically coupled with a directly-coupled gradiometer which was made by a RE123-based multi-layer process including two superconducting layers with crossover, contact structure and ramp edge Josephson junctions. The baseline length defined as the distance of two pickup loops is about 130 mm. The performances of the gradiometer such as flux noise, gradiometer balance and frequency dependence of sensitivity were investigated.