Mutual Inductance Measurement of the Superconducting Coil for the Joule Balance

The joule balance, an approach for precisely measuring the Planck constant at the National Institute of Metrology (NIM), China, is currently limited by the self-heating of the coil when the measuring current flows. To solve this heating problem, a superconducting coil has been built to replace the existing fixed coil wound with enameled copper wire. The movable coil set is formed by two enameled coils connected oppositely for easy alignment in air. However, the large self-inductance of the superconducting coil brings new challenges for the a mutual inductance measurement. Mutual inductance measurement of superconducting coil based on standard square wave compensation method is presented and discussed in this paper.