Mutual inductance measurement of the superconducting coil for Joule Balance

In the weighing phase of the Joule Balance, to get a high enough magnetic field and avoid the heating from the coil wound with normal enameled copper wire, a superconducting magnet is used as the fixed coil. The mutual inductance measurement between this superconducting coil and the movable coil of enamel copper wire should be measured precisely. A standard square-wave compensation method has been proposed to measure the mutual inductance. However, the 20H self-inductance of the superconducting coil is a big problem for the current source in the measurement. The technique for this special measurement is discussed here.