Evaluation of equilibrium trajectory of superconducting magnetic levitation system for the future kg unit of mass

The superconducting magnetic levitation system for absolute determination of magnetic flux quantum /spl Phi//sub 0/, which is aimed at the future replacement of the kilogram unit of mass, has been developed at the National Research Laboratory of Metrology (NRLM) with a small floating body of approximately 25 g mass. The consistency of the relation between potential energy of the floating body and the electromagnetic energy of the superconducting magnetic levitation system has been evaluated with 1 ppm order resolution. In this paper, the results of the evaluation as well as the improvements made in the apparatus in recent years at NRLM are described.