Simulations of the electromagnet system for the Joule Balance at NIM

The Joule Balance is one of the several promising methods for the precise measurement of the Planck constant h to redefine the kilogram. Compared with the Watt Balance, it benefits from its all static measurements. For the new generation of the Joule balance, a magnet system with high-permeability material is designed to reduce the problem of coil heating. Simulations are carried out to demonstrate the principle of the magnet system and optimize the design. Further analysis is made to improve the force profile by selecting proper lengths for the magnet coils. Results show that the flatness of the force profile could be achieved with several parts in 10^-5 when the coil moves from -50 mm to +50 mm.