Shielding Performance Evaluation of BIPM-Type Kibble Balance Magnet

How the background magnetic flux (far field) affects the magnetic field in a BIPM-type Kibble balance magnet is investigated. The field coupling paths along both the vertical and the horizontal directions are discussed based on finite element analysis. It is found that the vertical background coupling can contribute to the mean value of the radial field in the air gap while the horizontal background flux can only produce a weak torque in the weighing phase. The discussion helps to understand potential systematic errors in different realizations of Kibble balance measurements, especially for a magnet-moving balance.