Design and performance of a high-efficiency laboratory electro-magnet

Major factors required in the performance of laboratory electro-magnets, namely field intensity and field homogeneity over accessible working volumes, have been achieved with moderate power consumption in an iron-clad magnet yielding power efficiencies [power efficiency ∝ (air-gap induction × air-gap)/ampere-turns] approximately 10% in excess of those obtained from similar magnets as previously reported. The magnet and support weighs 2½ t and operates from an 18 kW d.c. supply. Pole face diameters range from 11.5 to 1.5 in. with a range of air gaps from 5 to 0.5 in. Design procedure and data are reproduced.