A major part of the bulk and mass of an extended interaction amplifier resides in its magnetic field source. Both can be considerably reduced by application of novel designs made possible by high‐energy product permanent magnet materials such as the samarium–cobalts and neodymium–iron–borides. We compare a structure derived from a hemispherical source design (‘‘magic igloo’’) with several more conventional permanent magnet and electromagnet configurations and find that mass reductions of 50% to 80% are often realized when the hemispherical source replaces any of the others. Such reductions afford considerable performance improvement in radars, radios, and jammers, especially in airborne and ballistic devices. Further compaction results from closer packing of field‐sensitive instruments afforded by leakage field reduction in the hemispherical source. Other advantages of the latter as well as drawbacks, are discussed.