Relation between permanent magnet configuration and performance

The necessity for minimizing magnet weight has raised questions regarding the most efficient permanent-magnet shape for the magnetic circuit of air-borne magnetrons. The bowl-shaped permanent magnet was introduced, presumably because of its greater efficiency, to replace the conventional U-type permanent magnet.1 As far as is known, however, no direct evidence has been presented to support this view, and the purpose of this investigation was to determine by magnetic-circuit analysis the relative merits of the two permanent-magnet configurations.