Shaping of cylindrically symmetric magnetic fields with permanent magnets

With the increasing sophistication of electron-beam devices, there has arisen a need for more complex magnetic field profiles. Some novel permanent-magnet configurations are described which can provide cross-sectionally uniform magnetic field profiles with arbitrary field variation and almost no flux leakage to the environment. This is accomplished by an arrangement of axially and radially oriented magnets that achieve axial field modulation by variation of their geometrical dimensions, in one case, and of their magnetic properties, in another.