Electron-beam flow in superimposed periodic and uniform magnetic fields

Theoretical and experimental results are presented on the focusing of an electron beam by means of a magnet structure which produces, along the axis of the beam, a periodic magnetic field superimposed on a uniform field. The relation between space-charge and magnetic-field parameters for minimum ripple is derived. The flow in superimposed uniform and periodic magnetic fields is shown to be degraded from the flow of electrons in a magnetic field which has a sinusoidal variation along the axis. The results indicate the flow conditions to be expected, where such combined fields are unavoidable. The focusing of electron beams in this type of superimposed magnetic field and in Brillouin flow are compared.