A series of periodically focused traveling-wave tube amplifiers

A series of traveling-wave amplifier tubes which employ lightweight permanent-magnet periodic focusing are described. These tubes have a combined frequency coverage from 1.0 to 11.0 kmc. The tubes employ parallel flow focusing of the electron beam and thereby avoid the complications of convergent flow magnetically-shielded electron gun construction. This type of focusing has the further advantage of using the same tubes as those where focusing is accomplished by solenoidal magnetic field. Control of the electron beam in the gun and the entrance conditions of the beam into the periodic helix field is accomplished by shaping of a magnetic field over the gun region.