Spurious reflection of space charge waves in traveling wave structures

The high gain of traveling wave tube amplifiers makes them particularly sensitive to reflections at output ports and severs. Even small values of reflections can be significant if the reflected waves are regeneratively amplified. Consequently, a great deal of effort is expended in minimizing reflections. One process that complicates the design of devices is the additional reflection that occurs in the presence of the electron beam. The current procedure for minimizing reflections is based on the electrodynamic properties of the cold structure, i.e. in the absence of the electron beam. In the presence of the beam there is an additional reflection due to the beam space charge wave that is induced on the structure. Thus, structures optimized for zero reflection without the beam will have a reflection with the beam. The effect of the space charge wave is illustrated.