Harmonic generation under small signal conditions in a traveling wave tube

In a klystron, charge overtaking of electrons leads to an infinity of AC current. The harmonic content therein can be calculated exactly, with or without space charge effects. This paper extends the klystron theory to a traveling wave tube (TWT). We assume that the electron motion is described by linear theory. The crowding of these linear orbits may lead to harmonic generation, as in a klystron. We calculate the buildup of harmonic content as a function of distance from the input, and compare these analytic results with the CHRISTINE code. Reasonable agreement was found. A dimensionless “bunching parameter” for TWT, X = √2Pin / (PbC), is identified, which characterizes the harmonic content in the AC current, where Pin is the power of the input signal, Pb is the DC beam power, and C is Pierce's gain parameter.