Simulation of Drive-Induced Oscillation in Coupled-Cavity TWTs

Drive-induced oscillation (DIO) is an instability that limits the achievable output power in wideband coupled-cavity traveling wave tubes (CC-TWTs). It occurs under large-signal conditions, when the electron beam is slowed as a result of its interaction with the circuit at the drive frequency. DIO occurs at a frequency very near the 2π point (band edge) of the lower branch of the cold circuit dispersion diagram. It is commonly accompanied by a sudden increase in the body current and a flattening of the power transfer curve at the drive frequency. The accurate prediction of the conditions for onset of DIO would be useful to the designers of CC-TWTs. In this paper, we present an approach to the prediction of DIO thresholds using the multifrequency large-signal simulation code TESLA-CC.