ABSOLUTE INSTABILITY IN A TRAVELING-WAVE TUBE MODEL

A model is constructed to evaluate absolute instability which may lead to bandedge oscillations in a traveling wave tube. Under the assumpti ons (a) that all modes have forward group velocities, and (b) that the slow wave structure has a parabolic dispersion relation in the omega- k plane, the threshold coupling constant (Pierce's parameter C) is cal culated for the onset of absolute instability. The effect of distribut ed resistive loss in the circuit is included. The axial wave number an d the characteristic frequency of the oscillation at the onset are giv en. (C) 1998 American Institute of Physics. [S1070-664X(98)00512-6].