Numerical Determination of Vacuum Electronic Device Stability

We present a new approach to the study of the stability of vacuum electronic devices (VEDs) using the Naval Research Laboratory (NRL) large-signal code TESLA-Z. The approach combines a precomputed complex impedance matrix, $\hat {Z}$ , describing the structure with a TESLA-Z computed admittance matrix, $\hat {Y}_{ \boldsymbol {bt}}$ , characterizing the electron beam and beam tunnel. The gain matrix $\hat {G}$ for a given device then can be found as the product of the reduced $Z$ -matrix of the structure and admittance matrix $\hat {Y}_{ \boldsymbol {bt}}$ of the beam tunnel. Subsequent analysis of the eigenvalues of the gain matrix $\hat {G}$ using Nyquist’s method determines the stability of the device. We discuss the details of the new algorithm and illustrate its application to an experimental G-band serpentine TWT.