Threshold Prediction of Spurious Oscillations in Klystrons Due to Backstreaming Electrons From Collector

In klystron amplifiers, spurious oscillations caused by the backstreaming electrons from collector may lead to unacceptable instabilities in experiments. To facilitate the fast and accurate analysis of such types of self-oscillations, rather than performing time-consuming particle-in-cell (PIC) simulations, the small signal theory to predict threshold conditions of spurious oscillations in klystrons has been further developed and implemented into the klystron computer code KlyC. If spurious oscillation occurs, the frequency and Q of the oscillation mode in a small signal regime can also be predicted. The effectiveness of the proposed threshold prediction method has been demonstrated through benchmarking against PIC codes, showing great agreement with result discrepancies at the several percentage level, while numerical computation time for small signal models is significantly (at least three orders of magnitude) faster than executed in the PIC simulations.