Two-Stream Flow in Diodes

The stability of counterstreaming flow of electrons and ions in heavily biased diodes is investigated theoretically. Space-charge wave analysis is used to find the rf impedance function. The impedance function has first-order poles and zeroes. Nyquist analysis is used to see if any of them lie in the lower (unstable) half of the frequency plane. Some systems are stable for most passive terminations but can be made unstable for others. Other systems are absolutely unstable. The differences between instability induced by addition of passive circuit elements and absolute instability are discussed.