Modeling external circuit effects on MIG gun LFO behavior

Summary form only given. Low-frequency oscillations (LFOs) are sometimes observed in high average power gyrotrons, with a trapped electron population in the MIG gun region thought to drive the oscillation. While often times, the frequency and behavior of the oscillations correlate with the timing of electrons orbits trapped between the throat (magnetic mirror reflection) and the cathode (electrostatic reflection), this behavior is not universal. Furthermore, the initiation of the oscillations remains less clear, as the trapped particle trajectories are not easily accessed in a nominally operating gun. It is known that LFO behavior can change with changes to the power delivery circuitry, and so in new studies reported here, we augment our simulations with a newly created external circuit model (described in another paper at this conference). In general, the external circuit can be composed of simple R, L and C elements, and is attached to the anode and cathode where previously we had reflection free port boundaries. Specifically we look at the effect that the external circuit can have on establishing and modifying the frequencies of circulating electron populations, and we also look at transient phenomenon which might be involved in initiating electrons on trajectories susceptible to causing LFO´s.