Observation of Low-Frequency Parasitic Oscillations in a 1.5 MW, 110 GHz Gyrotron

We report the observation of low-frequency parasitic oscillations, near 100 MHz, in a 1.5 MW, 110 GHz gyrotron operating in 3 microsecond pulses at MIT. The oscillations were measured on capacitive probes, which are located near the microwave resonator and are ordinarily used to measure the beam velocity pitch factor. The dependence of the frequency of oscillation on beam current, voltage, and magnetic compression ratio is discussed as are the regions of I-V space, in which the oscillations exist