Observation of Mode Competition in an 11.4-GHz Magnicon Amplifier

Summary form only given. We will describe the observation of a parasitic 8.05-GHz gyrotron mode in an 11.4-GHz frequencv-doubling magnicon amplifier experiment. The parasitic mode occurred only at high operating powers, when the beam transverse momentum was high, and caused a form of output pulse shortening. That is, tens or hundreds of nanoseconds after the magnicon mode turned on, the gyrotron mode would grow to high power, causing the amplitude of the magnicon mode to fall off. We will compare the behavior of the magnicon and gyrotron modes to the predictions of time-dependent multimode simulations.