Observing and Suppressing an RF Noise Excited by a Parasitic Oscillation in a Collector of 170GHz-gyrotron

An rf noise of about 570 MHz was detected with a pick-up coil in an operation of 170GHz-gyrotron. Experiments and calculations indicated that a parasitic oscillation in the collector excited the rf noise at a resonance of TE1,(1,2) mode. The rf noise was successfully suppressed by increasing the retarding voltage or attaching a thin iron plate which asymmetrically covered the bottom of collector.