Efforts to reduce CWI TWT noise and body current

Abstract

Summary form only given, as follows. RF output noise and body current levels are two very important performance characteristics of the Continuous Wave Illuminator (CWI) Traveling Wave Tube (TWT) during its manufacture and subsequent fleet usage. A high CWI TWT RF output noise level is typically caused by an ion-induced noise mechanism. Excessive body current is due to the beam radius being too large at axial locations near the collector end of the microwave/beam interaction region. The efforts described here include (1) a characterization of CWI TWT noise behavior, and (2) investigations of potential solutions to reduce CWI TWT noise and body current levels. CWI TWT noise behavior was characterized by capturing time-domain noise waveforms. The noise waveforms were captured with several tube operating parameters, such as cathode voltage, varied away from their nameplate values. Both amplitude and phase time-domain noise waveforms were collected. Operating the CWI TWT at significantly higher magnetic field values was investigated as a technique to improve body current performance. Use of a higher magnetic field reduces the body current because it tends to decrease the beam radius. Very high magnetic field values, however, cannot be used because they were found to decrease CWI TWT output power to an unacceptable level.