Development of high power X-band TWTs

Summary form only given. A program to develop high-power X-band traveling wave tube amplifiers using relativistic electron beams (0.8-1.0 MV, 0.8-1.8 kA, 70-100 ns) is in progress. At output power levels in excess of 70 MW the development of asymmetric sidebands has been observed. Extensive analytical work suggests that this phenomenon is caused by the large energy spread that develops in the electron distribution during the interaction process. This energy spread excites a broad spectrum of noise as the modulated electron beam enters the second stage of the amplifier. Reflections from the ends of these structures cause only selected frequencies to be transmitted through the device, leading to the observed sidebands. To reduce the effect of reflections, and thus the development of sidebands, narrow passband structures with passband /spl sim/200 MHz are being used. These structures typically have group velocity /spl sim/0.01c. This value ensures that the feedback time from any reflections is comparable to the beam pulse duration. Measurements using these structures show gains over a narrow bandwidth with no evidence of sidebands.