High gain, high efficiency, TWT amplifiers

In this paper, results are presented from research carried out on the development of high efficiency, high power traveling wave tube amplifiers. A rippled wall traveling wave tube is sued as a slow wave structure for wave interactions with an 850 kV, 1 kA electron beam. an 100 kW signal from a magnetron is injected at the front end of the device and amplified by 15 - 30 dB giving an output power of 100 MW from a single stage amplifier. At higher gains the system tends to oscillate due to feedback from impedance mismatches at the structure ends. To overcome this the authors have used a severed amplifier consisting of two identical amplifiers in series and separated by an absorbing graphite section between the two amplifiers. With this device the authors have obtained 400 MW output power with an energy conversion efficiency of 48%. The authors shall present a comparison between the amplifier characteristics for the single and two stage amplifiers. Peak output powers are obtained in the severed amplifier at a beam current of 900 A, however, sidebands have developed and the output is no longer single frequency