Development of sidebands in ultra high power traveling wave tube amplifiers

Results are presented from recent research on the development of high-efficiency, high-power traveling-wave-tube amplifiers (TWTAs). A rippled wall TWTA is used as the slow-wave structure for wave interactions with an 850 keV, 1 kA, 100 ns duration electron beam. The output power of the tube is in excess of 400 MW at 8.76 GHz, corresponding to an electron beam to microwave energy conversion efficiency of 48%. At high output power levels (>100 MW), sidebands are observed to develop which carry an increasing fraction of the output signal as the beam current is increased. The sidebands are asymmetrically located with respect to the center frequency of the amplifier and do not appear to be associated with trapped particles. It is postulated that the sidebands result from finite length effects in the short amplifier sections used.<>