A crossed-field gain mechanism employing discontinuities

Abstract

An extension of an earlier analysis by the author gives results which predict a gain enhancement in a crossed-field amplifier via discontinuities. The discontinuities are introduced into the slowwave structure as short drift-tube sections. The resultant gain is larger than could be obtained without the interspersed drift-tube sections, i.e., larger than would be obtained with an equivalent length slow-wave structure. It can be shown that the mechanism is neither a velocity jump nor a diocotron phenomenon. The discontinuity must be located where the three waves - attenuating, growing, and constant amplitude - are comparable in magnitude. If the discontinuity is introduced where the growing wave is dominant, the usual result is obtained, i.e., the growing wave just beyond the discontinuity suffers a loss when compared with its value immediately prior to the discontinuity. At the beam exit from the drift-tube region all three waves are excited even if the growing wave was dominant prior to the discontinuity. It is then possible to insert a series of alternating drift-tube discontinuities and slow-wave structures and utilize the gain mechanism. The discontinuities must be followed, ultimately, by a long slow-wave structure region where the growing wave will become dominant. If this is not done, the total circuit voltage, which is represented by the sumof the voltages at the circuit of the three waves, will be small and the advantages of boosting the growing wave are lost.