GB1350269A - Velocity-modulation tubes - Google Patents

Abstract

1350269 Velocity-modulated tubes VARIAN ASSOCIATES 19 April 1971 [15 April 1970] 27088/71 Heading H1D In a velocity-modulated tube-as described, a klystron or extended-interaction klystronthe beam of electrons projected from a gun to a collection passes in succession through a prebuncher resonant circuit, through a nextsucceeding floating buncher resonant circuit, and through output circuit means for excitation by the modulated beam, the drift tube interposed between the pre-buncher and floating buncher circuits providing a drift region corresponding to a reduced plasma angle # greater than 90 degrees, and preferably equal to 120 degrees, where wq is the reduced plasma frequency, Vo is the D.C. beam velocity, and I is the length of the drift space. It is shown that the space charge forces arising from the fundamental and second harmonic space charge waves reinforce one another in the vicinity of the centre of the electron bunches, but oppose one another in the inter-bunch regions, whereby the provision of an abnormally long drift space provides a period for continued drift of electrons towards the bunches before excessive degradation of the bunching within the bunches occurs. For the klystron shown, the pre-buncher cavity 5 is also the input cavity, and the reduced plasma angles corresponding to the drift lengths between the interaction gaps of cavities 5 and 11, 11 and 11<SP>1</SP>, and 11<SP>1</SP> and 13, are 120 degrees, 60 degrees, and 25 degrees, respectively. Alternatively, the prebuncher cavity 5 may be replaced by a plurality of cavities (e.g. 3, Fig. 7, not shown) to increase gain, the upstream one being the input cavity, the drift lengths between the cavities each corresponding to a reduced plasma angle of 60 degrees, and the different cavities being tuned to different fundamental frequencies in the vicinity of the pass-band of the tube, to broaden the latter. The velocity-modulated tube may alternatively be an extended-interaction klystron having single or cross-wound helix resonators.