GB708276A - Improvements in velocity modulation tubes of the kind comprising a drift space - Google Patents

Abstract

708,276. Velocity-modulated tubes. PHILIPS ELECTRICAL INDUSTRIES, Ltd. June 18, 1951 [June 21, 1950], No. 14373/51. Class 39(1) A velocity modulation tube comprising a drift space constituted by a conductive tube 3 of substantially circular cross-section, buncher and catcher gaps 6 and 7 respectively being formed between this tube and conductive tubes 4 and 5 and communicating with buncher and catcher resonant cavities 12 and 13, is characterized in that the drift space is provided with spaced radial or approximately radial extensions 15 which increase gradually in radial depth from about half way along the drift space, with the object of minimizing the loss which occurs owing to the diverging effect of the buncher gap on the electron beam flowing from the cathode 1 and concentration electrode 2 to the collecting electrode 14, which results in electrons impinging on the wall of the drift tube before reaching the catcher gap. Similar extensions 16 may be provided in the wall of tube 5 to reduce secondary emission from the end of this tube, and secondary emission is also reduced by bevelling the ends of tubes 3 and 5 at 17 and 18. The width of the extensions is at the most equal to the width of the catcher gap and the extensions occupy preferably not more than 75 per cent of the periphery of the drift tube. The extensions may be formed by conically milling the drift tube and then providing radial plates, or the extensions themselves may be milled out of the thickness of the tube wall. In a modified construction, for use if the wall of the drift tube is thin, the plates are soldered to the edges of longitudinal slots in the drift tube or alternatively one end of the drift tube may be formed by a peripheral series of members of U- shaped section arranged with their radial depth increasing gradually from about half way along the drift space. The U-shaped members may be interconnected at their outer edges by strips so that the drift tube has a toothed cross-section and electrons are prevented from entering the catcher resonant cavity. Alternatively, a drift tube of the latter form may be pressed out of a piece of sheet material.