Patent GB-778854-A (GB)
Title: Improvements in or relating to low noise electron velocity modulation tubes
Inventor: BECK ARNOLD HUGH WILLIAM
IPC: H01J23/11
Filed: 1954-07-14
Abstract: 778,854. Space charge wave tubes. STANDARD TELEPHONES & CABLES, Ltd. July 14, 1954, No. 20554/54. Class 39(1). In a velocity modulated tube with buncher and catcher resonators, noise is reduced by means of a pre-buncher drift tube of critical length determined by the requirement that the buncher where the pre-buncher drift tube terminates shall be at a noise velocity minimum. and velocity jump amplification is provided in the main drift space, the device being such that in the absence of the velocity jump there would be power loss instead of gain ; the device may also utilise space jump amplification. In the preformed form, Fig. 6, the drift tubes 13, 5, 6, 7, 8, 9 are carried by disc seals and discs 22 together with metal rings 24, 25, 26 form the buncher and catcher resonators. There is one noise reducing velocity jump in the gun, i.e. between electrodes 13, 15 and two signal amplifying velocity jump stages in the main drift space the main drift tube electrodes being alternately at high and low potentials. Drift tube 7 has a larger diameter than the other drift tubes to give " space-jump " gain. The drift tubes, except 15, are an odd number of quarter plasma wavelengths long, the length of 6 and 8 being ¥#p and that of 13, 5, 7, 9, being <#p>/4, while the length of 15 is 0À6 #p so that a noise velocity maximum occurs 0À5 #p along it measuring from the jump where a similar velocity maximum obtains. Plates 20, 21 of magnetic material and forming pole-pieces for a focusing magnet (not shown) carry the gun and collector respectively, the gun comprising a cathode of sintered boriated nickel as described in Specification 750,339 focusing electrode 16, anode 12, spaced by insulators 17, 18, 19. In modifications there may be two stages of velocity jump amplification, each stage having also space jump amplification ; there may be an additional section or sections of pre-buncher drift tube. A mathematical discussion of reduction in noise due to (a) velocity fluctuations and (b) current fluctuations, in the beam is given and schematic forms discussed. In one such form, Fig. 4 (not shown) there is no velocity jump in the pre-buncher drift tube which is slightly longer than an odd number of quarter plasma wavelengths, the buncher being placed at a noise velocity minimum. Between the buncher and catcher resonators there is velocity jump gain possibly with additional space jump gain. In another such form, Fig. 5 (not shown) there is a velocity jump in the pre-buncher drift tube the drift tube section nearest the cathode having a length slightly greater than n<#p>/2 and the other section a length of an odd number of quarter plasma wavelengths so that the noise velocity is a minimum at the buncher. The tube is otherwise the same as in Fig. 4. It is shown that a velocity jump which reduces velocity noise increases current noise and it is stated that minimum total noise in the beam at the buncher is not dependent on such a velocity jump but depends only on the pre-buncher drift tube length which can be optimised. A prior art tube with velocity jump amplification and if desired additional space jump amplification is described with reference to Fig. 1 (not shown).