Patent GB-450138-A (GB)
Title: Electron multiplying device
IPC: H01J29/02
Filed: 1934-10-05
Abstract: 450,138. Photo electric cells. TELEVISION LABORATORIES, Ltd., 505, Crocker Building, San Francisco, U.S.A. Oct. 5, 1934, No. 28548. Convention date, Oct. 7, 1933. [Class 39 (i)] A method of amplifying an electron flow consists in directing the flow against a surface at a velocity sufficient to produce secondary emission by impact, accelerating the secondary electrons to a like velocity to produce secondary emission from a similar surface, repeating such impacts between the two surfaces until the desired amplification is reached, and collecting the resultant electrons at an electrode disposed between the surfaces ; the source of primary electrons is preferably photo-electric and apparatus employing the method may be used as a television image dissector. In the image dissector shown in Fig. 2, the secondary emitting electrodes 26, 27 consist of two plates of nickel with or without a coating of caesium, and the collecting electrode or anode 29 consists of a cylinder mounted between the plates. A tube 30, preferably integral with the anode 29, carries the lead for the plate 26. A screen 26<1> of fine mesh, adapted to emit secondary electrons, is mounted in an aperture in the plate 26 facing the scanning aperture 25 in an anode 24 on to which electrons from a photo-electric cathode 22 are focused by a winding 32 energized by continuous current, and deflected by coils 34, 35. The winding 32 also guides the secondary electrons between the plates 26, 27 and away from the anode 29, the electrons being alternately accelerated and retarded by the potential differences between the anode 29 and the plates 26, 27. The secondary 37 of a transformer, supplied from an oscillator 40 at a frequency of 50 megacycles, is connected with the plates 26, 27. A switch 49 is connected across the secondary 37, and the centre of the secondary is connected through an output resistance 41 and a supply of potential 44 with the anode 29. A generator 46 of oscillations at a frequency of one megacycle, is connected in this circuit, and may be short circuited by a switch 47. When the switches 49, 47 are open, a high frequency potential is superposed on the anode potential, and secondary electrons pass to and fro between the plates 26, 27 before being collected by the anode, the output current being prevented from building up to a maximum equilibrium value. The duration of the half period of the oscillating potential between the plates 26, 27 is of the same order as the time of transit of an electron between the plates. When the switch 47 is closed, and with a weaker magnetic field, the radial field between the plates 26, 27 and the anode 29, aided by the space charge, produces a drift of secondary electrons towards the anode, successive imparts of electrons occurring closer to the periphery of the plate 26, 27. Reference is also made to a method of operating a device containing gas. In a modification, Fig. 3, (not shown), the tube containing the lead for the plate 26 is mounted near the centre of the anode and is negatively biassed so as to set up a transverse field producing a drift of secondary electrons towards the anode, the oscillator 46 being dispensed with. The Specification as open to inspection under Sect. 91, comprises also the image dissector shown in Fig. 5 (Cancelled) in which the amplification is by gas ionization. The anode 24<1> of the scanning device forms part of a metal container 60 enclosing the multiplying device which has a lining 61 of metal gauze spaced by glass beads from the container, and with a part 65 of heavier mesh coated with caesium. The amplifier anode consists of a filamentary ring 66 insulated by beads from a tube 70 projecting from the container. The anode 66 is connected through an output resistance 71 with a positive potential, the container is connected to earth, and the lining 61 is at a few volts positive. Secondary electrons from the part 65 pass to and fro through the anode 66 and ionize the gas. Positive ions pass through the lining 61 to the container and any secondary electrons emitted by the container are collected by the lining. Electrons liberated by collision with gas molecules traverse the chamber successively through smaller orbits and are collected by the anode 66. This subjectmatter does not appear in the Specification as accepted.