Patent GB-460356-A (GB)
Title: Improvements in and relating to electron discharge devices
IPC: H01J43/18
Filed: 1936-06-24
Abstract: 460,356. Discharge apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. June 24, 1936, No. 17586. Convention date, June 25, 1935. [Classes 39 (i) and 40 (v)] [Also in Group XXXVI] An electron multiplier has (a) a primary source emitting electrons which strike an emitter surface to liberate a larger number of secondary electrons, this operation being repeated to produce secondary electrons from surfaces at progressively increasing positive potentials, (b) a field electrode maintained at a uniform positive potential and producing a field normal to the emitter surfaces and (c) means for producing a magnetic field parallel to the emitter surfaces and transverse to the electron paths, the arrangement being such that when the potential on the field electrode is higher than that on any of the emitter surfaces, the field strength is the same at each surface ; preferably the field electrode is arranged closer to the emitter surface at the highest potential than to the surface at the lowest potential. As shown in Fig. 6, primary electrons from a concave photo-cathode 24 pass to a secondary emitting electrode 26 of high resistance, and the resulting secondary emission is collected by a cup-shaped anode 25. The field electrode 36 is mounted with one end nearer to the electrode 26 than the other, and may have a window for the passage of modulated light to the photo-cathode 24, and a curved part 37 to decrease charges on the envelope. A grid 35 of uniform mesh, connected with the cathode, may produce, with the field electrode 36 a variable mu effect in the accelerating field. An electromagnet 28 produces a transverse magnetic field. A screen grid (not shown), connected with the electrode 36, may be placed in front of the anode. The electrode 26 consists of a high resistance sheet or strip coated with secondary electron emitting material, and is connected with a potential divider 22 so that a difference of potential is maintained along it. The strip may consist of a thin film of nickel, molybdenum, or tungsten on a support of quartz, mica, porcelain, or glass known by the Registered Trade Mark " Pyrex ", or a glaze or enamel on a backing of metal connected through a condenser to earth. The coating may be caesium on oxidized silver. A molybdenum support may be sensitized with lithium borate by coating with a suspension of lithium borate in amylacetate, diethylcarbonate, or acetone containing a few drops of nitrocellulose ; barium peroxide may be used instead of lithium borate. Borates or silicates of barium or beryllium may also be used. In modification, Fig. 4 (not shown), the thickness of the metal plate is increased in steps, and the parts of the plate are connected separately with the potential divider. In another arrangement, Fig. 7 (not shown), the secondary emitting electrode consists of a number of plates of progressingly increasing width ; the plates may be mounted on an insulator or on an enamelled conducting plate. A potential divider, Fig. 9 (not shown), may be mounted in the envelope and consist of a coiled coil resistance wound with a varying pitch on a supporting rod. In a further arrangement, Fig. 11 (not shown), the secondary emitting electrode consists of a resistance strip and spaced plates. In the multiplier shown in Fig. 12, the secondary emitting plates 56 are mounted on an insulating tube 52, the photoelectrode 54 and the anode 55 consist of curved plates, and light is reflected by a curved plate 59 on to the photo-cathode 54. The field is produced by a cylinder 57 and a grid 58 formed of rods with progressively increasing pitch. Two coils, 51, producing a magnetic field, are mounted around the ends of the envelope. In the arrangement shown in Fig. 14, two beams from an indirectly-heated cathode 62 are focused by a grid 63 having side rods to which focusing plates 64 are attached, and secondary electrons pass along two rows of plates 65 to anodes 67, 69. The field electrode consists of a cylinder 68 of circular or other cross-section. The device may be used as a combined detector-oscillator and amplifier by connecting a tuned circuit 69<1> to one of the plates 65, the current oscillating by reason of the negative resistance through the plates, and an intermediate frequency being obtained in the output circuit 23. An input circuit 70 may be connected with the grid 63, or the grid may be kept at a constant potential, and the input applied to a winding between the two sections of the field winding 61. In the multiplier shown in Fig. 16, the secondary emitting plates 78 are mounted on each side of an insulating plate 77 which also carries the anode 79. The electrostatic field is produced by a curved plate 81 and a grid 82 formed of rods of varying pitch.