Патент USA US2406824код для вставки
Sept. 3, 1946. 'J. H. FREMILIN - 2,406,824 ELECTRON DISCHARGE APPARATUS Filed June 25, 1941 Fig. 1; Ina/enter‘ ' Attorney Patented Sept. 3, 1946 2,406,824 ‘ UNITED STATES PATENT OFFICE 7 2,406,824 ELECTRON DISCHARGE APPARATUS John Heaver Fremlin, London, England, assignor to International Stan dard Electric Corporation, New York, N. Y. Application June 25, 1941, Serial No. 399,598 In Great Britain June 21, 1940 6 Claims. (Cl. 250-463) This invention relates to electron discharge ap paratus incorporating focussing systems for elec tron beams set up in the apparatus. It is common practice to provide, as focussing electrodes for an electron beam, tubular, aper- . tured-disc and other-shaped metal bodies at dif ferent points along the path of the beam such that desired beam converging ?elds and beam sibly equal to that of the conductor B. They then pass through the space within the grid wires in which the potential changes continuously. Finally they emerge into the equi-potential space within metal tube E. The potential gradient within the grid depends on the curvature of the wall of the outer conductor G and can be made of any desired form by suitably choosing this curvature. diverging ?elds may be set up mainly in the gaps In the ?gure the potential of the space within 10 between the bodies by the application of different metal tube E is made equal to that of the grid. potentials to the bodies. There is no reason, however, why the diameter Proposals have also been made, particularly and potential of DE should not have any desired with a view to obtaining continuous potential arbitrary value. In the same way the potential gradients along substantial lengths of the beam of the initial tubular portion B may be at any 15 path and thereby facilitating the concentration arbitrary potential. In some cases it is conven of beams of large intensity and density, to pro ient to have the diameter and potential of B vide interleaved conductors of different potential or E intermediate between those of the grid and in a common cylindrical surface, the conductors of the continuous external conductor, the grid at one- potential being tapered in one direction wires being then supported at both ends for 20 and the conductors of the other potential being example by thin sheets of mica. tapered in the opposite direction along the axis. From consideration of the conditions obtaining The present invention provides alternative structures providing greater freedom in design and simplicity in manufacture. in triodes it is known that when a grid at poten tial Vg is placed near to a plate at a different potential Vp then the grid will behave in some respects as though an effective potential V exist ed over the whole surface de?ned by the grid, The structure now proposed comprises a fo raminate tube or tubular grid surrounded by a co-axial tube capable of in?uencing the ?eld where V depends both on Vg and Vp, on the within the foraminate tube or tubular grid, one mechanical structure of the grid, 1. e. on wire or both of said tubular elements being of non 30 size and grid pitch and also on the distance uniform diameter along the length of the system apart of the grid and plate. The present in Preferably we employ a tubular grid of uni vention makes use of the property that the effec form diameter and a ?ared outer tube. The grid tive potential in a grid surface can be varied may be a wire helix or it may be constructed of continuously in any desired manner by suitably parallel wires in a cylindrical boundary. The shaping the outer relatively unbroken conductor outer tube is preferably of sheet metal although 35 and by suitably arranging the characteristics of it may be foraminate so long as the mesh is ?ne compared with that of the tubular grid. A focussing structure embodying the invention is shown in the accompanying drawing, Fig. 2 of which shows a section along the line A-A of Fig. 1. The structure shown comprises a tu— bular grid of parallel wires F extending from a metal tube E. Surrounding the tubular grid is the grid. Thus a convenient means is provided for the construction of certain types of electron gun. 40 Although in the figure the grid is shown as of uniform diameter, the outer conductor being ?ared, similar e?ects can be secured by using an outer tube of uniform diameter and a ?ared grid. Alternatively both elements may be of a sheet‘ metal tube G converging from a large 45 non-uniform diameter. diameter end adjacent the tube E to a cylindrical portion 13 of diameter comparable with the grid diameter at the free end of the grid wires F. A transverse insulating annulus C is provided for It will be clear that any desired potential dis tribution along the electron path can be set up by suitable grading of the tube diameters along the path, choice of grid aperture and of poten the mechanical support of the grid wires. 50 tials. The tubular grid with its tubular extension E In some cases it is desirable to arrange that and the outer sheet metal tube G are adapted the varying diameter changes in different senses to be maintained at di?erent potentials. at different points along the beam path. In It will be seen from the ?gure that initially cases where in the past three or more successive electrons coming from below as indicated by ar 55 tubular or apertured electrodes each requiring a rows H are moving in a space at a potential sen 2,406,824 different potential have been employed, equiva lent ?eld conditions can be now set up by the use of but two electrodes of different potential. The shape of the electrodes can be arranged so that speci?ed intermediate potentials appear at chosen points along the beam path. What is claimed is: 1. Electron discharge apparatus comprising, as a focussing system adapted When suitable poten of varying diameter along said coextensive part adapted when given a potential different from that of the foraminate tubular grid to modify the ?eld within said foraminate tube or tubular grid. 3. Electron discharge apparatus according to claim 2 wherein parallel wires in a cylindrical boundary serve as tubular grid and a flared sheet metal tube constitutes the outer co-axial tube. 4. Electron discharge apparatus according to tials are applied to provide a desired potential 10 claim 2 wherein the foraminate tubular grid has gradient along the path of an electron beam, a a sheet metal tubular extension at a ?ared end foraminate tubular electrode surrounded by a co of the outer ‘tube. axial tube capable of in?uencing the ?eld within 5. Electron discharge apparatus according to the foraminate tubular electrode, said electrode and tube being coextensive throughout at least 15 claim 2 wherein the outer tube converges upon and extends beyond one end of the foraminate part of their length and at least one of said tu tubular grid. bular elements being of non-uniform diameter 6. Electron discharge apparatus as claimed in along the coextensive length of the system. claim 2 comprising means for applying to the 2. Electron discharge apparatus comprising, as inner and outer tubes of the focussing system a focussing system adapted to provide a desired potential gradient along the path of an electron 20 potentials differing from each other and from that of a thermionic cathode disposed on the beam, a foraminate tubular grid of substantially axis of the focussing. system and co-operating uniform diameter a coaxial tube surrounding said with said system to form an electron gun. foraminate tubular grid and extending at least in part along the length of said grid and being 25 JOHN HEAVER FREMLIN.