GB601966A - Improvements in or relating to electron discharge devices - Google Patents

Abstract

601,966. Thermionic valves ; electron multipliers. BULL, C. S. Oct. 24, 1944, No. 20673. [Class 39 (i)] An electron discharge device comprises a cathode 5, Fig. 1, control grid 6, screening or accelerating electrode 7, and electron collecting electrode 10, all these electrodes being surrounded by a substantially elliptical focussing electrode 13 ; the electrodes 5, 6, 7, 10 are disposed along the minor axis of the ellipse and do not extend beyond the limits thereof, and the device is operated so that electrons emitted from the cathode in divergent directions are caused to follow curved paths and to converge upon the collector 10. The focussing electrode 13 may be of sheet metal, or a mesh or wire-wound grid structure, or a series of rods ; when it is composed of a number of discrete parts gaps may be left between the parts provided the focussing field is not materially affected ; it is operated preferably at zero potential. Support rods for the electrodes 5, 6, 7, 10 may extend beyond the limits of the minor axis of the elliptical focussing electrode 13. In a modified construction the cathode 5 is emissive on one side only in which case the focussing electrode 13 is substantially semi-elliptical. The anode 10 may be secondary emissive, e.g. is coated with magnesium, a further collector electrode 11 of grid-like form being provided, as shown ; the electrodes 6, 7 may be wire-wound grids of elliptical form in cross-section. The cathode 5 and secondary emitter 10 need not be equally spaced from the centre of the minor axis of the elliptical electrode 13. A shield or shields may _be,disposed between the cathode 5 and secondary emitter 10 to shield the latter from material evaporated from the cathode, Figs. 3, 4, 5 (not shown), and the collector 11 may be of one or two flat or curved metal strips, Fig. 5 (not shown). If the anode 10 is not secondary emissive the electrode 11 is either omitted or used as a suppressor grid. Specification 545,803 is referred to. The Provisional Specification states in addition that the focusing electrode 13 may be operated at a negative potential and may be rectangular in shape.