GB469477A - Improvements in or relating to electron discharge devices - Google Patents

Abstract

469,477. Electron multipliers. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Jan. 27, 1936, No. 2586. Convention date, Jan. 30, 1935. [Classes 39 (i) and 40 (v)] A multiplier comprises a positively-biassed target electrode, an output electrode positively biassed with respect to the target, a " withdrawing " electrode also positively biassed with respect to the target and opposite to it and a cathode, and a magnetic field is set up parallel to the target surface. In one form, Fig. 2, an indirectly-heated cathode is surrounded by a cylindrical grid 51 having an apertured end 53 with a gauze 55, a set of multiplying target electrodes 3, and an oppositely-disposed set of withdrawing electrodes 5, each mounted on a mica sheet 7, and an output electrode 19. A magnetic field parallel to the target electrodes and perpendicular to the axis of the tube is set up by a pair of plates outside the tube joined by a U-shaped member on which is wound an energizing coil, or by a permanent magnet or solenoid. The electrodes are biassed by tappings on a potentiometer, the first withdrawing electrode 5 being at a higher potential than the last target 3. In a modification, the thermionic cathode is dispensed with and an additional electrode 3 serves as a photo-electric cathode. The withdrawing electrodes may be of molybdenum, tantalum, or nickel and the targets of silver. Discharges are passed between each pair of electrodes 3, 5 in oxygen at 1 mm. until the targets are oxidized to a bluish-green colour. Caesium, sodium, rubidium or potassium is distilled in after pumping, and the tube is heated for ten minutes at 210‹ C. Excess alkali metal may be taken up by a lead oxide getter. In another modification, the sets of targets and withdrawing electrodes may be combined into single resistive films formed, for example, by sputtering metal on to mica, and a potential gradient may be maintained along them. For generating oscillations, a tuned circuit may be connected in any target lead, so that the device acts as a dynatron, succeeding stages amplifying the oscillations. The input and output circuits of the tube shown in Fig. 2, may instead be coupled together for a generator or the tube may serve as a detector. Modulation may be applied to the lead to any target which is oscillating.