Patent GB-723216-A (GB)
Title: Improvements in and relating to electron discharge devices
IPC: H01J31/04
Filed: 1951-07-20
Abstract: 723,216. Electron beam apparatus; electrode materials and processing. GABOR, D., and HART, T. G. July 15, 1952 [July 20, 1951; Dec. 20,' 1951], Nos. 17296/51 and 29922/51. Class 39 (1). An electron discharge device comprises means for directing an electron beam on to a reflector electrode comprising polycrystalline material having crystallites at and near the surface from which reflection takes place arranged in such a manner that a large proportion thereof have lattice planes parallel to one another and to the surface, means for varying the product of the velocity v of the electrons in the beam and the sine of the glancing angle # of the electrons with respect to the surface, and means for extracting electric energy from the electrons reflected from the reflector electrode. The invention utilizes the fact that with suitable materials the relationship between the reflection coefficient and the product v sin # is as shown in Fig. 2, due to the wave nature of the electron which causes interference phenomena; the maximum reflection coefficient may be at least 0.2 and as much as 0.8. In the embodiment shown in Fig. 3 electrons from a gun are accelerated to about 5 Kv and focussed to a parallel beam by electrodes 12 and 13; the reflector electrode 14 has a conical inner surface with a half angle of about 90 degrees. The ring shaped collector electrode 15 has an aperture at least equal to that of the end of the electrode 14 so that electrons which pass through electrode 14 without being reflected do not impinge on the collector electrode; the paths of reflected electrons are shown by the arrows in the Figure. The tube preferably operated by altering the angle # by altering the voltage applied between electrodes 12 and 13; it is also possible to keep # constant and vary v by altering the voltage across the tube. By working on the mid-point of the rising part of the curve 10, Fig. 2, the device may be used as an amplifier; working at the base of the curve the tube becomes a rectifier or a frequency-changer; working at the peak of the curve the tube may be used as a frequency-doubler. The tube may also be used as a voltage stabilizer since its output depends on the H.T. applied across it. In a modification, Fig. 8, the beam is in the shape of a narrow fan, the grid and first anode being provided with slits instead of circular apertures, and is passed between deflecting plates 33, 34 on to the reflecting electrode 14 and collecting electrode 15. The input is applied to the deflecting plates to vary the angle of incidence on the reflector electrode; the electrode 14 is preferably profiled in the form of a logarithmic spiral, but may be cylindrical or spherical. For use at high frequencies one of the deflecting electrodes may be a conductor of zig-zag shape mounted on a strip of insulating material or a conductor wound around a'flat slab of insulating material to form a flat helix; at still higher frequencies the deflecting electrode may be a metallic coating of a herring- bone pattern on an insulator of fixed silver as shown in Fig. 10, both the height of the undulations in the pattern and the spacing between the deflecting electrode being small compared with the wavelength. With these arrangements the deflecting voltage travels along the deflecting electrode at about the same velocity as the beam. Instead of a collecting electrode a helix or a demodulating gap may be used for extracting energy from the reflected electrons. The reflector electrode may be of graphite and may be prepared by cutting it with a tool having a rounded edge having a radius of curvature of a few thousandths of an inch. if the tool is advanced at a rate such that the cutting edge penetrates radially in each revolution by an amount just equal to the radius of curvature of the cutting edge the graphite is polished to produce the effect desired. According to the first Provisional Specification the graphite may be polished with cotton wool, and molybdenite is suggested as a possible alternative material.