Patent GB-692697-A (GB)
Title: Improvements in electric discharge tubes embodying electron mirrors
IPC: H01J29/60
Filed: 1949-04-11
Abstract: 692,697. Cathode ray tubes. PHILIPS ELECTRICAL, Ltd. April 1). 1949 [April 14, 1948], No. 9769/49. Class 39(i) In a cathode-ray tube in which the beam is reflected by a mirror field produced by two or more electrodes 12, 13, Fig. 1, between which an oscillatory P.D. is applied to deflect the beam over output electrodes 10, 11, solid dielectric material is arranged between the mirror electrodes and the thickness or dielectric constant of the material vanes from point to point to give the oscillatory potential distribution between the mirror electrodes a desired form, preferably linear. The dielectric material preferably has a dielectric constant greater than four, e.g. titanium dioxide or porcelain. In one form, Fig. 4, a dielectric block 22 is arranged between and secured to the mirror electrodes 20, 21; it is thinner at the middle than at the ends. This gives a linear variation of instantaneous potential between electrodes 20, 21 when a high frequency voltage, i.e. one whose frequency exceeds 10<SP>15</SP> cycles per second, is applied across these electrodes via coils 18, 17, Fig. 1. In another form, Fig. 6, the mirror electrodes 25, 26 are plates arranged edge on to the beam and the dielectric block 28 has the shape shown; this again gives an approximately linear variation of potential. In a modification of this construction, Fig. 8 (not shown) the dielectric material is of even thickness but of varying dielectric constant across its width, and is coated on the side facing the cathode with a high ohmic resistance layer. The resistance layer is connected to one or both of, the mirror electrodes for high, and low frequency operation respectively. The dielectric material may be so distributed that the mirror field assists in focusing the electron beam, and to avoid distortion of the electrostatic field at the edges of the mirror electrodes. The prior art arrangement to which the invention may be applied has base plate 2, Fig. 1, with leads 3 to the gun and target electrodes and a location member 4; the mirror electrode leads are taken out via caps 15, 16 and receive a D.C. negative voltage via lead 19 connected to the mid-point of coil 17. The mirror electrodes are connected by a mica plate 14 which is coated with a high ohmic resistance layer, for example of colloidal graphite, in electrical connection with the mirror electrodes. The potential variation across the arrangement is undesirably non-linear. 692,699. High-frequency discharge apparatus. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. July 20, 1949 [July 21, 1948], No. 19159/49. Class 39(i). [Also in Group XL(b)] A velocity modulated electron discharge tube comprising an annular cathode surrounding a resonant cavity of toric shape, the walls of said cavity situated opposite said cathode being constituted by grids permitting the passage of the electron beam across said cavity, is characterized in that two annular focusing electrodes are arranged one each side of the cathode in such manner as to concentrate the electron beam towards the axial region of the torus, said beam being thus in the form of a solid of revolution whose thickness diminishes from the cathode towards the said axial region. In one arrangement, Fig. 1, an annular beam of electrons emitted by a cathode 1 is focused by electrodes 2 to pass across the grids 11<SP>1</SP> of a toroidal cavity resonator 3 in a converging path. Additional disc shaped focusing electrodes 7 and 7<SP>1</SP> which may be at the potential of the cavity resonator 3 are provided, together with an output coupling loop 5. The electrons are repelled towards the cathode 1 by the space charge effect alone, so that the arrangement provides a reflex velocity modulated tube having no reflector electrode. In a modified construction, the electrodes 7 and 7<SP>1</SP> are omitted and an auxiliary cavity resonator (see Group XL(b)) tuned to a frequency near that of the resonator 3 or to twice that frequency, is located in the region of the axis of the device to increase the bunching efficiency. An arrangement is possible wherein the electrons, instead of turning back to the cathode near the point where they were emitted, pass across the axis of the tube and through the grids of the resonator 3 on the diametrically opposite side, but the resulting very high space charge in the axial region would considerably disturb the electron stream at that point. This difficulty is overcome by the arrangement shown in Figs. 5a and 5b wherein an axial magnetic field set up by pole pieces N, S curves the paths of the electrons 6, 61 so that they no longer intersect on the axis. Tuning may be affected by varying the magnetic field to adjust the transit time of the electrons, and an auxiliary resonator 8 may be provided. In a further arrangement, Fig. 6, during the velocity modulation the beam 6 passes through grids 11 which are separate from the grids 11<SP>1</SP> where the electrons transfer their energy to the resonator 3. A deflector 4 corrects the paths of the electrons so that they cross the grids 11<SP>1</SP> at right angles.