Abstract: A magnetic thyratron interrupter is provided having between an anode and a cathode a structure having an aperture therein for a discharge presenting a succession of surfaces in the direction of discharge which are contacted when the discharge is moved by applying a magnetic field transversely to the discharge direction. Examples of structure are stacks of discs having concentric holes which are alternately of larger and smaller diameter and a strip of gauze wound into a spiral.

Abstract: A display arrangement utilizes a fluorescent screen 3 to provide readily alterable bright displays. The arrangement can provide a fairly large display surface, but can be of very small thickness. It contains electron emissive cathodes 5, and field electrodes 7 positioned closely adjacent to the cathode to control the emission of free electrons. Electrons which are freely emitted are accelerated to a mesh electrode 4 which is held at a modest positive voltage. A fluorescent screen 3 having a positive potential of several thousand volts is positioned closely in front of the mesh electrode. In preferred embodiments of the invention, a number of separate cathodes and/or separate field electrodes are provided, so that selected regions of the screen can be illuminated to provide desired display patterns. Individual regions of the screen can be switched on and off (i.e. rendered bright or dark) by the application of very low switching potentials to the field electrodes and/or the cathodes.

Abstract: A thyratron utilizable as a circuit interrupting protective device is provided. The thyratron includes an apertured grid between anode and cathode which is divided transversely into two parts separated by an insulating layer. Both surfaces of the composite grid remote from the insulating layer carry conductive meshes which meshes cover the exits of the apertures in the composite grid. The thickness of the insulating layer and the dimensions of the meshes are such that no point within an aperture is further from a part of the grid or a mesh than the Debye distance whereby the effects of Debye shielding tend to be reduced when a negative potential is applied between two said parts of said grid to quench a discharge previously initiated by applying positive potential to both parts of the grid.

Abstract: A millimeter coupled cavity travelling wave tube has each of its slow wave structures formed of at least one longitudinally extending member having holes made therethrough by a hobbing process, which holes constitute at least in part the cavities of the slow wave structure. In a preferred embodiment a one and one only such longitudinally extending member is provided, the holes therein each a whole cavity. The hobbing is such that a buttress is left outstanding from each cavity facing surface of a cavity separating wall and the beam hole is bored axially through said member from end to end through said buttresses. After machining of the cavity coupling holes in the cavity separating walls (e.g. by spark erosion) the cavities are closed by plates brazed to opposite faces of the member.

Abstract: A shielded faceplate for use in an image intensifier having a photocathode which comprises an inner core of glass transparent to light to which the photocathode is sensitive and an outer shielding region of glass which absorbs light to which the photocathode is sensitive. The outer shielding region surrounds and is adjacent to the inner core. The inner core has a transverse dimension which decreases along its length, the transverse dimension being smallest at the photocathode surface. The shielded faceplate is manufactured by arranging in a mold to which glass does not bond a first type of glass transparent to light to which the photocathode is sensitive and a second type of glass which absorbs light to which the photocathode is sensitive, heating the glass members so that they fuse to produce a block having an inner core of the first type of glass and an outer region of the second type of glass and removing the block from the mold.

Abstract: A millimeter coupled cavity travelling wave tube has its slow wave structures formed by a hobbing process. In a preferred construction, each slow wave structure is made of two individual halves each extending for the length of the structure. Each half contains one half of each cavity and one half of each beam hole and all of the portions of cavity and portions of beam hole in each half are formed in one hobbing operating. Coupling holes between cavities are formed where required by a process (e.g. spark erosion) separate from hobbing and if ferrules or drift tubes are required to extend out of the cavity separating walls in the finished tube, the beam coupling holes are made oversized and individual ferrules are brazed into position. The two halves of the slow wave structure are united by furnace brazing.

Abstract: The invention provides a linear beam tube which may be protected against high voltage arcs between the cathode and anode of its electron gun by connecting to ground a limiting impedance in a series path from said anode. The anode is carried upon the end of a ceramic cylinder which is co-axially within a conical metallic member. The end of the ceramic cylinder remote from the anode is attached to one end of said conical metallic member, the other end of which is flanged, with the flange passing through the tube envelope to provide an external termination which may be connected to ground. Resistive material is deposited in a groove in the inner surface of said ceramic cylinder to form a deposited impedance which extends from the anode over the end of the ceramic cylinder, to the end of the conical metallic member and constitutes said limiting impedance.

Abstract: A travelling wave tube has an output lead passing through a tubular output arm to a cap provided at the end of the arm. The cap has a cylindrical wall of ceramic material and is completed by a flanged plate of metal, to which said output lead is attached. When coupled to a waveguide, the travelling wave tube output arm enters an entry hole in one wall of the waveguide while the cap thereof abuts a matching ridge provided on the interior of the opposite wall of the waveguide. A small recess in the ridge locates the cap, the cylindrical wall of which acts as a window through which travelling wave tube output may pass into the interior of said waveguide.

Abstract: Thyratrons have an anode and cathode with a control grid lying between them. A primary grid located between the control grid and cathode may be used to maintain a primary discharge between it and the cathode, and improve the operating characteristics of the thyratron. However, the primary discharge may penetrate into the region where the main discharge occurs and hence increase the probability of premature triggering of the thyratron.By employing the invention, the penetration of the primary discharge into the main discharge region is reduced.A primary grid comprises two elements which have apertures. The elements are arranged so that the apertures in one element do not overlap those in the other. Thus the primary discharge which penetrates through the first element is prevented from reaching the main discharge region by the second element.

Abstract: Alternate polarity pulses of current are fed to a load L1A by charging a capacitor C5A alternately in different directions and closing unidirectional switches V2A and V3A at appropriate times to discharge the capacitor C5A through the inductor L1A. This arrangement is considered superior to an alternative system in which different capacitors are charged with different polarities to produce the different pulses. In the latter system the arrangement of switches needs to be such that the closing of one produces transient voltages which might cause the other switch to operate when it is not required to do so. In the illustrated system the switches V2A and V3A, being connected in parallel, do not suffer from this problem. In an alternative system the switches V2A and V3A could be replaced by a single bi-directional switch.

Abstract: A photocathode arrangement comprises a body of semiconductor material, such as gallium arsenide which is bonded to a fiber optic face plate. A thin anti-reflection coating of silicon nitride is positioned between the body and the plate and forms an integral part of the bond. The properties of the glasses from which the fiber optic face plate is made are carefully chosen to minimize crystal dislocations which can be introduced into the body of gallium arsenide when it is bonded to the face plate. Such crystal dislocations can seriously impair the performance of the photocathode. It has been found that it is advantageous to use a glass having an annealing temperature of about 575.degree. C. or less. Because of high temperature processing steps, its softening temperature must be about 680.degree. C. or greater. The photocathode arrangement so formed is intended to constitute the input port of an image intensifier.

Abstract: Conventional discharge tubes comprise electrodes within a separate containing vessel. The electrodes are joined to an external circuit by electrical conductors which pass through the vessel wall via an insulated side arm. Such a construction has disadvantages in that careful manufacture is required and it is also difficult to produce a desired distribution of the active medium in a laser and maintain a stable optimum temperature. In an attempt to reduce these problems the invention provides a discharge vessel which comprises electrical conductors and insulators arranged alternately so that a separate discharge vessel is not required. Since the discharge vessel is partially thermally conducting, temperature control is facilitated by its fast response to stabilizing controls, heat being supplied from an external source.

Abstract: A travelling wave tube arrangement is provided in which in order to support and cool the collector thereof the latter is cradled between two slabs of beryllium oxide attached to the walls of a channel in a block of copper, which walls are inclined in V-fashion. A further slab of beryllium oxide is provided above the collector. This last mentioned slab is attached to a flexible copper alloy wall which is dependent from a copper alloy plate which extends across the top of the channel. The plate is brazed to the block. A screw passing through the plate exerts pressure upon said flexible wall which in turn urges the beryllium oxide plate carried thereby towards the collector thus pressing the latter between the three beryllium oxide plates to form a electrically insulating support of good thermal conductivity.

Abstract: It is desirable to have a camera tube in which the signal plate has a low capacity. This may be achieved by taking a conductor from the signal plate through the glass faceplate. Previous methods of manufacturing a faceplate in which a conductor is embedded have proved unsatisfactory because of difficulty in carrying them out, and distortion and incomplete fusion of glass.A graphite mould having a base and walls contains and supports two glass blocks and a conductor and permits a degree of fluidity of the glass to be obtained which gives good fusion.

Abstract: The invention provides a laser arrangement including in its discharge circuit a switching thyratron which is capable of conduction normally in one direction and protectively in the reverse direction. The thyratron has an anode formed as a hollow body which is adapted to retain plasma generated during a pulse of forward conduction so that the anode is provided to act as a cathode permitting protective reversal of the thyratron when this is subject to reversal of voltage.

Abstract: A co-axial magnetron is provided with a cavity whose resonant frequency can be very rapidly altered in a cyclic manner so that the microwave output frequency of the magnetron can be chosen to lie within the available frequency band of the cavity. The cylindrical walls of the co-axial resonant cavity are constituted by or coupled to the inner surfaces of one or more tuning forks which are maintained in vibration by externally mounted electro-magnetic transducers. As the tines of the tuning forks vibrate, the effect is to cyclically increase and decrease the effective diameter of the cavity, thereby changing its resonant frequency. An adjustable end plate can be provided for the cavity so that fine tuning or slow rate tuning can be provided in addition to the frequency agility provided by the tuning fork.

Abstract: A photoconductive target camera tube provided to operate within a solenoid producing a uniform magnetic focusing field has a grid with a beam width defining aperture therein between the electron gun and the normally provided cylindrical anode. The aperture grid is mounted upon a ring of magnetic material which acts to reduce the magnitude of the focusing magnetic field at the plane of the aperture so to achieve a demagnification of the image of the aperture at the target with a consequent reduction in the beam spot size.

Abstract: The invention provides a laser arrangement including in its discharge circuit a switching thyratron which is capable of conduction normally in one direction and protectively in the reverse direction. The thyratron has an anode formed as a hollow body which is adapted to retain plasma generated during a pulse of forward conduction so that the anode is provided to act as a cathode permitting protective reversal of the thyratron when this is subject to reversal of voltage.

Abstract: A display arrangement consists of one or more elongate display devices, each of which has a number of separately energizable display areas positioned along its length. When energized, each display area is seen as a bright patch of light. As it is very difficult to arrange that the display areas extend right to the extreme ends of the device, optical deflection means are positioned in front of the display areas to magnify the size of each so that the total display area extends over the whole length of the elongate display device. The optical deflection means is arranged so that each bright patch is of substantially the same size. The invention enables a large number of similar elongate display devices to be placed end to end while avoiding the appearance of periodic dark patches at the ends of adjacent devices.

Abstract: A photosensitive tube of the kind having a photoconductive target formed of a material such as lead monoxide exhibits an effect generally termed lag when the tube operates at very low light levels. Lag is undesirable and can be minimized by providing a low light level bias which illuminates the rear of the target. The present invention provides light bias in the form of small light emitting diodes which are placed externally of the evacuated envelope of the tube in localized recesses adjacent to a tubular anode electrode at a point where the anode diameter changes. In this way the light emitting diodes can be accommodated within the normal overall envelope of the tube and in a manner which conveniently permits an even diffused illumination of the target. This arrangement is particularly applicable to small diameter tubes to which conventional light bias cannot readily be applied.