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 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 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: 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: 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 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.

Abstract: The invention provides a glass enveloped thyratron having an anode carried by an anode pin extending through a glass neck in the thyratron envelope and forming a pant leg. The anode is surrounded by a screening box operated at cathode potential which has a back plate with a tubular portion extending away from the anode into the interior of said pant leg to surround said anode pin. The outer surface of the extremity of the pant leg is flared outwardly adjacent the back plate into engagement with a mounting collar secured to the rear of the back plate. The tubular portion of the back plate extends within the pant leg for a distance substantially greater than the extent to which the pant leg is enclosed by the mounting collar.

Abstract: A cooling arrangement which is primarily intended for incorporation in a high power variable capacitor consists of an elongate deflector mounted within an expandable tubular bellows. The movable end of the bellows carries one of two sets of capacitor vanes, and a fluid coolant is introduced into the other end of the bellows. The fluid is deflected by the deflector into the convolutions of the bellows wall to purge them of air which might otherwise be trapped. In this way the generation of localized hot spots is avoided.

Abstract: A co-axial magnetron in which in order to provide attenuation of slot resonances the axial coupling slots in the anode member are opened out at either end into round apertures into which resistive attenuating material is introduced in the form of discs having thicknesses corresponding to the thickness of the wall of the anode member. The discs are held in place by thin copper cylinders inside and outside of the anode wall member and overlapping the attenuating discs on either side.

Abstract: A segmented discharge tube device is provided, particularly for the discharge tube of a laser, in which a number of electrically isolated aluminium segments presenting a passage through which plasma may pass are located within an aluminium tube with heat conductive electrically insulating material in the form of anodization between the outer surfaces of the segments and the adjacent inner surfaces of the tube.

Abstract: A display arrangement is provided in the form of an elongate evacuated envelope (1) having a phosphor screen (11) which is capable of providing a very bright display. A number of mesh electrodes (6) are positioned side by side along the length of the envelope so as to selectively determine which portions of the phosphor screen emit light. By controlling the potential of the mesh electrodes, the display can be switched on and off rapidly to provide a versatile form of information display. A large number of evacuated envelopes can be assembled to form a two dimensional array and if desired a color display can be provided by using phosphor patched of different colors.