A new, all-electrostatic vidicon has been developed, in which crossed planar lenses are used to focus the electron beam sequentially in the frame and line directions, instead of the rotationally symmetrical lenses used in present-day electrostatic vidicons. The arrangement is the equivalent of crossed cylindrical lenses in light optics. Such planar lenses can be formed between two pairs of parallel plates. The second pair of plates of each lens is also used for scanning. By introducing a fine mesh in the plane of symmetry of a 2-element lens, one pair of plates may be omitted, thus increasing the focusing power of the lens and making it shorter. A computer program was written to plot electron trajectories. The computed results, together with experiments made on a scaled-up demountable gear and with sealed-off tubes, were used to optimise the design. In the course of the work, it was found that the image of a crossover, rather than that of a physical aperture in the electron gun, gave a focused spot more suitable for this particular application. The modulation depth of a 400 TV line pattern of black and white bars (i.e. 400 lines per picture height) is approximately 40% in the centre and 25% in the corners. Occasionally, over 50% modulation has been achieved in the centre. A remarkable feature is that the image field is practically flat. The geometrical fidelity is correct to within ±0.25% over the whole scanned area, is even better in the quality area in the centre, and is very uniform from one tube to another. This makes this type of tube highly suitable for the registration required in colour cameras.

New all-electrostatic vidicon

Publisher Summary This chapter analyzes the progress of the cathode ray tube during the past decade with special reference to its manufacture and design. The cathode ray tube, along with many other thermionic devices, has found extensive use in military operations—notably in radar. There has been considerable progress in developing methods of applying fluorescent powder to the screens of cathode ray tubes. Production of cathode ray tubes has not yet reached quantities at which automatic testing would be economic. The introduction of oscillograph tubes will probably mean that the all metal continuously pumped type will gradually become obsolete. A large fraction of the more academic wartime work on cathode ray tubes was directed to fluorescent screens and especially to afterglow screens. In practical post-acceleration tubes the after acceleration is gradual, with the result that there is some decrease in spot size but also some loss in deflection sensitivity. When high-beam voltages and high sensitivities are required, it forms a very convenient engineering method of achieving the appropriate features.

Cathode Ray Tube Progress in the Past Decade with Special Reference to Manufacture and Design

Properties of a simple type of emission system, such as is used in electron guns of cathode-ray tubes, have been investigated. It was found that the properties depend largely on the spacings between the electrodes of the system. For any grid-anode spacing, there exists a certain grid-cathode spacing referred to as the preference spacing, for which the current density in the focused beam is a maximum. The divergence of the emitted electron beam and the spherical aberration in it both have minimum values at this spacing, near which the crossover of the rays in the system occurs at a maximum distance from the cathode and in general the grid base is least. Some physical explanations of these effects are put forward. The presence of ions produced by traces of residual gas modifies the values of the preference spacings and tends to enhance the effects. From the results given it is seen that a direct application of first-order optical laws is not adequate to describe the crossover in an electron gun.

O. Klemperer

Papers

Electron Optics and Space Charge in Simple Emission Systems with Circular Symmetry