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A cathode-ray tube having a specially coated screen which changes color but does not necessarily luminesce when struck by the electron beam. It shows a dark trace on a bright back- ground.



Related Terms

SCREEN

The chemically coated inside surface of the large end of a cathode-ray tube which becomes luminous when struck by an electron beam.

TRACE

The luminous line resulting from the radial movement of the points of impingement of the electron stream on the face of the cathode-ray tube of a radar indicator. See also SWEEP.

CATHODE-RAY TUBE

A vacuum tube in which the instantaneous position of a sharply focused electron beam, deflected by means of electrostatic or electromagnetic fields, is indicated by a spot of light produced by impact of the electrons on a fluorescent screen at the end of the tube opposite the cathode. Used in radar displays.

AFTERGLOW

  1. The slowly decaying luminescence of the screen of the cathode-ray tube after excitation by an electron beam has ceased. 2. A broad, high arch of radiance or glow seen occasionally in the western sky above the highest clouds in deepening twilight, caused by the scattering effect of very fine particles of dust suspended in the upper atmosphere.

ANODE

  1. A positive electrode; the plate of a vacuum tube; the electrode of an electron tube through which a principal stream of electrons leaves the inter-electrode space. 2. The positive electrode of an electrochemical device, such as a primary or secondary cell, toward which the negative ions are drawn.

GUARD RING

  1. A ring-shaped auxiliary electrode surrounding one of the plates of a parallelplate capacitor to reduce edge effects. 2. A ring-shaped auxiliary electrode used in an electron tube or other device to modify the electric field or reduce insulator leakage; in a counter tube or ionization chamber a guard ring may also serve to define the sensitive volume. 3. A device used in heat flow experiments to ensure an even distribution of heat, consisting of a ring that surrounds the specimen and is made of a similar material.

BLANK

  1. To cut off the electron beam of a television picture tube, camera tube, or cathode-ray oscilloscope tube during the process of retrace by applying a rectangular pulse voltage to the grid or cathode during each retrace interval. Also known as beam blank. 2. The result of the final cutting operation on a natural crystal.

FLUOROSCOPE

A fluorescent screen designed for use with an x-ray tube to permit direct visual observation of x-ray shadow images of objects interposed between the x-ray tube and the screen.

CLEANUP

Gradual disappearance of gases from an electron tube during operation, due to absorption by getter material or the tube structure.

CUTOFF BIAS

The direct-current bias voltage that must be applied to the grid of an electron tube to stop the flow of anode current.

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