Electron Gun

Electron gun is the heart of various electron devices. These include television tubes, oscilloscope tubes, electron microscopes, and X-ray machines. In a television tube, an electron gun produces a pencil-sharp electron beam, which is accelerated toward the phosphorescent screen. The electrons strike the phosphor in the screen, causing it to glow. The beam "writes" the picture on the screen in much the same way that a pencil writes on paper. The higher the electron velocity, the brighter the image on the screen. In television receivers, the gun writes several hundred horizontal lines for each picture. It writes each line in a sixty-millionth of a second.

An electron gun has several basic parts. A cathode is the source of the electrons. These electrons are "boiled out" of the cathode at a high temperature and accelerated toward an anode some distance away. A control grid next to the cathode modulates (controls) the intensity of the electron stream. Beyond the control grid, an electron lens focuses the highly accelerated electrons into a tiny spot. A deflection system can be used to move the focused beam spot across a phosphorescent screen or other target.

Contributor: James E. Thompson, Ph.D., Prof. and Chairman, Department of Electric Engineering, Univ. of Texas, Arlington.

Electron Gun

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