| electron gun The part of a cathode-ray tube that emits a narrow beam of electrons, consisting of a cathode, control grids, and usually a heater. Electrons are emitted from the cathode, which is typically heated by electric current to give the electrons escape energy. The electrons are then focused into a beam by the electric fields of the control grids. |
stream of electrons (as from a betatron) generated by heat (thermionic emission), bombardment of charged atoms or particles (secondary electron emission), or strong electric fields (field emission). Electrons may be collimated by holes and slits, and, because they are electrically charged, they may be deflected, focused, and energized by electric and magnetic fields. Electron beams are used chiefly in research, technology, and medical therapy to produce X rays and images on television screens, oscilloscopes, and electron microscopes.
electrode structure that produces and may control, focus, and deflect a beam of electrons, as in a television picture tube (see ), where the beam produces a visual pattern on the tube's screen. The source of the electron beam is the cathode, a flat metal support covered with oxides of barium and strontium. When heated by a coil behind the support, these oxides emit electrons, which are drawn toward a positively charged sleeve (first anode) that is contoured to allow the electron beam to flow within the inside diameter. The beam is then electrostatically constricted and collimated by a metal disk with a hole (the control electrode) before it is directed to strike a phosphor-coated screen