1. A device, within an electron tube or cathode-ray tube, that produces an electron beam and which directs its movement.
2. A device that directs a steady stream of electrons in a desired direction; for example, in a cathode-ray tube.

Electron guns are also used in oil refining and various other industries.

3. An electrode structure that produces and may control, focus, and deflect a beam of electrons; such as, in a television picture tube, 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 they are heated by a coil behind the support, these oxides produce electrons, that are drawn toward a positively charged sleeve (first anode) which 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

1. The ratio of the average amount of current density at a given opening to the average current density at the cathode surface.
2. A ratio of the average current density at any specified opening through which the electron stream passes to the average current density at the cathode surface.