TYPES OF ELECTRON BEAM WELDING GUN
Diode (Cathode - anode) Gun: In this gun, the beam shaping electrode and the emitter are both at the same electrical potentials. These are, of simple construction but the only way to control beam current is by varying either the high voltage or filament temperature.
Triode (Cathode - grid - anode) Gun: The most widely used gun is the thermionic triode gun. The beam shaping grid can be biased to a slightly more negative value than the emitter in order to control beam current flow. In this case, the emitter alone is called cathode, focused with a spot diameter of less than 0.005 inches. Both of the gun types discussed above have directly heated filaments or cathodes, that is heated by passing an alternating or direct current (AC or DC) through it. Another method of cathode heating is indirect heating of these filaments by bombardment from another cathode known as the primary cathode.