The plasma-cathode electron gun

The development of a new type of plasma-cathode electron gun suitable for pulsed as well as CW operation with -beam lasers is reported. This device employs a plasma generated within a low-voltage hollow-cathode discharge rather than a thermionic emitter as the source of electrons. Electrons extracted from the plasma pass through a triode-type control grid structure and are accelerated to high energies in a plasma-free region prior to emerging from the gun through a thin foil window (the foil window was replaced by a solid collector in the tests described here). A plasma-cathode device producing a beam of up to 30 cm²in area has been evaluated at beam energies up to 140 keV, at 100-μs pulsed beam current densities up to 1 A/cm², and at CW current densities of greater than 0.7 mA/cm². The beam current uniformity has been evaluated and the beam has been measured to be monoenergetic to better than 3 percent at the foil-window location. The major life-limiting factors have been shown to be minimal. Devices capable of producing beams of arbitrarily large areas should he possible.