Development of plasma cathode electron guns

The status of experimental research and ongoing development of plasma catho de electron guns in recent years is reviewed, including some novel upgrades and applications to various technological fields. The attractiveness of th is kind of e-gun is due to its capability of creating high current, broad o r focused beams, both in pulsed and steady-state modes of operation. An imp ortant characteristic of the plasma cathode electron gun is the absence of a thermionic cathode, a feature which leads to long lifetime and reliable o peration even in the presence of aggressive background gas media and at for e-vacuum gas pressure ranges such as achieved by mechanical pumps. Dependin g on the required beam parameters, different kinds of plasma discharge syst ems can be used in plasma cathode electron guns, such as vacuum arcs, const ricted gaseous arcs, hollow cathode glows, and two kinds of discharges in c rossed EXB fields: Penning and magnetron. At the present time, plasma catho de electron guns provide beams with transverse dimension from fractional mi llimeter up to about one meter, beam current from microamperes to kiloamper es, beam current density up to about 100 A/cm(2), pulse duration from nanos econds to dc, and electron energy from several keV to hundreds of keV. Appl ications include electron beam melting and welding, surface treatment, plas ma chemistry, radiation technologies, laser pumping, microwave generation, and more. (C) 1999 American Institute of Physics. [S1070-664X(99)03605-8].