Generation of electron beams from vacuum arc plasmas

The status of experimental research and ongoing development of plasma cathode electron guns based on vacuum arc plasmas is reviewed, including some novel upgrades and application to various scientific and technological fields. The attractiveness of this kind of e-gun is due to its capability of creating high current, high current density, and broad electron beams. Existence of minimum current value to ignite a cathodic spot of vacuum arc, the arc current and so e-beam current cannot be lower then several amperes. Due to that fact, vacuum arc plasma e-guns operate in pulsed mode. A novel electron gun has been developed and investigated. The electron gun is based on a vacuum arc discharge with a hollow anode. This discharge unit is to provide a stable, uniform plasma surface from which a high-current density electron beam can be extracted. To produce the desired electron emission current the plasma density is controlled by magnetic field and arc current. Electron emission efficiency (ratio of the emission current to the arc current) was better than 90%. Electrons are extracted and accelerated up to energy about 20 keV. The electron extraction system provides acceleration and transport of a high-density beam. The beam passes through the 8 mm diameter aperture. The source produces long pulse (up to 100 /spl mu/s) electron beam with a high current density (up to electron beam up 80 A/cm/sup 2/). A strong external axial magnetic field provides beam focusing and propagation, and due to that fact the low pressures (1/spl times/10/sup -6/ Torr) can be reached. Different operating modes of the electron gun have been observed through the experiments.