Plasma Grid Cathode Based on Arc Discharge in a Magnetic Field for Generating Electron Beam of Variable Diameter

The paper presents a modernized electron source with a plasma grid cathode. It was improved with a pulsed constricted low-pressure arc discharge that burns through a Ø 10 mm channel and then expands to Ø 100 mm towards the anode. The discharge system functioned under partial immersion in a non-uniform longitudinal magnetic field of up to (0.01-0.03) T. The gas-discharge system of the plasma cathode was characterized by a discharge current that flew around an additional electrode of a large diameter (70 mm) to ensure plasma redistribution. Azimuthal uniform generation of emission plasma was achieved near the emission grid Ø 85 mm in the plasma cathode. An electron source with such plasma cathode was capable of generating a pulsed (20-200) μs electron beam with an electron energy of (5-25) keV and a beam current amplitude of (50-500) A. The distribution of current density over the beam cross section was controlled by the magnetic field that influenced the discharge in the plasma cathode where an additional electrode that was used to redistribute the emission plasma. It is shown that a beam Ø 20-55 mm can be obtained after transporting a dense low-energy beam to a distance of 350 mm where inhomogeneity of energy distribution over the beam cross section is less than ± (5-10) %. Besides, it is possible to obtain a more compressed electron beam (up to Ø 10-15 mm) with less homogeneous current density distribution over the beam cross section. The beam diameter was changed by changing the magnetic field of two solenoids without changing the electrode system of the electron source.