Difference in shape and width of Dα lines in the overvoltage and abnormal glow regimes of open discharge in narrow gap

Abstract

Strong overvoltage discharges in a narrow gap between the solid cathode and grid anode (so called “open discharges”) are widely used for generation of the high-current electron beams. At low gas pressure (about 1 Torr) we revealed that discharge in the overvoltage gap stressed by stepwise voltage with amplitude up to 25 kV exhibits two regimes which follow one by one and generate the e-beams. The first of them produces the high-energy e-beam but the second generates the low-energy e-beam. The physical properties of these gas discharge regimes have been explored insufficiently. We have done the spectroscopic measurements of these regimes in D2 and found out that the overvoltage regime produces positive ions with high kinetic energy up to several keV but anomalous glow discharge forms the ions with energy of several tens of eV. The existence of high-energy ions in the overvoltage discharge provides a strong increase in the electron secondary emission from the cathode and possibly contributes to the ionization of the gas by fast ions. Our findings promote more insight into physics of the overvoltage discharge generating the high-current e-beams with energy up to 25 keV.