Current–voltage characteristics and mechanisms of electron emission from cold cathodes in a helium discharge

The abnormal discharge (AD) in pure helium and in helium containing molecular impurities was investigated. The obtained results were compared with the parameters of wide-aperture AD and different variants of ‘open’ discharge. It was shown that in all of the investigated types of discharges the current–voltage characteristics (CVCs) and, correspondingly, the emission properties of cold cathodes are determined mainly not by their material, but by the doping of cathodes with atoms of working gases and the purity of experimental conditions. With the impurity content less than 10−4% of the helium atom concentration, the CVCs begin to acquire S-shaped form, which is associated with a change in the electron emission mechanism. It was shown that the diversity of the CVCs is caused by uncertainty in the values of the secondary electron emission coefficients γ and the electron multiplication coefficient α in the cathode layer at reduced electric field strength E/N $?> > 103 Td. The reproducibility of CVCs and, correspondingly, emission properties of cathodes can be ensured by high purity of the working gas and by maintenance of the cathode doping only by the working gas atoms.