Secondary Emission from Metals by Impact of Metastable Atoms and Positive Ions

Abstract

Experiments on the secondary electron emission from nickel electrodes due to bombardment of positive ions and metastable atoms in a neon discharge under conditions simulating those at the cathode in a glow discharge are described. Measurements with a collector movable in a direction perpendicular to a fixed plane collector give approximate values of the proportion $\ensuremath{\gamma}$ of the apparent positive ion current which is actually carried by secondary electrons. Values of 15-50 percent are found depending on the experimental conditions and degree of purity of gas. A perforated plate behind which is situated a Faraday box is used to separate the effects of the ions and metastable atoms. A preponderant part of the emission is ascribable to the metastable atoms, but values of the number $\ensuremath{\alpha}$ of free electrons per positive ion, are found to be 14 to 20 percent, varying approximately linearly for ions of velocities of 75 to 150 volts. The secondary electrons originate at the surface of the collector with about 12.5 volts maximum initial velocity.