Diffuse Vacuum Arc on Lead Cathode: Plasma Parameters and Mechanism of the Charge Transfer on the Nonthermionic Cathodes

This article presents a study of an arc discharge with a diffuse current attachment on a cathode made of lead. The arc current was in the range of 10–27 A, and an average current density on the cathode was about 10 A/cm2. The saturated vapor pressure of lead at the operating cathode temperature of ~1.4 kK is ~1 kPa, and the thermionic current density is$\sim\!\!1~\mu $A/cm2. The spatial distributions of electric potential and the excitation temperature of atomic states were measured in the discharge gap. The existence of a negative anode potential drop was demonstrated. The ion energy and mean charge of heavy plasma particles were measured in the region behind the anode. A qualitative model of the cathode layer was considered, and its parameters were estimated. The hypothesis about the ion mechanism of charge transfer on the surface of the lead cathode was confirmed.