Kinetics of plasma particles and electron transport in the current-carrying plasma adjacent to an evaporating and electron emitting wall

Abstract

The paper reviews the vaporization phenomena at a target heated by heat flux from an adjacent plasma in vacuum and in low-pressure discharges. The kinetics of a nonequilibrium layer and the direct and returned mass fluxes formed in the vicinity of the target are described. The mechanism of cathode vaporization taking into account cathode electron emission in vacuum arcs is considered. It is shown that in vacuum arcs, the cathode electron beam relaxation region is an energetic zone which supports the generation of charged particles by atom ionization, balancing losses from ion motion towards the cathode and electron current. The mechanism of electron transport from the cathode to the plasma for cathode materials with strongly different thermal properties is considered. It is shown that the cathode electron current is controlled by a near-cathode space charge sheath whose structure depends on the thermo-physical properties of the cathode material. The potential structures has a large electric field at the cathode surface (like Cu), or a virtual cathode (W), or double plasma sheath (Hg), depending on the ratio of the electron emission flux to the vaporized atom flux, which in turn depends on the cathode material