Wall interactions with plasma generated by vacuum arcs and targets irradiated by intense laser beams

The theory of plasma-wall interactions in vacuum arc spots and in laser irradiated spots is reviewed in light of Langmuir's fundamental contributions to the theory of plasmas, sheaths, evaporation and electron emission. The mechanisms of plasma generation in the electrode and laser-target vapors are described. Models of sheath structures at surfaces which emit vapor and electrons are presented and the influence of the relation between the rates of electron and vapor emission on the electrical current continuity at the plasma-electrode boundary is discussed. The mechanisms of current continuity in the vacuum arc anode region, in the short vacuum arc, and in transient cathode spots are described. The important role of the near-target sheath in laser generated plasma is shown, indicating the effect of converting laser radiation absorbed in plasma into kinetic and potential energy of charged particles that impinge on the target. The description is summarized showing that understanding these phenomena relies on Langmuir's pioneering work.