Spontaneous plasma formation via electrical explosion of nanostructured metal surface layers in plasma–surface interactions

Abstract

The article is aimed at studying the issue of spontaneous, i.e., triggerless ignition of arcing plasma splashes due to explosive-electron-emission pulses at fiber-form nanostructured (W-fuzz) surface during plasma–surface interaction. There has been proposed an equivalent sputtering yield for arcing Yeff = 4.8 γ C/mg, where γ is the rate of plasma production (mass per charge) from a cathode by vacuum arc discharge. The ratio of the released-to-incident atoms Yeff can reach the value of about 10 for the plasma production rate of 2 mg/C. The increase in the plasma production rate γ has been estimated as (i) an increase in mass due to mechanical destruction of neighboring nanofragments and (ii) a decrease in ions average charge. The resulting twentyfold increase in γ at few-μm layers agrees with the experimental observations. The critical temperature Tcr (and corresponding cohesive energy Ecoh = 5 Tcr) for the W-fuzz nanostructure has been estimated as Tcr = 2 n/n0 eV, where n/n0 is the relative density of the W-fuzz nanostructure. It falls below 1 eV for typical fuzz layer thickness larger than few tenths of μm. This results in the experimentally observed reduction of the average W-ions charge in vacuum arc plasma.