Microarcing-enhanced tungsten nano and micro-particles formation in low pressure high-density plasma

In this article, tungsten dust formation kinetics in two distinct plasma regimes (glow and micro-Arc-Assisted glow discharge) are compared using the in situ time-resolved laser extinction method coupled to ex-situ Scanning Electron Microscopy analyses. This experimental study is carried out using low pressure/high density argon dual plasma that combines microwave and pulsed direct-current (tungsten cathode) discharges. Using this plasma system, we could access either to a sputtering glow regime (microarc-free) or to a micro-Arcing assisted glow regime by tuning the direct-current voltage and the pulse frequency. On the one hand, in the sputtering glow regime, only dust nanoparticles with sizes ranging from 75 to 150 nm are produced with a low density of ∼10 ¹² m ^-3 . On the other hand, in the micro-Arc-Assisted glow regime, microparticles in the range of 1-5 μm are produced along with a strong enhancement of nanoparticle production with density up to ∼10 ¹⁴ m ^-3 , and a broad size distribution ranging from ∼30 nm to 700 nm is observed. We show that micro-Arcing not only results in micro-meter sized particles through melting/solidification but also strongly promotes the production of nanoparticles in the 100 nm size range.