Mode transition induced by gas pressure in dusty acetylene microdischarges: two-dimensional simulation

Radio-frequency microdischarge in acetylene is investigated by use of a fluid model and an aerosol dynamics model in a cylindrical discharge chamber. In this article, the results at a pressure of 100–500 Torr, a voltage of 80–150 V, and an electrode gap of 400–1000 μm are carefully analyzed and discussed. It is shown that two electron heating modes α and γ appear in the microdischarge, and the pressure-dependent transition from α to γ was accompanied by the abrupt decrease of electron density and electron temperature. The mode transition phenomenon is further confirmed by the variation of the electron temperature axial profiles, the profiles vary continuously from a center high at the pressure of 100 Torr to an edge high at the pressure of 500 Torr. Furthermore, in the α mode (100 Torr) the plasma density increases linearly with the increase of electrode gap, but decreases sharply with the increase of electrode gap in the γ mode (>100 Torr). The gas pressure and applied voltage effects on the nanoparticle density and degree of nonuniformity are also investigated. It has been shown that the gas pressure greatly influences the axial profiles of nanoparticle density and the values of the degree of nonuniformity, while the values of the plasma parameters (electron density and nanoparticle density) strongly depend on the applied voltage. (paper)