Supersonic plasma jets formed by DC arc and ICP torch: common features and differences

Summary form only given. Some new techniques using remote thermal plasma for plasma chemistry and plasma processing have been developed. These techniques include plasma spraying, PECVD of diamonds, diamond-like and polymer films. In remote plasma deposition, thermal plasma is formed by means of one of traditional plasma sources. The chamber pressure is reduced with the help of continuous pumping. In that way the flow is accelerated up to the supersonic speed. The plasma expansion is controlled using a specific torch nozzle design. For practical applications it is very important to find the parameters that determine the gas dynamical and physical properties of supersonic plasma flows. With this aim, we analyze the common features and the differences between supersonic jets of plasma formed by direct current arc and induction torch. The plasmas flowing from the DC and ICP torches with slightly sub-atmospheric pressures through the supersonic nozzles (with the outlet Mach numbers 1 and 1.5) into low-pressure (2kPa) chambers are compared. The analysis is performed by means of optical emission spectroscopy combined with the numerical modeling. In our simulations we incorporate user-defined subroutines for two-temperature model into commercially available FLUENT program. The results show that substantial interrelated deviations from thermal, ionization and Boltzmann equilibrium can be found in both jets. We demonstrate that the ratio of the static pressure at the chamber inlet to the chamber pressure together with the Mach number at the nozzle outlet and the rarefaction parameter define the supersonic jet structure, and not the chamber pressure alone. We show that the physical properties of supersonic plasmas depend on the way and place of plasma formation. Namely, it is important to distinguish the configurations where the plasma is firstly formed and then accelerated (as in ICP torch) and the configurations where the plasma is formed and accelerated at the same time (a- in DC arc). The obtained results are useful for the optimization of plasma reactors for plasma chemistry and plasma processing applications.