Hybrid model of neutral diffusion, sheaths, and the alpha to gamma transition in an atmospheric pressure He/H2O bounded rf discharge

作者：Ding, Ke^*; Lieberman, M. A.; Lichtenberg, A. J.

来源：Journal of Physics D: Applied Physics , 2014, 47(30): 305203.

DOI：10.1088/0022-3727/47/30/305203

• helium water discharge model
• atmospheric pressure rf discharge
• discharge sheaths

Water is a trace gas of interest for plasma-based medical applications. We use a two-temperature hybrid global model to simulate a chemically complex, bounded, He/H2O atmospheric pressure discharge, including 43 species with clusters up to H19O9+. The discharge is embedded in a larger volume, in which the trace gas fraction is controlled, leading to depletion of water within the discharge and diffusive flows of reaction products to the walls. For a planar discharge with a 1 cm electrode radius and a 0.5 mm gap, driven at 13.56 MHz, we determine the depletion and diffusion effects and the alpha to gamma transition, over a range of rf currents (100-1600 A m(-2)) and external H2O concentrations (500-10 000 ppm). The transition from the low power alpha-mode to the high power gamma-mode is accompanied by a collapse of the bulk electron temperature, an increase in the density and a decrease in the sheath width. At the highest external H2O concentration studied, there are no low current (alpha-mode) solutions because the sheath widths fill the device. The alpha-mode is recovered at larger gaps (e.g., 1 mm) or higher frequencies (e.g., 27.12 MHz). The higher mass cluster densities decrease rapidly with increasing gas temperature. Each simulation takes about two minutes on a medium size laptop computer, allowing exploration of a large input parameter space.

• 出版日期2014-7-30
• 单位东华大学