Generation and control of reactive species in low temperature atmospheric pressure plasma sources.

Abstract

This work presents results of novel numerical studies investigating the interaction of plasma, gas and heat dynamics for a variety of popular source geometries. Plasma produced chemistry and heat flux reaching a treatment surface is investigated offering fundamental insight into induced plasma effects. Control opportunities for reactive species delivery and heat limitation is investigated in this context. The mixing of helium and air species in a corona plasma jet(’plasma needle’) is shown to define the shape and composition of the plasma region. Numerical analysis reveals an electropositive plasma core surrounded by an electro-negative edge reflecting the gas mixture profile. This non-uniform plasma results in non-uniform reactive species production. Circular and annular killing patterns recently found on bacteria treated by the source is shown here to correlate with atomic oxygen distributions at the surface. Interaction of the source with an aqueous surface reveals hydrogen peroxide as the dominant species dissolving at this interface. Atomic oxygen produced by O2 admixing to helium in a capacitively coupled jet(’micro-Atmospheric Pressure Plasma Jet’) is shown to quickly convert to ozone for increasing device to surface separation. Gas heating is dominated by elastic electron collisions and positive ion heating. Power modulation of a capacitively coupled jet(’micro-Atmospheric Pressure Plasma Jet’) is demonstrated as a mechanism for control of reactive species and heat flux delivery to a surface. Power is found to be coupled extensively to the electrons with large initial electron losses leading to weak interference between successive modulation phases. Frequency variation in a dielectric barrier discharge plasma source driven in the ~kHz frequency range is shown here to vary power deposition to the plasma by changing the interval between current pulses. O2(a1D) and O3 production is found to be coupled strongly to the O2 admixture