The Influence of Discharge Capillary Size, Distance, and Gas Composition on the Non-Equilibrium State of Microplasma

Abstract

The non-equilibrium state of microplasma from the mixture of He and N 2 was studied by exploring the rotational and vibrational temperatures of molecular nitrogen under various discharge conditions. At a varying gap distance of 1-3 mm (with a step of 1 mm) from the exit of the capillary to the water surface, the average rotational temperature of N 2 was found to increase from 983 to 1250 K while the corresponding vibrational temperature of N 2 was reduced from 4875 to 3099 K. Consequently, the average vibrational to rotational temperature ratio of N 2 was decreased from 4.96 to 2.48. By widening the capillary inner diameter from 100 to 200 mm, the average rotational temperature of N 2 was elevated from 891 to 1090 K whereas the average vibrational temperature of N 2 was dropped from 4662 to 3646 K and hence, the ratio of vibrational to rotational temperature of N 2 was lessened from 5.23 to 3.34. Moreover, with the addition of more nitrogen into the flow, i.e., by increasing the flow rate of N 2 from 0 to 15 sccm (with an interval of 5 sccm), the average rotational temperature of N 2 was intensified from about 942 to 1404 K, whereas the corresponding vibrational temperature of N 2 was reduced from 5011 to 3254 K. Therefore, the corresponding ratios of vibrational to rotational temperature of N 2 were declined from 5.3 to 2.3. The results demonstrate that the surface area to volume ratio of microplasma and gas conductivity have a significant effect on the nonequilibrium nature of He-N 2 atmospheric pressure microplasma.

Transparent Polyaniline Thin Film Synthesized Using a Low-Voltage-Driven Atmospheric Pressure Plasma Reactor

“…To prevent the unwanted transition of glow to arc discharge, a dielectric barrier that can easily control the current during discharge is commonly used, thus resulting in AC discharge [ 19 , 20 , 21 , 22 , 23 ]. When generating a DC discharge, it is common to expose the powered electrode to the discharge space, include a proper ballast resistor in the circuit to control the current, and ground the counter electrode [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ]. However, even when the tip of the tungsten wire electrode of the newly designed AP-plasma reactor was exposed to the discharge space, a ballast resistor was not needed because the AC voltage was applied at a frequency of about 30 kHz, and the glow discharge occurred in a single electrode structure without a ground electrode.…”

Temperature dependence of pattern transitions on water surface in contact with DC microplasmas

“…As we know, the gas temperature is determined by thermal balance between the heat energy absorbed by the plasma and the heat dissipated across the plasma boundary. By increasing the discharge gap distance, the surface to volume ratio of the plasma decreases, which weakens the dissipation of the heat energy, and leads to the rise of the gas temperature, and simultaneously to the rise of the temperatures of both electrodes [32].…”