Electrical and Optical Characterization of Cold Atmospheric Pressure Plasma Jet and the Effects of N₂Gas on Argon Plasma Discharge

Abstract

In this study, we conducted experiments to investigate the electrical and optical characteristics of a non-equilibrium Ar-N2 plasma discharge at atmospheric pressure. To obtain the plasma discharge we used our indigenously designed plasma generating device named CAPPLAT (Cold Atmospheric Pressure Plasma Torch) which was manufactured by Cresur Corporation. The plasma discharge obtained with only Ar gas was quite filamentary. So, to achieve a homogeneous discharge N2 gas was admixed. The effects of different volumes of admixed N2 gas were also studied. The optical emission spectroscopy was used to study the active charged species in the plasma discharges. The further increased volume of N2 gas further suppressed the emission intensity of Ar metastables but at the same time the emission intensity of the second positive system of nitrogen molecules (N2(C3Πu) enhanced significantly. It can be concluded that in Ar- plasma discharge, argon metastables are the main energy carriers but when N2 gas is added to the feeding gas (Ar) for plasma generation, the second positive system of nitrogen molecules (N2(C3Πu) become the main energy carriers. On the other hand the addition of the N2 gas doesn’t change the electrical characteristics of plasma discharge significantly. To identify the effectiveness of the CAPPLAT as a tool for sterilization, highly environmental stress resistant bacterial (Bacillus subtilis) endospores were treated for different durations. We could successfully deactivate the population of 1.0X107 to 4.0X107 Bacillus endospores/ml. The details of this experiment are discussed in our next paper.

Effects of Cold Atmospheric Pressure Plasma Jeton the Viability of <i>Bacillus subtilis</i> Endospores

“…The homogeneous plasma discharge from CAPPLAT had a very strong sporicidal effect because of the active species. The mechanism of the formation of active species had already been explained in our previous paper [10]. The energetic electrons collide with Ar molecules and make Ar metastables (Ar m ) and these energetic metastables sometimes de-excite along with the emission of radiation or change nitrogen molecules in the ground state into second positive systems ((N 2 (C 3 Π u )) which are the main energy carriers after the addition of N 2 gas whereas before the addition of N 2 gas Ar m were the main energy carriers.…”

“…The optical emission spectra was dominated by active species of Ar representing 4p -4s transitions, nitrogen active species representing N 2 second positive system (N 2 (C 3 Π u )) and a small peak representing OH radicals. The presence of OH radicles was because of ambient air or the gaseous impurities (detailed information is given in our previous paper [10]). Although OH radicals are known for their destructive effects on living cells but we can ignore their effects because of a very small quantity.…”

“…We used CAPPLAT (Model 9 Ne) and a hand-made plasma torch to generate non-equilibrium plasma at atmospheric pressure. The details of the system's structure and characteristics have already been reported previously [10]. The plasma torch comprised of two coaxial electrodes.…”

“…That device has also been commercialized under the name of "CAPPLAT" by Cresur Corporation [9]. This CAPPLAT (model 9 Ne) works at a sinusoidal feeding voltage of 20 kV (V pp ) and a frequency of 30 kHz using the mixture of Ar gas and N 2 gas to generate a homogeneous plasma jet which has been characterized previously [10].…”

Inactivation of Escherichia coli using atmospheric pressure cold plasma jet with thin quartz tubes

“…This guarantees the stability of the discharge system and satisfies the high activation effect of reactive species. The produced plasma can kill bacteria in open space, and it particularly overcomes the limitation of the discharge space of the dielectric barrier plate discharge system [12]. Furthermore, because AC power is used for APPJs, the system is simpler than laser and microwave discharge devices.…”