In this work, we first produced microwave plasma ball, then changed the ball into a microwave plasma jet by flowing a working gas through a nozzle. The effect of working gas on the thermal characteristics of the plasma ball and atmospheric pressure microwave plasma jet was investigated. We used resonant absorption scheme by a metallic antenna inside a chamber in which led to the ionization of surrounded gas forming the plasma. A commercial magnetron at 2.45 GHz was used to produce plasma by various gases such as argon, nitrogen, air and argon/nitrogen composition. For analysis and identification of reactive species in the plasma, the optical spectroscopy (OES) was carried out. Optical emission spectroscopy of the plasma ball/jet revealed the presence of reactive neutral and excited atomic and molecular components generating from working gases and antenna materials. The antenna material has a significant impact on the jet length, so that maximum length of the plasma jet was observed in Fe-Ni antenna. The results of the experiments revealed that there is no significant change in the plasma jet length versus different gas flow rates and applied powers, while it is more sensitive to the gas type and antenna material.

Introduction The aim of this study was to investigate the sterilization potential of atmospheric pressure plasma jet (APPJ) and interactions of this technology with double-stranded DNA using the polymerase chain reaction (PCR) and single-strand conformation polymorphism (SSCP) techniques. Materials and Methods The plasma jet was produced through a high voltage sinusoidal power supply using a mixture of argon and oxygen gases with the flow rate of 1 L/min. Escherichia coli cells and double-stranded DNA (dsDNA) fragments were amplified by T7 universal primer through the PCR technique and treated with argon/oxygen APPJ at different exposure times. The data were analyzed by the agarose and polyacrylamide gel electrophoresis, SSCP and renewed PCR techniques. Results According to the results of the study, the APPJ could serve as an effective instrument for sterilization at > 30 sec discharge. The destruction of DNA was detectable by different techniques after 120 sec from APPJ discharge. Conclusion Our findings revealed that the active species of plasma can lead to cell death. These species may break or nick the dsDNA, exchange DNA nucleotides, and lead to transition and transversion mutations. These mutagenesis effects of APPJ might be the reason of microorganism cell death after the treatment in addition to other destructive effects of APPJ on macromolecules.

In this paper, using a Hoffmann glass reactor as an electrolysis instrument, the mechanism of liquid phase reactions resulting from the application of a DC atmospheric pressure discharge was studied experimentally for argon, oxygen, and nitrogen gases in an aqueous solution, and the effects of electron and positive ion radiations on the liquid phase were investigated separately for plasma anodic and cathodic interfaces. Electrical conductivity (EC), total dissolved solids (TDS), the concentrations of hydrogen cations , hydroxide anions , and oxygen gas of water were calculated and compared in conventional electrolysis and plasma-liquid anodic and cathodic interfaces for short time t=6min in periods of ∆t=2min. The results show that plasma anodic and cathodic interfaces can be used as a new electrolysis method to change and control the properties of liquids. In addition, nitrogen and oxygen plasmas were observed as a factor in increasing reactions and more considerable changes in water properties than argon plasma. That was due to the presence of reactive species derived from oxygen and nitrogen feeder gases in addition to species of atmospheric gases and water vapor. Further, liquid cathode discharge was more effective than liquid anodic discharge at producing more reactive species and changing water properties.

Background and objective: Non-thermal methods are suggested for decontamination of spices to preserve safety and quality of the products. In this study, effects of atmospheric pressure floating-electrode dielectric-barrier discharge plasma were investigated on red pepper powder, compared to gamma irradiation. Material and methods: To achieve the optimum time of treatment for decontamination, Escherichia coli, Bacillus cereus and Aspergillus flavus as microorganisms in red pepper were exposed to atmospheric pressure floating-electrode dielectric-barrier discharge plasma for 10, 20 and 30 min and the structural changes in microorganisms were investigated using scanning electron microscopy and DNA measurement following exposure. The red pepper was exposed to plasma for 20 min (optimum time) and 10 KGy gamma irradiation. Microbial count, color measurement and sensory evaluation of the samples were assessed before and after treatments. Results and conclusion: Results indicated that the density of surviving bacterial strains decreased when time of exposure increased and this decrease was significant after 10 min (P≤ 0. 05). The complete decontamination was carried out within 20 min. The deformation of cells and destruction of cell wall structures were seen in bacteria and mold following exposure. Data revealed that cold floating-electrode dielectric-barrier discharge plasma for 20 min inactivated red pepper microorganisms as well as gamma irradiation. As a conclusion, floating-electrode dielectric-barrier discharge plasma is an appropriate method to decontaminate the red pepper powder (regardless of color change) and can replace traditional methods without changes in the product quality and taste.

In this study, the performance of a cold atmospheric pressure plasma jet using neutral helium gas was experimentally investigated. Cold atmospheric pressure helium plasma jets have gained popularity in various processing applications due to their stability and enhanced reaction chemistry. The researchers examined the effect of applied voltage, flow rate, and electrode configurations on the length of the helium plume and analyzed the physical parameters of the plasma plume, including discharge voltage and average gas and discharge gap temperatures. The study revealed the presence of three operational modes: plasma bullets, a chaotic mode, and a continuous mode. Initially, the plasma jet operated in a deterministic chaotic mode after breakdown. Transitioning to the turbulent mode, increasing the gas flow rate resulted in a decrease in the plasma jet length. The flow rate required for laminar-to-turbulent transition increased with the applied voltage. By increasing the electrode separation and flow rate, the continuous mode was observed, where excited species remained within the inter-electrode space throughout the voltage cycle. Additionally, it was observed that the temperature of the discharge gap was close to room temperature. These findings provide valuable insights into plasma jet formation mechanisms and highlight the potential of tailoring plasma jet modes for specific processing applications.

The interaction of cold plasma with heterogeneous catalysts has led to some peculiar behavior, especially with silica (SiO2) seeding in presence of 2% alumina (Al2O3). In this paper, we have measured plasma parameters in low temperature arc plasma. I-V characteristics of Langmuir probes are plotted using the data obtained from the experimental set up for single probe method in arc plasma at atmospheric pressure. It is revealed that the used seed modifies the electron temperature of the plasma appreciably while the temperature of the gas in the surrounding remains almost unchanged. The single probe characteristics have been utilized to measure the electron temperature, floating potential, Debye length and electron density. It is found that electron temperature decreases whereas electron density increases appreciably after seeding the arc plasma. The decrease in electron temperature and increase in electron density to 99. 9% are observed after seeding the arc plasma with silica mixture as compared to those before seeding. Variations in plasma parameters such as electron temperature, electron density, plasma frequency and Debye length with discharge voltage are also plotted for the silica seeded arc plasma.

A helium cold atmospheric pressure plasma jet (HCAPPJ) driven by a commercial neon power supply was designed and utilized for inactivation bacteria. The generated reactive spices by HCAPPJ were investigated by optical emission spectroscopy. The reactive species of OH, OI, OI, N2 1+, N2 1+ and He were identified in the UV–, Vis wavelength region. The reactive species was not detected between 200 nm and 300 nm, as the flow rate of helium gas increased that led to the plasma temperature reducing to a value near to the room temperature. In this work, we studied the impact of HCAPPJ on Gram-positive and Gram-negative bacteria. The survival amounts of the two types of bacteria were decreased vastly when the rate flow rate was equal to 10 L/min.