Non-equilibrium Plasma Source Research Articles

1D modeling of plasma streamers at ammonia-air flame conditions

Abstract This work is a self-consistent 1D modeling of streamers in ammonia-oxygen-nitrogen-water mixtures. A fluid model that includes species transport, electrostatic potential, and detailed chemistry was developed and verified. This model is then used to simulate the avalanche, streamer formation and propagation phases, driven by a nanosecond voltage pulse, at different thermochemical conditions derived from a 1D laminar premixed ammonia-air flame. The applicability of the Meek’s criterion in predicting the streamer inception location was successfully confirmed. Streamer formation and propagation duration were found to vary significantly with different thermochemical conditions, due to the difference in ionization rates. The thermochemical state also affected the breakdown characteristics which was tested by maintaining the background reduced electric field constant. Detailed kinetic analyses revealed the importance of O(1D) in the production of key radicals, such as O, OH, and NH2. Furthermore, the contributions of the dissociative electronic excitation of NH3 towards the production of H and NH2 radicals have also been reported. Spatial and temporal evolution of the electron energy loss fractions for various inelastic collision processes at different thermochemical states uncovered the input plasma energy spent of fuel dissociation and the large variability in the dominant processes during the avalanche and streamer propagation phases. The methodology and analyses reported in this work are key towards developing effective strategies for controlled nanosecond-pulsed non-equilibrium plasma sources used for ammonia ignition and flame stabilization.

Numerical optimization of non-equilibrium plasma source for surface processing of materials

Over the years, non-equilibrium plasma sources have emerged as a promising technology in surface processing of materials. Various strategies have been employed to make significant advancement in the technology. However, the process optimization is found to depend on different factors like power supply frequency, gas species and gas pressure. In order to control material processing outcome, it is necessary to control plasma parameters as per requirement. In the present work, a surface microwave generated non-equilibrium plasma source is proposed for material processing applications. The source comprises of rectangular waveguide system and a quartz tube, whose dimensions are optimized based on the electric field profile obtained within the plasma tube in the presence of the microwave (f = 2.45 GHz). Argon gas is allowed to flow through the discharge tube at a velocity of 10 m/s keeping its pressure at 1 torr. The microwave electric field within the discharge tube ionizes the argon gas medium resulting into plasma state whose properties are investigated using commercially available COMSOL Multiphysics® software. The inner surface of the discharge tube is then filled with dielectric beads (radius = 2 mm) and the effect of the dielectric constant on the plasma properties are studied. An investigation of ion flux at different positions in the plasma tube suggests that in the absence of dielectric beads, remote contact mode of operation can be preferred while in the presence of dielectric beads, direct contact mode of operation can be implemented. These results are of significance for direct as well as remote mode of surface processing of materials.

Evaluation of Oxidative Species in Gaseous and Liquid Phase Generated by Mini-Gliding Arc Discharge

The gliding arc discharge plasma reactors are known as a source of non-equilibrium plasma at atmospheric pressure. In the present study, generation of dominant reactive oxygen and nitrogen species in gaseous and liquid phase in water by the compact gliding arc device (mini-GAD) and corresponding bactericidal effects were investigated. Water and phosphate buffer solutions were used as model liquids. Mini-GAD is a strong source of nitrogen oxides (up to 800 ppm NO and 200 ppm NO2) that result in high concentrations of nitrites and nitrates in water solutions. The highest bactericidal efficacy towards Escherichia coli was achieved for non-buffered water solution.

Propeller arc: design and basic characteristics

A new atmospheric pressure non-equilibrium plasma source named the ‘Propeller Arc’ (PA) is developed using the concept of rotating electrodes. The PA device consists of a rotating cathode, driven by a motor, with one or more fixed anodes. Plasma is ignited at or near the narrowest gap as the rotating cathode passes by the anode and then it is extended up to a length of ∼66 mm or longer depending on the supplied power. This allows for efficient ignition, followed by a quick increase in plasma volume. The PA is similar to the widely used gliding arc (GA); however, unlike the GA, PA does not require imposed gas flow, and the PA discharge frequency can be easily controlled by the motor angular velocity. In this paper, the basic characteristics of PA are investigated using two different operation modes: pulse modulation and DC power. Discharge properties including electrical characteristics, time-resolved optical emission images, plasma electrical properties such as resistance and average electric field (discharge voltage divided by gap distance) and plasma power consumption are reported. Use of multiple anodes to increase the plasma volume is also demonstrated. As the PA has a compact design and is relatively easy to stabilize and control without the need for applied gas flow, it has potential to be adapted for many different applications such as nitrogen fixation, fuel and carbon dioxide conversion, waste, odor and hydrogen sulfide treatment, etc.

A study of the effect on human mesenchymal stem cells of an atmospheric pressure plasma source driven by different voltage waveforms

The effect of an atmospheric pressure non-equilibrium plasma on human mesenchymal stem cells was investigated. A dielectric barrier discharge non-equilibrium plasma source driven by two different high-voltage pulsed generators was used and cell survival, senescence, proliferation, and differentiation were evaluated. Cells deprived of the culture medium and treated with nanosecond pulsed plasma showed a higher mortality rate, while higher survival and retention of proliferation were observed in cells treated with microsecond pulsed plasma in the presence of the culture medium. While a few treated cells showed the hallmarks of senescence, unexpected delayed apoptosis ensued in cells exposed to plasma-treated medium. The plasma treatment did not change the expression of OCT4, a marker of mesenchymal stem cell differentiation.

Long and short term effects of plasma treatment on meristematic plant cells

In this paper, we will present results of plasma treatments of meristematic cells of Daucus carota. Plasma needle was used as an atmospheric pressure/gas composition source of non-equilibrium plasma in all treatments. Activity of antioxidant enzymes superoxide dismutase and catalase was measured immediately after plasma treatment and after two weeks following the treatment. Superoxide dismutase activity was increased in samples immediately after the plasma treatment. On the other hand, catalase activity was much higher in treated samples when measured two weeks after plasma treatment. These results show that there is a direct proof of the triggering of signal transduction in the cells by two reactive oxygen species H2O2 and O2−, causing enzyme activity and short and long term effects even during the growth of calli, where the information is passed to newborn cells over the period of two weeks.

Experimental assessment of a plasma-catalyst hybrid reformer for hydrogen production via partial oxidation of dimethyl ether

In this work, hydrogen is produced from partial oxidation reforming of dimethyl ether (DME) by a plasma-catalyst hybrid reformer under atmospheric pressure. The plasma-catalyst hybrid reformer which includes both plasma and catalyst reactors is designed. A spark discharge is used as a non-equilibrium plasma source, and it is used to ionize the mixture of DME and air. The performances of the reformer are characterized experimentally in terms of gas concentrations, hydrogen yield, DME conversion ratio, and specific energy consumption. The effects of discharge frequency, reaction temperature, air-to-DME ratio and space velocity are investigated. The experimental results show that the plasma-catalyst hybrid reformer enhances hydrogen yield when reaction temperature drops below 620 °C. At 450 °C, hydrogen yield of hybrid reforming is almost three times that of catalyst reforming. When space velocity is 510 h−1, hydrogen yield is 67.7%, and specific energy consumption is 12.2 kJ/L-H2.

Non-thermal Plasma Degradation of Anthraquinonic Dye in Water: Oxidation Pathways and Effect of Natural Matrices

AbstractNon-thermal plasma treatment by an electrical discharge generated above water was applied to study the destruction of anthraquinonic dye Acid Blue 25 in aqueous solutions. The direct current glow discharge above water sustaining in ambient air was used as a source of non-equilibrium plasma. The effect of operational parameters such as initial dye concentration, discharge current, pH and addition of salts on the substrate degradation was investigated. The highest G

Comparing the effect of different atmospheric pressure non-equilibrium plasma sources on PLA oxygen permeability

Plasma technology is widely adopted for polymer surface modification. In this work polylactide (PLA) samples have been exposed to the plasma region generated by three different plasma sources operating at atmospheric pressure: a floating electrode dielectric barrier discharge (FE-DBD), a novel linear corona discharge and a DBD roller. The sources have been supplied with a high voltage generator capable of producing pulses with a rise rate in the order of several kV/ns in order to obtain diffuse plasma and avoid local damage to the membrane; air and argon have been used as working gases. Pure oxygen permeation tests in PLA films have been carried out by means of a closed-volume manometric apparatus working at 35°C with a pressure difference of pure O2 of about 1 bar applied across the membrane. Tests have been performed shortly after the plasma treatment and also replicated at different times in order to investigate the durability of surface modification. The effects of voltage, pulse repetition frequency (PRF) and exposure time on the membrane surface characteristics and barrier property have been studied.

Mass analysis of an atmospheric pressure plasma needle discharge

Mass spectrometric measurements of a plasma needle (an example of atmospheric pressure non-equilibrium plasma source) were made for neutrals and ions. The measurements were performed for the same geometry as the standard plasma needles albeit for a somewhat increased gas flow. We discuss some of the problems of performing mass analysis at atmospheric pressures.The yields of N, O and NO radicals from the plasma needle were determined for different powers of the RF source and different flow rates of working gas. Positive ions generated by the plasma needle itself were measured for the first time. Significant conversion of feed gases (nitrogen and oxygen) into radicals and ions of N and O, and NO was observed as well as depletion of atomic radicals N and O which in chemical reactions form more complex molecules. Biomedical and nanotechnology applications of atmospheric pressure plasmas require a detailed understanding of the source, and mass analysis is perhaps the best technique to focus on chemical kinetics and in many ways interaction with surfaces.

Plasma Diagnostics Using Computed Tomography Method

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In the last decade, the range of applications of various low-temperature plasma sources has steadily grown. New applications require development of advanced diagnostic methods to control plasma parameters. Computed tomography is a powerful method which can provide much useful information on the plasma structure and its evolution in time. From a mathematical point of view, tomographic reconstruction is an ill-posed problem, which should be solved by using the regularization (in the large sense of the word) method. In this paper, we discuss a “technology” of tomographic study of plasma objects. It has been shown that numerical testing is a necessary component of the tomographic technology of plasma sources, particularly in situations with limited number of views and with ordinary discontinuities or high-gradient source functions. We are focused on a comparative analysis of the tomographic technology in equilibrium and nonequilibrium plasma sources. The analysis has been made using some examples from our practical diagnostics. The analyzed objects were as follows: nonequilibrium plasma of high-frequency low-pressure inductive discharge, equilibrium arc plasma of high-intensity discharge lamp, and methane plasma evolution in plasma-chemical reactor. We have concluded that the tomographic reconstruction in equilibrium plasma sources is the standard technology at present. The tomographic technology of nonequilibrium plasma sources is a developing approach, which has a great potential at making a contribution to understanding the fundamental processes and phenomena going on in the plasma. </para>

Experimental Study of a Minitype Atmospheric Non-equilibrium Plasma Source

A mini-type of plasma source was studied experimentally. The results showed that the plasma density, which was generated by an atmospheric non-equilibrium plasma source, rises with the increase in driving electric-field and the momentum of gas particles. For a driving electric-field of 56 kV/cm and a gas particles' momentum of 109 × 1−22 g · m/s, the ion density can exceed 1010/cm3 while the effective volume of the plasma source is only 2.5 cm2. This study may help develop a method to generate a minitype plasma source with low energy consumption but high ion concentration. This source can be used in chemical industry, environmental engineering and military applications.

The minimization of non-equilibrium plasma source at high pressure

The density of plasma produced by atmospheric non-equilibrium plasma source is the function of energy dissipation rate in ionization electric field and gas particles momentum. The experiment shows that the plasma density highly rises with the increasing of energy dissipation rate and gas particles momentum. When the energy dissipation rate of activation field is 2.18 Wh/m3 and the average gas particles momentum is 109×10−22 g·m/s, the air throughput of plasma source whose volume is only 2.5 cm3 can be up to 12 m3/h and the density of plasma can be up to 1010 cm−3. The research can develop a method of producing minitype plasma source which is low energy consumption but high ion concentration used for chemical industry, environmental engineering and military.

Twin injection-needle plasmas at atmospheric pressure

Twin injection-needle plasmas at atmospheric pressure are introduced as low-temperature nonequilibrium plasma source. The plasmas with long plasma columns of about 55cm are produced from one alternating current (ac) power supply as if each of the plasmas is a fraternal twin and shows different characteristics in plasma column length and gas temperature. The twin plasma columns are regarded as skinny rods with a uniform charge distribution, and the change of the plasma column lengths with different distances between the plasmas is compared with the change of the capacitance of the skinny rods presented as a model.

Experimental assessment of a combined plasma/catalytic system for hydrogen production via partial oxidation of hydrocarbon fuels

A combined reformation system, which includes both auto-thermal catalytic and non-equilibrium plasma units, is studied experimentally. The system is assessed for the practical application of hydrogen production via reforming of liquid gasoline-like fuels. The catalyst has been previously used for reforming of different types of hydrocarbons, demonstrating good performances in terms of hydrogen production for temperatures as high as 800°C. In this work, a non-equilibrium plasma source is coupled to the catalytic unit. A pulsed corona reactor is used as a non-equilibrium plasma source at atmospheric pressure. The performances of combined reformation system are characterized experimentally in terms of hydrogen yield and electric power consumption. Hydrogen conversion and byproduct composition are determined and quantified with respect to power consumption, reactor temperature, input reactant composition, and configuration of the experimental setup.