Effect of High Heat Flux of Helium and Hydrogen Plasma Jet on the Material Properties of Piezoelectric PZT-Ceramics

The study describes the behavior of plasma streamer discharges in helium and argon atmospheric pressure plasma jets fed by dielectric barrier discharge with the specific AC voltage waveform, which has hundred-kHz oscillations deviated from the zero level. The equivalent electrical and gas feeding conditions for producing both helium and argon jets have been provided. The plasma jet in helium is shown to have a diffusive structure and is formed by guided ionization waves, whereas an argon plasma jet is formed by numerous filaments which can have several branches on their ends. Repetitive stepwise plasma bullet formation has been observed in He plasma jet, whereas random and stochastic branching of the streamer has been recorded in Ar plasma jet. Both types of streamers have an approximately equal maximum of their length but significantly differ with the lifetime: they exist for about 1 and almost 8 μs in the argon and helium plasma jets, correspondingly.

This paper presents the evolution of striated discharge patterns in helium and argon atmospheric-pressure plasma jets as a function of gas flow rate and driving voltage. The striated patterns have been observed in helium and argon plasma jets at gas flow rates above 5 and 3 L/min, respectively. The striation patterns appear over the entire voltage range used for investigation (from 4 to 8 kV) in the helium plasma jet, whereas in the argon plasma jet, striation patterns appear over a limited voltage range (from 5.5 to 6.5 kV).

The use of a plasma jet for flame stabilization and promotion of combustion in supersonic air flows

Progress in the theoretical and experimental development of the plasma jet source and injection of hydrogen plasma and neutral gas jets into the Globus-M spherical tokamak is discussed. An experimental test bed is described for investigation of intense plasma jets that are generated by a double-stage plasma gun consisting of an intense source for neutral gas production and a conventional pulsed coaxial accelerator. A procedure for optimizing the accelerator parameters so as to achieve the maximum possible flow velocity with a limited discharge current and a reasonable length of the coaxial electrodes is presented. The calculations are compared with experiment. Plasma jet parameters, among them pressure distribution across the jet, flow velocity, plasma density, etc, were measured. Plasma jets with densities of up to 1022 m−3, total numbers of accelerated particles (1–5) × 1019, and flow velocities of 50–100 km s−1 were successfully injected into the plasma column of the Globus-M tokamak. Interferometric and Thomson scattering measurements confirmed deep jet penetration and a fast density rise (<0.5 ms) at all spatial points up to a radius r≈ 0.3a. The plasma particle inventory increase by ∼50% (from 0.65 × 1019 to 1 × 1019) did not result in plasma degradation.

OH radical plays an important role in biomedical, material, and combustion processing as well as in many other applications. Quantification of OH radicals in atmospheric pressure microwave plasma jets can be useful for understanding of OH formation mechanism and plasma generation. As reported previously, OH radicals exist in the far downstream (distance / plasma column length > 3) of an atmospheric pressure argon plasma jet. So far, we have confirmed that the similar phenomenon also exits in helium plasma jets, N 2 or O 2 mixed with argon plasma jets, and N2 or O 2 mixed with helium plasma jets. Here, the plasma column, which was generated using a microwave plasma source of 2.45 GHz, was typically of 3 mm long. Effects of addition of nitrogen and oxygen gases to argon in different mixing ratios, such as Ar: N 2 = 56:1, Ar: N 2 = 24:1, Ar: N 2 = 13:1 and Ar: O 2 = 27:1, were studied in detail using CRDS, OES and visual imaging. With addition of N 2 in argon plasma, a plume tail appears in the plasma jet column while addition of O 2 makes the plasma column unstable and more like a plume instead of a jet shape. Spectral simulations of emission spectra observed under various circumstances and temperature measurements clearly indicate that the gas temperature of Ar + N 2 plasma is higher than that of Ar + O 2 plasma. Absolute number densities of OH (v = 0, J = 3.5) along the plasma jet column were measured in these plasma jets. Dependence of absolute number density of OH on plasma power and gas flow-rate (variation in mixing ratios of N 2 and O 2 ) were also studied. The similar studies were carried out for addition of N 2 and O 2 in helium plasma jets with the mixing ratios of He: N 2 = 44:1 and He: O 2 = 41:1, respectively. As helium plasma jets are more stable, addition of N 2 or O 2 changes the jets into an unstable jet and a plume-like plasma, respectively. The results suggest that the addition of N 2 and O 2 in argon and helium plasma jets is helpful for OH radical generation but also makes the plasmas less stable.

Dielectric-barrier-discharge (DBD) plasma jets provide viable state-of-the-art nonthermal processes for a wide range of nanomaterials including particle transport and deposition. We report the interaction of argon and helium plasma jets with the particle aerosol, produced by ns laser ablation of a silver target and subsequently their transport for deposition on a distant substrate. The nanofeatures and functionality of the nanoparticles, entrained and deposited with the two plasma jets were compared using high-resolution electron microscopy, helium ion microscopy, scanning electron microscopy, ultraviolet–visible spectroscopy, and in terms of the SERS effect. The plasma jet facilitates the transport of the particle aerosol under the upshot of plasma ionic wind, caused by the high electric field in the plasma. Compared to the helium plasma jet, the argon plasma jet leads to a relatively large particle deposition and promotes the formation of aggregates. The helium plasma jet enabled the deposition of spatially well dispersed particles. In both cases, the deposited particle was crystalline and plasmonic active. The plasma-driven altered morphology, expedient particle transport, and formation of agglomerates or spatially well dispersed particles are explained in plasma-induced ionic-wind, and dusty plasma framework. The findings are novel and interesting from the perspective of plasma–surface deposition, surface nanoengineering, and nanomaterial processing for applications in sensing, catalysis, surgical tools, futuristic coating technology, and heat-sensible biological activities.

We employed UV–vis spectroscopy to monitor real-time changes in the oxygen tension and concentration of reactive oxygen and nitrogen species (RONS) in deionized (DI) water during treatments with helium (He) and argon (Ar) gas plasma jets. He and Ar gas jets are both shown to de-oxygenate DI water with He being more efficient than Ar, whilst the plasma jets deliver and regulate the concentrations of hydrogen peroxide (H2O2), nitrite (NO2−) and nitrate (NO3−) in DI water. The H2O2 and NO3− production efficiency varied between He and Ar plasma jets, but was similar for NO2−. Whilst DI water fully equilibrated with ambient air prior to treatment (de-oxygenated by both plasma jets) when DI water was first de-oxygenated by an inert gas jet treatment, both plasma jets were found to be capable of oxygenating DI water. These insights were then used to show how different combinations of plasma jet and inert gas jet treatments can be used to modulate O2 tension and RONS chemistry. Finally, potential further improvements to improve control in the use of plasma jets in regulating O2 and RONS are discussed.

The carburizing of titanium with argon-methane (0.1%) and argon-methane (0.1%)-hydrogen (2%) plasma jets at a pressure of 200 Torr was studied. The carburizing of titanium was not successful with the argon-methane plasma jet because the specimen was covered with graphitic carbon. A hard and thick TiC layer was formed by the argon-methane-hydrogen plasma jet in a short time without the deposition of graphitic carbon. Emission spectra from the plasma jets show that the addition of hydrogen increases the amount of CH radicals as well as decreases the amount of C2 and C in the plasma jet. The decrease of C2 and C suppresses the deposition of graphitic carbon and enhances the TiC formation.

Discharge characteristics of helium and argon planar plasma jets, impinging on a dielectric substrate in the ambient air, were comparatively investigated by high-speed photographs and electrical measurements. The helium plasma jet formed a luminous layer close to the dielectric surface and maintained homogenous in the transverse direction. The argon plasma jet propagated through a localized channel of ~1-mm diameter and spread on the substrate surface. Experimental results show that helium and argon plasma jets are glow-like and filament-like discharges, respectively.

In plasma cancer therapy, the inactivation of cancer cells under plasma treatment is closely related to the reactive oxygen and nitrogen species (RONS) induced by plasmas. Quantitative study on the plasma-induced RONS that related to cancer cells apoptosis is critical for advancing the research of plasma cancer therapy. In this paper, the effects of several reactive species on the inactivation of LP-1 myeloma cancer cells are comparatively studied with variable working gas composition, surrounding gas composition, and discharge power. The results show that helium plasma jet has a higher cell inactivation efficiency than argon plasma jet under the same discharge power. By comparing the concentration of aqueous phase reactive species and the cell inactivation efficiency under different working gases and discharge powers, it is demonstrated that the inactivation efficiency of LP-1 myeloma cancer cells is strongly correlated with the concentration of peroxynitrite (ONOOH/ONOO−).

The efficacy of helium (He) and argon (Ar) plasma jets are being investigated for different healthcare applications including wound and cancer therapy, sterilisation and surface disinfections. Current research points to a potential link between the generation of reactive oxygen and nitrogen species (RONS) and outcomes in a range of biological and medical applications. As new data accrue, further strengthening this link, it becomes important to understand the controlled delivery of RONS into solutions, tissue fluids and tissues. This paper investigates the use of He and Ar plasma jets to deliver three RONS (hydrogen peroxide—H2O2, nitrite— and nitrate—) and molecular oxygen (O2) directly into deionised (DI) water, or indirectly into DI water through an agarose target. The DI water is used in place of tissue fluid and the agarose target serves as a surrogate of tissue. Direct plasma jet treatments deliver more RONS and O2 than the through-agarose treatments for equivalent treatments times. The former only deliver RONS whilst the plasma jets are ignited; the latter continues to deliver RONS into the DI water long after the plasmas are extinguished. The He plasma jet is more effective at delivering H2O2 and directly into DI water, but the Ar plasma jet is more effective at nitrating the DI water in both direct and through-agarose treatments. DI water directly treated with the plasma jets is deoxygenated, with the He plasma jet purging more O2 than the Ar plasma jet. This effect is known as ‘sparging’. In contrast, for through-agarose treatments both jets oxygenated the DI water. These results indicate that in the context of direct and indirect plasma jet treatments of real tissue fluids and tissue, the choice of process gas (He or Ar) could have a profound effect on the concentrations of RONS and O2. Irrespective of operating gas, sparging of tissue fluid (in an open wound) for long prolonged periods during direct plasma jet treatment, could have implications for healthy tissue function; whilst through-tissue plasma jet treatment may provide a method to reperfuse oxygen-starved tissue. The assays described in this paper can be readily adopted (by others) and may support the future development of plasma sources to deliver specific (metered) doses of RONS.

Atmospheric pressure plasma jets (APPJs) have received considerable attention due to their potential for biomedical applications, material processing and analytical chemistry. In order to increase the understanding of the physical processes of these discharges, several parameters such as the voltage waveforms profiles, the device geometry and the working gas were studied. Recently it has been reported that one of the main factors that affect plasma discharge behavior is the target in front of the plasma jet 1. The aim of this work, is to investigate on the influence of a conductive target on helium and neon plasma jet characteristics.

The transportation of drugs through model tissues that are being treated by an argon plasma jet was investigated in this paper. Gelatin gel films were used to construct the model tissues and lidocaine was used as a representative drug. The argon plasma jet enhanced the penetration of lidocaine and the enhancement rate increased with the discharge voltage and the frequency. When the discharge power of the plasma jet was low, it was deduced that the enhancement effect was mainly attributed to the electric field of the plasma jet. The enhancement effect was holistic and was hindered by the macromolecules of gelatin in the model tissues. When the discharge power of the plasma jet increased beyond a threshold level, the surface streamers of the plasma jet produced a deformation effect in the model tissue, thereby resulting in a star-shaped pattern on the surface of the model tissue. In that case, the penetration enhancement of lidocaine was dominated by the deformation effect; however, it was mainly confined to the surface layer. For comparison, a helium plasma jet was also used to enhance the penetration of lidocaine. When the discharge power was low, the enhancement effect of the helium plasma jet was higher than that of the argon plasma jet because the He gas flow and the electric field of He plasma jet enhanced the penetration of lidocaine jointly; however, the enhancement effect of the Ar plasma jet was only attributed to the electric field. When the discharge power increased beyond a threshold level, the enhancement effects of the two plasma jets were almost the same.

This paper, deallng with the acetylene formation from n-pentame, n-hexane, n-heptane, cyclohexane, gasoline, kerosene amd gas oil, refers to the infiuences of the injection angle of the hydrocarbons on the formation of acetylene. The results obtaimed are summarized as following:(1) Acetylene yields were increased in the case that the in lection angle of the samples against the plasma jet was changed from 90°to about 45°in the direction of the cathode of the plasma torch, Its maximum yield, however, was 103g/kWhr with cyclo-hexane and /or 99g/kWhr with gas oil.(2) As for hydrocarbons of comparatively high boiling points such as petroleum, distlllates, preheating was not sufficient, and (consequemtly) gasfication of the samples was incomplete, Which induced the poor mixing of the sample and the plasma jet.

Atmospheric pressure plasma jets (APPJs) can be generated in capillary tubes flowing with pure helium and with admixtures of oxygen into the pure helium. The jet exiting the tube can be used for a variety of applications through surface interaction. In this study, a two-dimensional axi-symmetric model has been developed to provide insight into the evolution of capillary helium plasma jets with and without oxygen admixtures and their interaction with a dielectric surface placed normal to the jet axis. The model considers the gas mixing of helium and ambient air and the analytical chemistry between helium, nitrogen and oxygen species. Experiments were performed in conditions similar to those of the simulations in order to get qualitative agreement between them. The numerical and experimental results show that the evolution of the helium plasma jet is strongly affected by the introduction of oxygen admixtures. In particular, it was observed that the addition of oxygen admixtures in the helium gas promotes plasma bullet propagation on the axis of symmetry of the tube (in contrast to off-axis propagation for the pure helium plasma jet). On the other hand, the presence of the dielectric surface (a slab placed in front of the tube exit) forces the plasma bullet to spread radially. Furthermore, the plasma bullet speed decreases when the helium plasma jet is operated in the presence of oxygen admixtures. The numerical results also showed that He/O2 plasma jets induced much higher electric fields on the dielectric surface in comparison to the pure helium plasma jet.