Argon-helium Plasma Research Articles

Dust particle surface potential in an argon-helium plasma using the (r,q)-distribution function

Abstract In this paper, the dust particle surface potential for argon-helium plasma is evaluated analytically and numerically in the context of negatively charged dust particles by employing a power-law r , q -distribution function. Recent studies have reported the argon-helium plasma and conducted a brief theoretical and experimental survey. To deepen our understanding further, this study aims to analyze the argon-helium plasma comprehensively using the same pattern but with the r , q -distribution function. For this purpose, the current balance equations are derived for electron, helium and argon ions, when these charge species attain the quasineutrality condition. We numerically examined the currents of plasma species for a broad range of effective distribution function parameters r and q . It is revealed that the surface potential of dust particles is significantly affected by the parameters r and q , helium ion-to-electron temperature ratio, argon ion-to-electron temperature ratio, and helium ion to argon ion number density ratio. By incorporating the multi-ion (argon-helium) species, the significance of low-temperature non-Maxwellian dusty (complex) plasma is briefly examined.

Effect of plasma jet on electrochemical properties of silk fibroin hydrogel doped with PEDOT:PSS

AbstractIn this study, by injecting cold plasma into the silk fibroin (SF) solution, and adding poly (3,4‐ethylenedioxythiophene): polystyrene sulfonic acid (PEDOT:PSS) into the SF solution, the conductive SF‐PEDOT:PSS hydrogel modified by plasma was successfully prepared. The changes of the electrochemical parameters and structure of SF‐PEDOT:PSS hydrogels after plasma modification were observed with plasma discharge time (60, 120, 180 s) and the type of working gas (Ar, air, He) as variables. The results of electrochemical impedance spectroscopy show that both argon plasma and helium plasma can reduce the impedance of SF‐PEDOT:PSS hydrogel in the extremely low‐frequency range (10−2–10° Hz), and a longer discharge time shrinks the impedance, while the impact of air plasma on the impedance of hydrogel is not obvious. The capacitance results show that both argon and helium plasma can make the capacitance of hydrogel larger, and the longer discharge time leads to the larger capacitance. While air plasma can reduce the capacitance of hydrogel. The results of Fourier infrared absorption spectroscopy and X‐ray diffraction spectrum show that the secondary structure of SF is mainly β‐fold. The results of Raman show that PEDOT:PSS is successfully incorporated into hydrogel, and there exists random coil conformation of SF in hydrogel. The results of X‐ray photoelectron spectroscopy show that the SF‐PEDOT:PSS hydrogel mainly contains C, O, and N elements.

Plasma parameters profiles from Langmuir probe measurements in low-density, low-temperature plasmas in an axial magnetic field

Determining plasma parameters in low-density, low-temperature, weakly ionized, magnetised plasmas can be challenging, especially when using in-house-built Langmuir probes that may perturb the plasma. Radial profiles along the plasma column in such conditions present further challenges, not only because the densities evanesce at the edges, but also because of the presence of magnetic fields that may significantly affect the measurements. The analysis is presented here of radial profiles in pure argon and pure helium plasmas obtained using in-house-built Langmuir probes. The study was done in detail not only to obtain plasma parameter profiles, but also to gain an insight into the relevant physical mechanisms in the operating conditions of interest. Results from a plasma model were used to complement the analysis together with qualitative observations from resulting electron energy distribution functions. The main conclusions are: profiles obtained with the plasma model closely represent those obtained from Langmuir probe data, with irregularities qualitatively explained using electron density profiles obtained with Druyvesteyn and first derivative methods; plasma densities and electron currents are sufficiently small that no diamagnetic effects are evident; the strong magnetisation of the electrons is evident from the resulting characteristic Bessel-type density profiles.

Numerical Simulation of Plasma Jet Characteristics under Very Low-Pressure Plasma Spray Conditions

Plasma spray-physical vapor deposition (PS-PVD) is an emerging technology for the deposition of uniform and large area coatings. As the characteristics of plasma jet are difficult to measure in the whole chamber, computational fluid dynamics (CFD) simulations could predict the plasma jet temperature, velocity and pressure fields. However, as PS-PVD is generally operated at pressures below 500 Pa, a question rises about the validity of the CFD predictions that are based on the continuum assumption. This study dealt with CFD simulations for a PS-PVD system operated either with an argon-hydrogen plasma jet at low-power (<50 kW) or with an argon-helium plasma jet at high-power (≥50 kW). The effect of the net arc power and chamber pressure on the plasma jet characteristics and local gradient Knudsen number (Kn) was systematically investigated. The Kn was found to be lower than 0.2, except in the region corresponding to the first expansion shock wave. The peak value in this region decreased rapidly with an increase in the arc net power and the width of this region decreased with an increase in the deposition chamber pressure. Based on the results of the study, the local Knudsen number was introduced for detecting conditions where the continuum approach is valid under PS-PVD conditions for the first time and the CFD simulations could be reasonably used to determine a process parameter window under the conditions of this study.

Impact of high-energy effects on the formation of internal structure in copper particles

In the present paper, results of a study of the impact of high-energy effects on the surface morphology and on the formation of the internal structure in PMS-1 copper particles are reported. It is shown that the mechanical milling of the copper powder in a planetary mill leads to the formation of powder agglomerates with a layered structure consisting of numerous deformed ultrafine particles. It is found that the volume of the agglomerated particles involves the defects in the form of microcracks and closed micropores with some content of the initial gas. Subsequent treatment of the powder in an argon-helium plasma jet leads to the formation of dense particles as well as particles with distributed gas volumes or a single cavity. It was found that, as the molten metal interacted with localized gas volumes during the plasma treatment, local oxidation of the material occurred. A dispersion-strengthened structure with copper oxide compounds of a predominantly round shape, ranging in size from tens of nanometers to 7 µm and uniformly distributed over the particle volume, was formed.

Obtaining Spherical Powders of Grade 5 Alloy for Application in Selective Laser Melting Technology

In this paper, the process of obtaining a spherical powder of titanium alloy of the “Grade 5” brand using inductively coupled argon-helium plasma has been studied. The structure of titanium alloy was studied before and after the spheroidization process. The results of particle size and X-ray fluorescent analysis were also obtained. As a result of the analysis of the structure, it was concluded that the crystallite sizes and microstress values change. Keywords: additive technology, plasmachemical synthesis, spheroidization, titanium alloy, grade 5.

Comparative study of the Ar and He atmospheric pressure plasmas on E-cadherin protein regulation for plasma-mediated transdermal drug delivery

The effects of argon plasma (ArP) and helium plasma (HeP) jets on E-cadherin protein function have been tested in order to choose the working gas for a better plasma-mediated transdermal drug delivery. The plasma-mediated changes of the E-cadherin function and the skin penetration efficacies of epidermal growth factor (EGF) were monitored in vitro using HaCaT human keratinocytes and in vivo using hairless mice. The ArP showed higher efficacy for E-cadherin regulation and EGF absorption than HeP under the same applied voltage and the same gas flow rate. The ArP generates higher volume power density, higher discharge current peak, and more reactive species than HeP, especially for OH with the same operating parameters. Moreover, the effect of ArP on E-cadherin function was blocked by the use of a grounded metal mesh. Taken together, this study presents the possibility that the synergetic effect of negative charges with radicals plays an important role in plasma-mediated E-cadherin regulation, which leads to enhanced transdermal drug delivery.

Emission spectral diagnosis of argon-helium plasma produced by radio frequency capacitive discharge

Optically pumped metastable rare-gas laser (OPRGL) have been proposed to overcome the shortcomings of diode-pumped alkali-vapor laser in the recent years. The OPRGL promises to realize high-scale output. But how to achieve enough particle density of metastable atoms is still an open problem. Usually, plasma produced by discharge serves as a gain medium of the OPRGL. Here in this paper, we are to reveal the effects of different discharge parameters on the plasma properties, such as particle density of metastable argon atoms. Gas discharge at a radio frequency of 13.56 MHz is adopted to excite argon atoms. Emission spectrum is employed to study argon and helium radio frequency discharge of optically pumped argon laser at high pressure, different powers of discharge and various content of argon. Gas temperature is obtained by analyzing rotational spectrum (A2∑+ → X2Π) of OH radical generated by residual water vapor and comparing simulated spectrum with the measured spectrum. The electronic excitation temperature relating to electron temperature is obtained by the method of Boltzmann's plot. Stark broadening of the spectrum is used to determine the electron density. The results show that gas temperature rises slightly with the increase of pressure and varies little with content and discharge power changing. The electronic excitation temperature increases with the decrease of pressure evidently and decreases slightly with the increase of content. The electron density is on the order of 1015 cm-3 under various conditions controlled by us. Long time discharge test reveals that residual water vapor can lead to the decrease of electron temperature, and thus reducing the yield of argon metastable state. In conclusion, considering that the higher gas temperature can improve the collision relaxation rate of helium and argon, and the higher electron temperature can improve the rate of production of argon metastable state. Thus a proposal is put forward that appropriately heating gas and reducing gas pressure can obtain higher particle density of metastable argon. Furthermore, It can be found from these results that heating and cleaning the gas during discharge may be candidate methods to obtain and sustain the higher particle density in the plasma.

Validation of the van der Waals broadening method for the determination of gas temperature in microwave discharges sustained in argon–neon mixtures

Gas temperature is a key parameter to understand the processes that take place in a plasma because this temperature is related to the energy of the heavy plasmas particles which participate in the atomization of molecules and the formation of radicals from the substances introduced into the discharges. The method for the measurement of gas temperature in argon-helium plasma at atmospheric pressure, using the van der Waals broadening of spectral atomic lines, is adapted for the case of argon–neon mixtures. The Ar I lines 425.9 nm and 603.2 nm are determined as recommendable for such measurements, especially when the use of OH radicals is difficult or the contribution of these radicals to the plasma pollution is to be avoided.

Synthesis of thick photocatalytic titania surface layers by solution plasma spraying and subsequent treatment by pulsed laminar plasma jet

The two-stage method of synthesis of TiO2 photocatalytic surface layers with improved adhesion and cohesion, and photocatalytic properties based on vortex atmosphere solution precursor plasma spraying (SPPS) of thick anatase-rutile mixed coatings and their subsequent melting by pulsed laminar argon-helium plasma jet followed by auto-quenching and solidification is offered and approved for the first time. The titania coatings with increased rutile/anatase ratio characterized by high degree of crystallinity, increased specific surface area and permeability, and also advanced cohesion and bond strength with metal substrate, are sufficiently obtained for practice. The properties of the coatings were studied using X-ray diffraction (XRD) analysis, scanning electron and optical microscopy, BET- assisted measuring specific surface area and methylene-blue (MB) decoloration testing in an ultra-violet (UV) light room. Since the experimental determination of conditions of the post-treatment of the as-sprayed coatings by pulse plasma jet is rather labor- and power-consuming procedure, preliminary computer-aided evaluation has been carried out.

Argon and helium plasma coagulation of porcine liver tissue.

ObjectiveArgon plasma coagulation (APC) and helium plasma coagulation (HPC) are electrosurgical techniques that provide noncontact monopolar electrothermal haemostasis. Although these techniques have been widely used clinically during the last three decades, their in vivo effects on liver tissue remain unclear.MethodsWe investigated the effects of different power levels (10–100 W) of APC and HPC on liver coagulation in 11 Landrace pigs. Capillary blood flow and capillary blood flow velocity were recorded with a combined laser Doppler flowmeter and spectrophotometer. The temperature, clinical biochemical parameters, blood gas parameters, bile duct-sealing effect, and coagulation depth were measured.ResultsAPC and HPC significantly reduced the capillary blood flow and capillary blood flow velocity compared with baseline flow. No significant temperature change was measured on the liver surface immediately after coagulation. The clinical biochemical and blood gas parameters were not different before and after coagulation. The coagulation depth was positively correlated with the device power setting.ConclusionsThese results prove that APC and HPC provide sufficient superficial haemostasis. No significant systemic effects occurred following coagulation. The depth of the coagulation effect can be controlled through selection of the output power level.

Argon metastable production in argon-helium microplasmas

Microwave resonator-driven microplasmas are a promising technology for generating the high density of rare-gas metastable states required for optically pumped rare gas laser systems. We measure the density of argon 1s5 states (Paschen notation) in argon-helium plasmas between 100 Torr and atmospheric pressure using diode laser absorption. The metastable state density is observed to rise with helium mole fraction at lower pressures but to instead fall slightly when tested near atmospheric pressure. A 0-D model of the discharge suggests that these distinct behaviors result from the discharge being diffusion-controlled at lower pressures, but with losses occurring primarily through dissociative recombination at high pressures. In all cases, the argon metastable density falls sharply when the neutral argon gas fraction is reduced below approximately 2%.

Theoretical investigation of thermophysical properties in two-temperature argon-helium thermal plasma

The thermophysical properties of argon-helium thermal plasma have been studied in the temperature range from 5000 to 40 000 K at atmospheric pressure in local thermodynamic equilibrium and non-local thermodynamic equilibrium conditions. Two cases of thermal plasma considered are (i) ground state plasma in which all the atoms and ions are assumed to be in the ground state and (ii) excited state plasma in which atoms and ions are distributed over various possible excited states. The influence of electronic excitation and non-equilibrium parameter θ = Te/Th on thermodynamic properties (composition, degree of ionization, Debye length, enthalpy, and total specific heat) and transport properties (electrical conductivity, electron thermal conductivity, and thermal diffusion ratio) have been studied. Within the framework of Chapman-Enskog method, the higher-order contributions to transport coefficient and their convergence are studied. The influence of different molar compositions of argon-helium plasma mixture on convergence of higher-orders is investigated. Furthermore, the effect of different definitions of Debye length has also been examined for electrical conductivity and it is observed that electrical conductivity with the definition of Debye length (in which only electrons participate in screening) is less than that of the another definition (in which both the electrons and ions participate in screening) and this deviation increases with electron temperature. Finally, the effect of lowering of ionization energy is examined on electron number density, Debye length, and higher-order contribution to electrical conductivity. It is observed that the lowering of the ionization energy affects the electron transport-properties and consequently their higher-order contributions depending upon the value of the non-equilibrium parameter θ.

Enhancement of adhesion between antireflection coating and cellulose triacetate by surface pretreatment using argon-helium plasma

The adhesion of optical thin films on cellulose triacetate (TAC) was enhanced with surface pretreatment by argon-helium plasma. The optical properties, water contact angle, surface morphology, and thin film adhesion of TAC substrate that had been treated with different plasma gases were also investigated. An antireflection coating adhered well to TAC with an appropriate interface layer.

Presheath environment in weakly ionized single and multispecies plasmas

The presheath located near boundaries in weakly ionized plasmas is a rich environment in which charge exchange, and ion-ion streaming instabilities combine to establish the electric fields that accelerate ions to close to the Bohm velocity at the sheath/presheath boundary. Charge exchange sets the presheath scale length in weakly collisional plasma, in which ionization can be neglected. The transition of mobility limited ion flow near the bulk plasma to free fall motion close to the plate for single species plasmas is explored. Measurements in argon-helium multidipole plasmas of plasma potential with emissive probes and ion energy distribution functions with laser induced fluorescence are presented. These data show that the argon ions are speeded up by the presheath electric fields, argon ions are heated, and ion-ion instability is present as ions approach the boundary.

Mg II spectral line broadening in helium, oxygen and argon-helium plasmas

Stark widths (W) and shifts (d) of the astrophysically very important six (279.0777, 279.5528, 279.7998, 280.2705, 292.8633 and 293.6510 nm) singly ionized magnesium (Mg II) spectral lines in helium, oxygen and argon-helium plasmas have been measured at electron temperatures between 30 000 and 52 300 K and electron densities between 1.2 × 10 23 and 1.65 × 10 23 m −3 . They are the first experimental results obtained at electron temperatures higher than 20 000 K. A linear, low-pressure, pulsed arc has been used as an optically thin plasma source. The magnesium atoms, as impurities in the driving gases, have been introduced by erosion from the pure magnesium bands fixed on the discharge electrodes. Our measured Stark width and shift values have been compared to the existing experimental and theoretical data. We have found a good agreement with W and d values calculated by the semiclassical perturbation formalism (SCPF).

Two-temperature transport coefficients in argon–helium thermal plasmas

The knowledge of two-temperature transport coefficients is of interest in the modelling of flow in plasma processes and heat transfer. The transport coefficients in argon–helium plasmas at atmospheric pressure are calculated assuming that the kinetic electron temperature, Te, is different from that of the heavy species, Th. The electrical conductivity, the viscosity, the total thermal conductivity and the combined diffusion coefficients are calculated up to 30 000 K. The influence of the molar percentage of argon as well as that of the non-equilibrium parameter θ = Te/Th are investigated. The plasma composition is calculated using the modified Saha equation of van den Sanden et al. The most recent data to obtain collision integrals are also presented. It is shown that the viscosity and the combined diffusion coefficients strongly depend on θ, through the plasma composition and the collision integrals. The ion-dominated regime occurs all the more quickly as θ is high, resulting in a regime of interactions between charged species which induces a decrease of the viscosity and the combined diffusion coefficients. The electrical conductivity, which is directly linked to the electron number density, and the thermal conductivity increase as θ increases.

TWO-TEMPERATURE COMBINED DIFFUSION COEFFICIENTS IN ARGON-HELIUM THERMAL PLASMAS

From the derivation of two-temperature diffusion number fluxes of species proposed by Rat et al and that of ambipolar diffusion coefficients, combined diffusion coefficients introduced by Murphy at equilibrium are extended to non-equilibrium thermal plasmas, where the kinetic temperature of electrons Te is different from that of heavy species Th. Two-temperature ordinary and thermal combined diffusion coefficients are calculated in an argon-helium plasma at atmospheric pressure up to 30,000 К. Plasma composition is obtained using a non-equilibrium constant method. The dependence on the electron temperature of combined diffusion coefficients is analyzed for different mole percentages of argon in the mixture and for different values of the non-equilibrium parameter q = Te/Th Similar behaviors to those obtained at equilibrium are highlighted with a decrease in the combined diffusion coefficients, at fixed electron temperature, as q increases.

Advantage of Argon-helium Mixed Gas Plasmas for Carbon Determination in Glow Discharge Optical Emission Spectrometry.

For the sensitive determination of carbon in steel samples, an argon-helium mixture plasma gas was employed in glow discharge optical emission spectrometry. The emission lines of carbon have relatively high excitation energies, which implies that the excitations by helium whose ions and metastable atoms have larger internal energies could produce the excited states of carbon more readily. Comparison in the calibration curves yields the detection sensitivity obtained with the argon-helium mixture was enhanced than with the argon gas alone by a factor of 3.

Transport coefficients of helium and argon-helium plasmas

Calculated values of the viscosity, thermal conductivity, and electrical conductivity of helium, and mixtures of argon and helium, at high temperatures are presented. In addition, combined ordinary, pressure, and thermal diffusion coefficients are given for the mixtures. The calculations, which assume local thermodynamic equilibrium, are performed for atmospheric pressure plasmas in the temperature range from 300 to 30000 K. The results are compared with those of previously published studies. Significant discrepancies are found; these are attributed to the improved values of the collision integrals used here in calculating the transport coefficients.