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Optical emission spectroscopy (OES) is an important technique for plasma diagnostics. Random deviation is inevitable during the measurement of plasma emission spectra due to the imperfection of instruments and other interferences. On the other hand, inaccuracies in the collision cross-section data can lead to distortion of the collisional-radiative (CR) model. The coupling of theoretical and experimental error factors can pose difficulties for accurate diagnostics of plasma. This work presents the development of the OES method for xenon plasma that employs a neural network model to integrate prior information on the characteristics of instrument noise and model distortions, thereby improving the accuracy of OES diagnostics. The neural network model takes emission line ratios as input and normalized electron density as output and is trained using a dataset that is generated with a CR model and an instrument disturbance model. The neural network-based OES method is implemented to determine the electron density in a microwave discharge chamber and compared with a traditional OES method with a multi-variant fitting technique. A significant improvement on relative deviation of diagnostic results is observed, which promises a good prospect for further development. [ABSTRACT FROM AUTHOR]

Compared with traditional electric propulsion, RF plasma thruster have attracted much attention due to their characteristics of no electrodes, long life, and high ionization rate. In recent years, the development of micro-nano satellites has put forward requirements for the miniaturization, modularization, and integration of satellite thrusters, and the miniaturization of RF plasma thrusters has a broad prospect. In this paper, a mini-RF plasma thruster with a discharge chamber inner diameter of 10 mm is designed, and a magnetic field is generated around it by two annular samarium cobalt permanent magnets. The discharge state and plasma parameters of the mini-RF thruster are tested using optical emission spectrometry (OES) and target thrust stand. In the experiment, we changed the flow rate of argon gas, the presence or absence of a magnetic field, the power of the RF source and analyzed the effects of these factors on the mode transition, plasma density, electron temperature, and thrust. According to the experimental results, it is found that the magnetic field (maximum strength 0.14T) helps to increase the plasma density at low power but delay the jump power threshold of the CCP-ICP. [ABSTRACT FROM AUTHOR]

The atmospheric-pressure cold plasma jet that is a flowing afterglow of the interelectrode microwave discharge in Ar was investigated using various diagnostic techniques. Waveguide-type 2.45-GHz-plasmatron with the external 6-rod-electrode plasma torch was used as the cold plasma source. High-speed shadowgraphy was used to obtain spatio-temporal structure of the cold plasma jet. The periodic character of plasma generation was studied using electric probe floating potential measurements with an oscilloscope. [ABSTRACT FROM AUTHOR]

We present a description of a plasma-chemical facility designed for synthesis of micro- and nanoparticles using the radiation of a high-power gyrotron. The facility has been developed at the Plasma Physics Division of A.M.Prokhorov General Physics Institute of the Russian Academy of Sciences. The facility includes a plasma-chemical reactor, a gyrotron unit, an in-line calorimeter, a diagnostic system, which ensures video and spectroscopic measurements, balance measurements of the microwave radiation, and thermal imagery measurements, a chemical unit for specimen preparation and analysis of synthesis products, an electronic logging unit, and a specimen labeling system for organization and storage of a large amount of experimental data and specimens. [ABSTRACT FROM AUTHOR]

The electrophysical parameters of plasma, concentrations of fluorine atoms, and kinetics of reactive-ion heterogeneous processes in the CF4 + C4F8 + Ar + He mixture with the variation of the Ar/He ratio and bias power under the conditions of the induction RF (13.56 MHz) discharge are studied. The study scheme included plasma diagnostics by the Langmuir probes and optical emission spectroscopy, and also measurement of the rates and analysis of ways of etching SiO2 in the approximation of effective interaction probability. It is found that substitution of argon by helium has a meaningful effect on the kinetics and fluorine atom concentration by the parameters of electronic component of plasma. In contrast, an increase in the bias power slightly impacts the composition of the gaseous phase but is accompanied by a proportional change in the energy of the ion bombardment. It is found that, within the studied range of conditions, the process of SiO2 etching is characterized by the absence of ion-limited stages; moreover, the behavior of its rate is determined by the kinetics of the heterogeneous reaction Si + xF → SiFx. The variable value of the effective probability of this reaction keeps track of the variation in the proportion of free active centers determined by the rates of deposition and decomposition of the fluorocarbon polymer film. [ABSTRACT FROM AUTHOR]

Plasma density in a magnetized, capacitive-coupled, radio frequency (RF) discharge has been determined using the electrical impedance characteristics of the discharge. The effective impedance between the parallel plate electrodes has been treated as an equivalent electric circuit consisting of resistive and reactive components, expressed in terms of high-frequency plasma conductivity. Hence the model is used to connect the externally measured RF voltage, current, and their relative phase to plasma density. Additionally, a triple Langmuir probe (TLP) is used to substantiate the results of the electrical impedance model. The plasma density obtained using the direct probe measurement is found to be in good agreement with those determined from the passive measurements based on electrical impedance of the discharge as outlined in this article. [ABSTRACT FROM AUTHOR]

Plasmas interacting with liquid microdroplets are gaining momentum due to their ability to significantly enhance the reactivity transfer from the gas phase plasma to the liquid. This is, for example, critically important for efficiently decomposing organic pollutants in water. In this contribution, the role of â‹...OH as well as non-â‹...OH-driven chemistry initiated by the activation of small water microdroplets in a controlled environment by diffuse RF glow discharge in He with different gas admixtures (Ar, O2 and humidified He) at atmospheric pressure is quantified. The effect of short-lived radicals such as Oâ‹... and Hâ‹... atoms, singlet delta oxygen (O2(a 1Î"g)), O3 and metastable atoms of He and Ar, besides â‹...OH radicals, on the decomposition of formate dissolved in droplets was analyzed using detailed plasma diagnostics, droplet characterization and ex situ chemical analysis of the treated droplets. The formate decomposition increased with increasing droplet residence time in the plasma, with ∼70% decomposition occurring within ∼15 ms of the plasma treatment time. The formate oxidation in the droplets is shown to be limited by the gas phase â‹...OH flux at lower H2O concentrations with a significant enhancement in the formate decomposition at the lowest water concentration, attributed to eâˆ'/ion-induced reactions. However, the oxidation is diffusion limited in the liquid phase at higher gaseous â‹...OH concentrations. The formate decomposition in He/O2 plasma was similar, although with an order of magnitude higher Oâ‹... radical density than the â‹...OH density in the corresponding He/H2O plasma. Using a one-dimensional reactionâ€"diffusion model, we showed that O2(a 1Î"g) and O3 did not play a significant role and the decomposition was due to Oâ‹..., and possibly â‹...OH generated in the vapor containing droplet-plasma boundary layer. [ABSTRACT FROM AUTHOR]

A circuit modeling approach for self-sustained capacitively coupled microwave plasmas is introduced and validated in this article. The model solves the particle balance equation using a novel circuit optimization scheme to calculate the plasma parameters like electron density, sheath thickness, and electron temperature for a given input power, operating frequency, gas type, and pressure. While the existing models capture the ohmic loss in the bulk plasma region, the proposed model also takes into account power required to sustain plasma which proves to be considerable for higher electron densities. The model is rigorously validated using experimental results from two cases—one resonant and one non-resonant—both with self-sustained microwave plasma. As the post-processing results, other discharge parameters like sheath and plasma voltages as well as plasma reduced field are calculated. The proposed modeling approach can substantially simplify design and analysis of capacitively coupled microwave plasmas. [ABSTRACT FROM AUTHOR]

Ion-assisted surface processes are the basis of modern plasma processing. Ion energy distribution (IED) control is critical for precise material modification, especially in atomic-level technologies such as atomic layer etching. Since this control should be done in 'real time', it requires 'real-time' feedback using fast process sensors. In the general case of an industrial plasma reactor, when direct IED measurement is not possible, the IED can be estimated using the concept of a 'virtual IED sensor'. In this paper, a similar 'virtual IED sensor' is considered using an asymmetric dual-frequency (df) rf CCP discharge as an example. It is based on a fast calculation method of the IED at an rf-biased electrode. This approach uses the experimentally measured sheath voltage waveform and plasma density (or ion flux) as input data, and also includes Monte-Carlo simulation of ion motion in the sheath to take into account the effect of ion-neutral collisions. To validate this approach, experiments were carried out using various plasma diagnostics in several gases: argon and xenon as examples of plasma with atomic ions and nitrogen as an example of plasma with molecular ions. It is shown that in all cases it is possible to obtain an adequate IED estimation, close to the experimental one, in a reasonably short time (∼tens of seconds when using a modern PC). The results obtained demonstrate the possibility of using a virtual IED sensor in real plasma processing. [ABSTRACT FROM AUTHOR]

Few-layer graphene nanosheets were synthesised from ethanol using a microwave plasma torch. The stability of the discharge permitted us to directly observe and analyse two distinctive structures—a plasma zone and an assembly zone. Important plasma parameters and insights into the chemical processes taking place in these zones were gained using optical emission spectroscopy and digital imaging for a set of experimental conditions. The results of the plasma diagnostics were then correlated with the synthesised material properties, mainly obtained from electron microscopy and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Plasmas in contact with liquids are a rich source of OH radicals and have been extensively studied in the last decade to leverage the ability to generate chemically reactive species in gas phase plasmas to decompose organics. Multiphase transfer of OH radicals is highly transport limited and to overcome transport limits, the plasma activation of aerosols, small liquid droplets, interspersed in the plasma has been proposed. In this work, we report a combined experimental and modeling study of a controlled plasma–droplet interaction experiment using a diffuse RF glow discharge in He + 0.2% H2O with detailed plasma diagnostics, ex situ analysis of the plasma-induced chemistry in the droplet containing formate, droplet trajectory and size measurements. This enables a quantitative study of the reactivity transfer of OH from the gas phase plasma to the liquid phase and how its diffusion limitations impact formate decomposition in the water droplet. For a droplet with a diameter of 36 μm, we observed 50% reduction in formate concentration in the droplets after plasma treatment for droplet residence times in the plasma of ∼10 ms. These short droplet residence times in the plasma allow in some cases for droplet size reductions of ∼5% in spite gas temperatures of 360 K. A one-dimensional reaction–diffusion model was used to calculate the OH transport and formate oxidation inside the droplet and was able to predict the conversion of formate by plasma in a droplet without any fitting parameters. The model further shows that formate conversion is dominated by near-interfacial reactions with OH radicals and is limited by diffusion of formate in the droplet. The results show that a controlled plasma–micro-droplet reactor as reported in this study might be an excellent tool for detailed quantitative plasma–liquid interaction studies. [ABSTRACT FROM AUTHOR]

The stationary concentration method is used to study the mechanism of population of the hydrogen state in a low-pressure nonequilibrium plasma in a DC glow discharge and a microwave discharge. This state is used in plasma diagnostics based on the emission of Fulcher system bands. The limits of the applicability of the coronal model for the population of this state are considered. [ABSTRACT FROM AUTHOR]

In this study, the thermal characterisation of dielectric barrier discharge plasma actuation driven by radio frequency (RF) voltage waveform at low pressure is studied. The RF discharge images and voltage–current waveforms are quite different under 3 and 40 kPa. The thermographic method has been proposed for the spatial–temporal temperature field on the actuator surface