Discharge Plasma Parameters Research Articles

Estimation of mean electron energy in helium surface ionization waves on dielectric substrates

The determination of basic plasma parameters in atmospheric pressure discharges is critical to advancing their use in applications. Atmospheric pressure plasma jets have found use in the fields of medicine, agriculture, material modification and others. Atmospheric pressure plasma jets often generate plasma surface ionization waves (SIW) which interact with and propagate over surfaces. Electrical diagnostics are challenging in SIW due to high collision frequencies and small scale of the plasma discharge. This work employs a passive optical emission line ratio technique to estimate the mean electron energy in SIW over planar dielectric substrates. The method uses an intensity ratio of two helium triplet lines: He( 33S ) at 706.5 nm and He( 33D ) at 587.56 nm. A collisional-radiative model is used to correlate line ratio to mean electron energy and determine dependencies on electron density and He/air gas mixture. Mean electron energies ranging from 3–8 eV are determined in He/air mixtures and are found to remain constant as the surface wave propagates radially. This work provides a 2D, time-resolved, mean electron energy diagnostic for surface ionization wave propagation and validation of numerical modeling in atmospheric pressure systems with spatially varying He/air gas mixtures. The model in question is designed for use with any He line ratio in the n = 3 excitation level.

Design and testing of a Mini-RF plasma thruster with permanent magnets

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.

Discharge characteristics and parameter diagnosis of brush-shaped air plasma plumes under auxiliary discharge

Atmospheric pressure plasma jet (APPJ) can produce plasma plumes rich in active species, which has a wide scope of applications. From the perspective of applications, it is one of the hot issues in APPJ research to generate a diffuse plasma plume on a large scale. At present, large-scale plasma plume has been produced by noble working gases, which is more economic and valuable if it is reproduced by air used as the working gas. In this work, an APPJ with an auxiliary discharge is proposed, with which a large-scale air plasma plume with a brush shape is produced. Results indicate that the brush-shaped air plume can exist by changing voltage amplitude (<i>V</i><sub>p</sub>) in a certain range. The length and brightness of the plasma plume increase with <i>V</i><sub>p</sub> increasing. The waveforms of voltage and light emission signalindicate that the discharge can start at most once within half a cycle of applied voltage. The probability of discharge and the intensity of light emission pulse for each half a voltage cycle increase with <i>V</i><sub>p</sub> increasing, but the voltage value at the discharge moment decreases with <i>V</i><sub>p</sub> increasing. High-speed imaging study shows that the generation mechanisms of diffuse brush-shaped air plasma plumes and small-scale air plasma are similar, both originating from the temporal superposition of bifurcated normal flow light. In addition, optical emission spectra from the brush-shaped air plasma plume are utilized to study electron temperature, electron density, molecular vibrational temperature, and gas temperature. With <i>V</i><sub>p</sub> increasing, gas temperature is low and almost unchanged, while electron density, electron temperature, and molecular vibrational temperature increase. In addition, OH concentration of the plasma plume is investigated by laser-induced fluorescence, indicating that OH is uniformly distributed, and its concentration increases with the <i>V</i><sub>p</sub> increasing. All these results mentioned above are qualitatively analyzed.

Research of the vacuum thermocyclic nitrogen process in a plasma pulsing glow discharge

As a result of the studies, the regularities of the influence of vacuum thermocyclic nitriding in a pulsating glow discharge plasma parameters on the microhardness, the diffusion saturation depth, the magnitude and distribution of residual stresses in the hardened layers of steel surfaces are established. Based on the use of expert assessment methods and the results of a series of screening experiments, optimization criteria (endurance limit and corrosion resistance) and controlled factors for mathematical modeling of the formation of strengthened ion-nitrated surface layers are determined. A mathematical model of the technology of the formation of reinforced surfaces of the vacuum thermocyclic nitriding in a pulsating glow discharge plasma according to the criteria of endurance and corrosion resistance is obtained. An analysis of the studies showed that there are no general conclusions and recommendations on the selection of optimal technological parameters of the vacuum thermocyclic nitriding in a pulsating glow discharge plasma that would be used for the practical application of this technology. These circumstances confirm the need for further study of the vacuum thermocyclic nitriding in a plasma of a pulsating glow discharge of vacuum thermocyclic nitriding in a pulsating glow discharge plasma technology and the feasibility of its optimization.

Exploration of ITER operational space with as-built stiffness of central solenoid modules

The as-built stiffness in the ITER central solenoid (CS) modules (CSM1 thorough to CSM4 are currently manufactured) determines the range of vertical compression forces that can be tolerated by the CS modules during ITER operation. Since the as-built stiffness of the CS modules manufactured (∼32 GPa and ∼34 GPa for CSM1 and CSM2, respectively and similar for the other modules) has been reduced from the design value (53 GPa), the CS axial (vertical) force criteria have been updated assuming a conservative stiffness (25 GPa) with margins for all six CS modules. Initial analysis using the updated CS force criteria has revealed that this reduction affects only the plasma initiation with fully charged CS in the ITER 15 MA Baseline DT scenario, resulting in a slight reduction of poloidal magnetic flux, from 117.5 Wb to 116.2 Wb at initial CS magnetization. Therefore, the 15 MA Baseline scenario has been re-developed with an updated plasma start-up, and then the entire evolution of the CS and poloidal field coil parameters has been validated against all the coil currents, fields and forces criteria. To explore potential risks and opportunities for further optimization of scenarios, the equilibrium operational space (the plasma internal inductance versus the poloidal magnetic flux produced by the coils) at flat-top burn has been analyzed using the CORSICA and DINA codes. The three major ITER reference DT operation scenarios, 15 MA Q = 10 Baseline, 12.5 MA Q > 5 Hybrid and 10 MA Q ∼ 5 Steady-State, satisfy all the coil criteria including the CS force updated reflecting the as-built stiffness. The evolution of the plasma discharge parameters within the equilibrium operational spaces provided a guidance for potential optimization with margins.

Combined influence of airflows and a parallel magnetic field on the discharge characteristics of AC dielectric barrier discharge

The combined influence of airflows and a parallel magnetic field on an AC-driven dielectric barrier discharge plasma is experimentally investigated through image analyses, electrical measurements, and optical diagnoses. After applying a parallel magnetic field, more discharge filaments are generated during one discharge cycle. Besides, the electrical and optical diagnoses show that the magnetic field can increase the plasma parameters, such as the electron temperature and electron density. When airflows and a parallel magnetic field are applied in combination, the discharge uniformity presented in the long-exposure images is significantly enhanced by the airflows and slightly improved by the magnetic field. With increasing airflow velocity, the distribution of discharge filaments goes through four phases, namely, spot-like distribution, line-like distribution, cotton-like distribution, and stripe-like distribution, among which the stripe-like distribution exhibits the highest discharge uniformity. High-speed video analyses reveal that the improved discharge uniformity can be attributed to the changed breakdown positions and the increased number of filaments. Although airflow can significantly improve the macroscopic uniformity of the discharge, it leads to a decrease in the maximum current pulse amplitude, electron temperature, electron density, and gas temperature. Applying a magnetic field in flowing air can not only improve the discharge uniformity but also ensure that the discharge has high maximum current pulse amplitude intensity, electron temperature, and electron density. Based on the analyses of the electron trajectory and the estimation of the force condition of the micro-discharge remnants, the modulated charged particles, reduced electric field, and pre-ionization degree are responsible for the changed discharge uniformity and plasma parameters in the parallel magnetic field and flowing air.

Understanding non-equilibrium [formula omitted]/[formula omitted] chemistry in plasma-assisted low-temperature [formula omitted] oxidation

Ammonia represents one of most promising zero-carbon energy solutions to address the increasingly urgent climate change problem. However, the existing utilization of ammonia faces significant challenges from low chemical reactivity and high N2O/NOx emissions, which cause severe inefficiency issues such as cold start and cycle variability of power generation, and detrimental effects on air quality, respectively. A sustainable and energy-efficient approach to tackle the above challenges is low temperature plasma which enables non-equilibrium energy and chemical utilization of ammonia such as oxidation using renewable electricity. As such, this work, for the first time, explores plasma assisted ammonia oxidation at room temperature with a focus on unveiling non-equilibrium NOx/N2O reaction pathways by combining in-situ laser diagnostics with plasma modeling. We found that the non-equilibrium plasma controls the NOx formation by supplying O/H/N atoms via electron-impact dissociation and collisional quenching of excited species. The N2O formation follows a two-step mechanism, where electron-impact reactions first provide amine radicals which further react with NOx to generate N2O. These pathways facilitate a high-efficiency and environment-friendly operation of plasma assisted ammonia oxidation with enhanced reactivity and reduced NOx/N2O emissions through manipulating mixture compositions and plasma discharge parameters.

Effect of impurities in vacuum vessels on the plasma parameters in inductive discharges

The mechanisms affecting plasma by external and internal inputs must be understood for both semiconductor processing and controlled nuclear fusion, which require stable and steady-state plasmas. Among various factors that can change the state of plasma, detecting and controlling the plasma–wall interactions inside the reactor are challenging. In particular, although water is a commonly encountered impurity in most vacuum systems including process chambers, studies on the direct evidence of water effect on plasma are limited. Herein, we show that there is a clear negative correlation between the impurity density and the plasma density. A small change in water impurity could cause an immediate change in the plasma density because impurities contribute to increasing the total energy loss in the steady-state plasma sustainment. To observe the impurity effect distinctly, we conducted experiments under various conditions to analyze the effect of vessel impurities on plasma parameters, such as applied power, wall contamination, and wall materials. In the experiments, it is found that the plasma density is significantly influenced by the impurity density. The results were compared with the global model calculation and they are in agreement on the relative change of the electron density.

Effect of Fe2O3 Nanoparticles Dust on the D.C Plasma Characteristics with Mirror Magnetron

In this paper, the effect of iron oxide nanoparticles dust (Fe2O3 NPs) on the parameters of DC electric discharge plasma under vacuum in argon gas was studied with the presence of a mirror magnetron behind the electrodes (cathode and anode) at constant pressure and with different amounts of Fe2O3 nanoparticles. Calculations presented a reduction of the plasma emission intensity with the NPs content. Both the plasma density (calculated by Stark's broadening method) and the mean electron temperature (calculated using Boltzmann's equation) decreased with increasing the Fe2O3 nanoparticles dust content, which indicates clearly the effect of dust density on restricting the movement of charge carriers, which in turn reduces inelastic plasma collisions.

Simulation of DC glow discharge plasma with free-moving dust particles in the radial direction

A self-consistent fluid model is developed to investigate the radial distributions of dusty plasma parameters in a DC glow discharge, in which the extended fluid approach of plasma particles and the transport equations of dust particles are coupled. The electrical interaction between charged dust particles is considered in the model. The time evolution of radial distributions of dust density, plasma density, the radial component of electric field and the forces acting on dust particles when dust density tends to be stable, are obtained and analyzed under different discharge currents and dust particle radii. It is shown that the dust density structure is determined mainly by the radial electrostatic force, thermophoretic force and ion drag force in the discharge tube, and both discharge current and dust particle radius have an obvious effect on the transport processes of dust particles. The dust particles gather in the central region of the discharge tube for low discharge current and small dust radius, then dust voids are formed and become wider when the discharge current and dust radius increase. The plasma parameters in the dust gathering region are obviously affected by the dust particles due to the charging processes of electrons and ions to the dust surface.

A double‐mode planar argon plume produced by varying the distance from an atmospheric pressure plasma jet

AbstractAtmospheric pressure planar plumes are desirable for the applications of low temperature plasmas, such as rapid modification of large‐scale surfaces. Up to now, only single‐mode planar plumes with either a streamer mode or a filamentary mode have been reported in the literature. Distinctive from the single‐mode planar plumes, a double‐mode argon planar plume has been generated in this article, which operates in the streamer mode with a larger distance away from a plasma jet and transits to the filamentary mode with decreasing the distance. Discharge characteristics and plasma parameters are compared for the two modes. Results indicate that the streamer mode and the filamentary mode correspond to pulsed and humped discharges respectively. Fast photography reveals that the streamer‐mode plume is composed of stochastically branching streamers, while the filamentary‐mode plume results from a series of moving filaments similar to those in barrier discharge. In contrast to the streamer mode, the filamentary mode has lower excited electron temperature and vibrational temperature, whereas higher electron density and gas temperature. In addition, better hydrophilicity of polyethylene terephthalate surface is achieved in the filamentary mode.

INFLUENCE OF ION VISCOSITY ON THE DISTRIBUTION OF PARAMETERS IN THE SHEATH AT THE BOUNDARY OF A STATIONARY WEAKLY IONIZED STRONGLY NONISOTHERMAL PLASMA

A stationary weakly ionized highly nonisothermal plasma is considered in the hydrodynamic approximation. Taking into account the effects of ionization, recharging, and a self-consistent field, the effect of ion viscosity on the distribution of plasma discharge parameters in the sheath was investigated. Distributions of hydrodynamicion velocity and ion density, electron density, and self-consistent field potential in the sheath were obtained.

Interelectrode microwave glow discharge in atmospheric-pressure argon flow

The spatio-temporal structure and plasma parameters of a new type of glow discharge—atmospheric-pressure interelectrode microwave discharge in gas flow—were studied experimentally and numerically. A multi-electrode coaxial-type cold plasma torch developed for large-area surface treatment was used as a gas discharge device. The torch was supplied with microwave power (2.45 GHz, ∼100 W) via a coaxial cable by a typical wave-guide plasmatron. Self-sustained glow discharges were excited between the round ends of the rod-like electrodes and inner wall of the cylindrical discharge chamber near the outlet. The filamentation of the discharge channel in the near-electrode regions was detected by high-speed video filming. The dendritic self-similar (fractal) character of the filaments’ structure was revealed and analyzed. The branching factor and fractal dimension of this structure were estimated as 3 and 1.1–1.3, respectively. Using discharge gas temperature T g = 1200 ± 100 K, as determined from the emission spectroscopy measurements, the following discharge plasma parameters were obtained from numerical calculations: electron temperature eV and concentration – m−3, conductivity current density A m−2, and electric field strength V m−1.

Effect of Impurities in Vacuum Vessels on the Plasma Parameters in Inductive Discharges

Effect of Impurities in Vacuum Vessels on the Plasma Parameters in Inductive Discharges

In situ probe measurements of plasma parameters during the deposition of boron coatings by the magnetron method

The features of the probe technique are described and the results of measuring the parameters of plasma generated by a planar magnetron sputtering system with a pure boron target during coating deposition are presented. A feature of probe measurements was the use of heating the collecting surface of a single Langmuir probe. Heating led to a decrease in the electrical resistance of the boron film on the surface, which made it possible to carry out in situ probe measurements of the magnetron discharge plasma parameters during the entire process of boron coating. Keywords: plasma parameters, probe method, planar magnetron, boron films.

Зондовое in situ измерение параметров плазмы при нанесении покрытий бора магнетронным методом

The features of the probe technique are described and the results of measuring the parameters of plasma generated by a planar magnetron sputtering system with a pure boron target during coating deposition are presented. A feature of probe measurements was the use of heating the collecting surface of a single Langmuir probe. Heating led to a decrease in the electrical resistance of the boron film on the surface, which made it possible to carry out in situ probe measurements of the magnetron discharge plasma parameters during the entire process of boron coating.

Ion-induced electron emission cathode for a micro-newton HEMP thruster

An ion-induced electron emission cathode is applied for the first time in micro electric propulsion devices. In this investigation, ion-induced electron emission is operated on an annular LaB6 emitter for the neutralization and ion extraction of a microwave discharge HEMP Thruster (High Efficiency Multi-staged Plasma Thruster). A plume plasma diagnosis is performed with a Faraday probe and a retarding potential analyzer to analyze the discharge characteristics and plasma parameters. The results show that the ion-induced electron emission cathode can provides an emission current of over 0.4 mA. Compared with the condition with a thermionic cathode, there is a reduction in the thruster extracted ion current due to the deficiency of the emission current. The emission current shows different trends over anode voltage in different position configurations, which are affected by the incident ion flux and ion energy. Since the ion-induced electron emission cathode is free of power supply and propellant, it is of significant potential for low-power electric propulsion systems.

Adjustment of high-energy ion flux in BP-HiPIMS via pulsed coil magnetic field: plasma dynamics and film deposition

As an emerging and extraordinary plasma source, bipolar pulsed high power impulse magnetron sputtering (BP-HiPIMS) discharge has been widely concerned by academia and industry due to the ability to control the deposited ion energy. In the present work, with the intension of increasing the high-energy ion fraction and flux during deposition, the BP-HiPIMS is operated together with a solenoidal coil installed in front of the target. This intension is achieved by applying a pulsed coil current so that the ions generated during the high-power negative pulse can be manipulated to diffuse towards substrate and then arrive at the substrate surface during the positive pulse. Systematic investigations of discharge characteristics and plasma parameters for Ti target discharge in Ar gas have been made, illustrating that applying a pulsed coil current prior to the positive pulse onset for ∼50 μs is an optimal selection to obtain a larger fraction of high-energy ions. The complex plasma dynamics has also been explored using the particle-in-cell/Monte Carlo collision approach. To verify the statements realized by plasma measurements, the Ti films have been deposited on a floating Si substrate, whose microstructure and surface morphology are characterized by field emission scanning electron microscope and atomic force microscope. The deposition illustrates that applying a pulsed coil current prior to the positive pulse onset for ∼50 μs can prepare a thicker, denser, and smoother Ti film. The link between the plasma parameters and film microstructure is studied using the molecular dynamics simulations which show that the high-energy ions contribute to optimizing the adatom diffusion and mobility on growing film surface, which is more beneficial to get a smaller grain size and decrease the film surface roughness.

Plasma activation of methane for hydrogen in microwave liquid discharge by auxiliary gases: a way to realize efficient utilization of resources

Given the excited state species generated by the discharge gas can activate CH4 in gas-phase discharge and water in liquid-phase discharge. In this work, to make full use of the activation of auxiliary gases and maximize the energy utilization in liquid-phase discharge, the microwave liquid-phase plasma technology was used to study the activation of the CH4-H2O system by auxiliary gases for the first time, the photoelectric characteristics of discharge and discharge plasma parameters were analyzed. N2 and Ar were selected as auxiliary gases. The results showed that auxiliary gas could also activate CH4 and H2O in addition to the effective dissociation of reactants by electron collision, and the discharge gas-phase products were mainly H2. Compared with the discharge in the pure CH4-H2O system, under N2 and Ar atmosphere, the hydrogen production energy efficiency increased by 43.0% and 72.8%, respectively. This difference is mainly related to the selectivity of the active species produced by the two auxiliary gases to the original reactants and radicals. This study provides a simple and efficient method for plasma-assisted CH4 activation for hydrogen production.

Upgrade of the magnetic diagnostic system for restart of HT-6M operation

The HT-6M tokamak at the Thailand Institute of Nuclear Technology has been restarted. In order to ensure the smooth breakdown of plasma and obtain plasma discharge parameters, optimization of the poloidal field coils and upgrade of the magnetic diagnostics are described in this article. A perfect null field (stray field in the main chamber < 10 G) is obtained using an ohmic heating field. To obtain important information about the plasma, an external magnetic diagnostics system is designed and calibrated, including a Rogowski coil (measuring plasma current), a magnetic probe (measuring external field), diamagnetic loops (measuring β p) and so on. In order to realize high-frequency signal measurement and transmission, a series of frequency responses with the magnetic probe and transmission line are tested. Later, to verify the null field, a fitting code is developed to reconstruct the stray field in the vacuum chamber based on magnetic probe measurements and flux loops. The results show that the error is within 1.5%. This indicates the accuracy of the magnetic measurement system and ensures the preparation for the breakdown of plasma.