电弧等离子体电子数密度测量

Until now, the plasma parameters of supercritical (SC) fluids have remained largely unknown. In this study, two-dimensional electron density distributions were observed using Shack–Hartmann sensors for nanosecond-pulsed arc plasma in SC-CO2 (7.38 MPa) and high-pressure CO2 (1.59 MPa) generated in a 1 mm needle-to-plane electrode. The maximum electron density in SC-CO2 reached 1026 m−3, which was several times higher than that under the high-pressure CO2 (1.59 MPa), and was several-order higher than that of a typical arc discharge under vacuum (1019−22 m−3) and the atmospheric-pressure gas phase (1022−24 m−3). We investigated difference of the electron density decay characteristics between the SC and high-pressure CO2. The electron density for the SC CO2 has a longer decaying time constant than the high-pressure CO2, because the arc discharge under the SC CO2 maintains the arc temperature due to radiative re-absorption and one-order-smaller diffusion coefficient of the SC medium in contact with the plasma than that of the high-pressure phase. The results provide a database for numerical simulations of the pulsed-arc discharge in SC CO2 in the future.

No abstract available

Plasma technology stands at the forefront of numerous industrial applications, offering versatile solutions from materials processing to aerospace engineering. This study employs a single Langmuir probe technique operating at atmospheric pressure to scrutinize the transformative impact of silica seeding on low-temperature arc plasma. The investigation unveils a dynamic interplay of electrons and ions within the plasma, unveiling key electrical properties. The I–V electrical properties of the arcs plasma before seeding, having a floating voltage of –39 V, demonstrate electron and ion currents for varied probe voltages. The electrons’ density is calculated to be 2.11×1013 m–3, and the electrons’ temperature is at 6.25 eV. The I–V characteristics show a floating potential of about –35 V and –37 V after seeding an arc plasma using silica in the presence of aluminum oxide (2 % by weight) powder and grain, respectively. After seeding, it is discovered that the electron temperature falls to 1.18 eV for powder while 1.16 eV for grain and electron density rises to 2×1016 m–3 for powder and 1.84×1016 m–3 for grain. In addition, a notable fall in electron temperature and a discernible rise in electron density are seen. This non-equilibrium behavior is related to silica’s catalytic function, which is enhanced by the presence of aluminum oxide. Additionally, increased ionizing activity brought on by inelastic electron collisions causes the electron temperatures in the silica-seeded arcs plasma to rise with discharge voltage. These findings can be essential for enhancing plasma-based technologies in a variety of industrial applications because they provide insightful information on how silica seeding affects arc plasma properties

In this study, the electron density (ne ) and temperature (Te ) in an unmagnetized cascaded arc helium (He) plasma are precisely determined using cutting-edge laser Thomson scattering. In our experimental scope, ne is only 1018 m−3 and Te is less than 0.2 eV, both of which are substantially lower than in linear plasma devices (LPDs). The comparison of ne and Te values in He plasma with those in cascaded arc Ar plasma reveals that these two parameters are likewise significantly lower in He plasma than they are in Ar plasma on average. In comparison to Ar gas, the degree of ionization of He is low due to its high ionization potential, and diffusive loss dominates due to its light weight, both of which result in a lower ne . Meanwhile, these two characteristics render the three-body recombination interaction between electrons and He+ ions in He plasma insignificant, thus the electrons cannot be heated effectively, explaining why Te is lower. This study will provide foundational data and build the groundwork for a thorough knowledge of cascaded arc He plasma in LPDs and plasma windows.

No abstract available

The cascaded arc plasma source is a significant plasma-generating device capable of producing high-density, steady-state plasma in a low-pressure environment. The two most crucial physical parameters of the plasma are the electron density (ne) and electron temperature (Te). The laser Thomson scattering (LTS) technique provides an accurate method for measuring both ne and Te. In this study, we conducted diagnostic measurements of ne and Te for cascaded arc argon-helium (Ar-He) and argon-neon (Ar-Ne) mixture plasmas utilizing LTS technology. Furthermore, we explored the local thermodynamic equilibrium (LTE) state of the plasma by comparing the electron excitation temperature (Texc) obtained through optical emission spectroscopy (OES) with Te measured via LTS. Our results indicate that varying the dopant ratios of the gas mixtures, alongside the experimental currents and background pressures, influences both ne and Te. Specifically, these parameters are inversely proportional to the dopant ratio, while they are directly proportional to the background pressure and discharge current. Notably, at the same dopant ratios, ne and Te are slightly elevated in the presence of Ne dopants compared to those with He dopants. Additionally, the observed differences between Texc and Te suggest that the cascaded arc mixture plasma deviates significantly from the LTE state. This deviation is directly proportional to the dopant ratio and inversely proportional to the discharge current. The findings contribute to a deeper understanding of multicomponent plasmas and potentially enhance the applications of cascaded arc mixture plasmas.

Gliding arc air plasma exhibits significant application potential in energy, environmental protection, and other fields due to its non-equilibrium characteristics (high electron temperature and high concentration of reactive species). However, the spatial distribution characteristics of its electron temperature and electron density play a crucial role in determining plasma chemical efficiency. In this study, a multi-spectral imaging method combined with a collisional-radiative model was employed to conduct high-resolution spatial distribution diagnosis of the high-energy electron temperature and electron density of air gliding arc plasma, and the influence law of gas flow rate on plasma parameters was analyzed. The experimental results show that the electron temperature in the plasma core region can reach 4 eV, and the electron density is on the order of 1014–1015 cm−3, with significant spatial inhomogeneity. By adjusting the gas flow rate of the gliding arc generator, the distribution law of electron parameters in the gliding arc plasma generator can be significantly changed. The research results can provide important data support for optimizing the design of gliding arc plasma reactors and promoting their industrial applications, meanwhile, this diagnostic method may achieve effective parameter distribution monitoring in the industrial application of gliding arc plasma.

In recent years, magnetic fluid and arc plasma simulation models based on local thermodynamic equilibrium have provided an important aid to the analysis of the arc characteristics of switching appliances. However, it has been shown that when the current is small, the arc as a whole is deviated from the local thermodynamic equilibrium, but a clear correspondence between the arc current and the thermodynamic state of the arc is not given, which largely reduces the reliability of the simulation model. In this paper, from the perspective of arc spectral analysis, we build an arc experimental platform with spectral measurement function. Through this platform, the atomic spectral line data of the carbon electrode in the arc gap at different currents are measured, and the electron density data are obtained by the Boltzmann plot method and the Stark broadening method. The measured results show that when the current is greater than 40A, the electron density of the arc-firing process reaches above l022/cm3, which is consistent with the recognized data (>1022/cm3) under the local thermal equilibrium. When the current is less than 40A under the same condition, with the increase of current, the arc electron density increases and tends to l022/cm3• The change of arc electron density indicates that the arc thermodynamic state is more inclined to the nonlocal thermodynamic equilibrium when the arc current is less than 40A. From this, we can get the inference that the thermodynamic state of low-voltage AC arc and the size of arc current have a corresponding relationship, when the current is greater than 40A, the arc as a whole is more inclined to the local thermodynamic equilibrium state, and vice versa is more inclined to the non-equilibrium state.

Abstract: Atmospheric pressure gliding arc plasma is generated by a 50 Hz (0-13 kV) AC power supply. The electrical properties of the produced plasma are investigated with the help of an oscilloscope. In this work, the relationship between applied voltage, breakdown voltage, and discharge current is studied for air, argon, oxygen, and nitrogen gases. Similarly, the effect of the nature of gases on breakdown voltage and discharge current is studied. The power consumed by the discharge for different gases is obtained by current-voltage characteristics. It is found that among air, nitrogen, argon, and oxygen, argon consumes minimum and nitrogen consumes maximum power. Specifically, at the maximum applied voltage of 10.2 kV, oxygen and nitrogen consume approximately 56-57% more power than argon. Electron density, one of the most essential plasma parameters, is evaluated and compared using an electrical approach for several fading gases. The electron density is found to be increasing with the increase in applied voltage, and the value of electron density is found to be larger in argon discharge. Keywords: Gliding arc discharge, I–V characteristics, Power consumption, Discharge voltage, Electron density.

The thermionic vacuum arc (TVA) is a plasma source that generates highly ionized metal vapor plasmas via anodic evaporation, with independent control over plasma parameters through operational adjustments. This study investigates copper (Cu) plasmas produced by a TVA system under stable‐state conditions, focusing on the dependencies of electron temperature (Te) and electron number density (Ne) on operating parameters such as arc current (Iarc) and cathode filament current (If). Optical emission spectroscopy (OES) in the 200–1000 nm range was employed to analyze spectral line intensities of neutral Cu atoms. Te was determined via the Boltzmann plot method, yielding values between 4720 ± 250 K and 5370 ± 300 K as the Iarc increased from 300 to 1200 mA (at a fixed If of 18.5 A), while increasing the If from 16 to 19 A elevated Te from 4580 ± 250 K to 5180 ± 300 K, demonstrating distinct contributions of both parameters to electron heating. Ne was determined using Stark broadening analysis, revealing a weak dependence on operating parameters, with values ranging from (5.0 ± 0.8) × 1016 cm−3 to (8.9 ± 0.9) × 1016 cm−3). These findings highlight the TVA's unique capability to controllably tailor plasma properties, making it a promising candidate for advanced coating processes requiring precise plasma parameter modulation.

It is possible to determine the plasma parameters such as electron temperature/density and the external field by observing the light emission spectroscopically from the plasmas. The so-called plasma spectroscopy is used as one of the non-invasive plasma diagnostic methods which investigates the plasma dynamics. However, if we simply treat the effect of radiation reabsorption, which is neglected in the usual analytic model, the observed plasma may impair the understanding of this observation. It deals with the effects of radiation reabsorption on plasma spectroscopic diagnosis. The efforts will be made for linear divertor simulators and plasma spectrometers for high-density LHD plasmas where the optical thickness cannot be ignored. Thus, we discuss the influence of radiation reabsorption in the observations using He arc plasmas.

In recent years, research on pulsed discharge plasma in supercritical fluid has gathered attention of researchers due to the enormous possibility of its fusion effect. A supercritical fluid beyond the critical point inherent to a substance has both characteristics of liquid and gaseous phase, various researches on discharge plasma in supercritical fluid has conducted on not only discharge phenomena also material synthesis and its reaction fields. Particularly, discharge plasma in supercritical carbon dioxide has been many-studied both the viewpoint of fundamental research and its application1. On the other hand, there are few fundamental researches regarding on discharge plasma characteristics in supercritical nitrogen, although a few reports having application studies on fluid switches using high insulation properties of supercritical nitrogen2, The purpose of this research, it is clarify that pulsed discharge characteristic in supercritical nitrogen, which means to estimate a plasma temperature and electron density of thermal equilibrium plasma by the optical technique and so on. In series of experimental study, we have conducted by pulsed generator consists of Magnetic Pulse Compression circuit in order to stably generate pulsed discharge plasma in conditions such as a highly pressurized fluids. The experiments of an observation and measurement of pulsed arc plasma have carried out by using a needle-to-plate electrode placed inside high-pressurized reactor filled with nitrogen to produce discharge plasma. We will report the investigation results of the characteristics of pulsed discharge plasma in high-pressurized nitrogen including supercritical state.

In this work, we present the development and comprehensive characterization of an atmospheric pressure gliding arc plasma jet (GAPJ) operating in ambient air to generate non-thermal plasma. Through systematic investigation, the relationship between jet length and airflow rate indicates a positive correlation. Electrical and optical techniques are utilized to characterize the discharge, revealing an impact of applied voltage and gas flow rate on discharge parameters. Calculations are made for parameters such as electron density ((0.62−3.44)×1019) m −3, average power dissipation (9.85−40.50) W, and root mean square values of current and voltage. The impacts of applied voltages and gas flow rate on these parameters are also examined. Electron excitation temperature is determined using the Boltzmann plot method, yielding values within the range of (1.36−1.44) eV. Rotational and vibrational temperatures of discharge are analyzed, revealing values of (1373−2065) K and (2700−2405) K, respectively, under different operational conditions. The generated non-thermal plasma is confined to form a plasma plume although it consists of two diverging electrodes and offers promising applications for specified areas of sterilization and decontamination in the medical, pharmaceutical, and food processing industries.

The paper presents an enhanced version of an arc electron source designed for air ionization applications in a self-neutralizing air-breathing plasma thruster. The arc electron source is specifically suited for the air-breathing plasma thruster, as it allows precise control of mean electron energy levels. This paper focuses on the ionization aspects of air-breathing thrusters through the development of axially magnetized arc electron sources. The sources consist of a circular and coaxial configuration of a metallic arc plasma source coupled with a positively biased grid to extract electrons and control mean electron energy. The average mean electron energy of electrons in the arc electron source is regulated by adjusting the bias voltage of the grid within the range of 0 V – 300 V. To investigate the behavior of ion current density and electron density concerning pressure and mean electron energy, the current probe and magnetic filter were utilized. It was demonstrated that the circular electron source leads to enhanced ionization of airflow by achieving plasma densities greater than 1018 m−3. By utilizing a high-speed camera for the circular arc electron source, the arc spot was seen to move azimuthally due to the magnetic field. Furthermore, scanning electron microscopy and a conductance measurement system were employed for the coaxial arc electron source to examine the deposition and conductance of the electron extraction grid. While the grid underwent deposition of about 600 microns, the conductance was observed to increase/saturate with time and bias voltage, indicating an electrically “self-healing material”.

The diagnostic of high-density hot plasma is a challenging task due to its high temperature and electron density. Arc plasma is one of the typical hot density plasmas, and its diagnosis is the key to develop its new applications. In this paper, the temperature and density distributions of welding plasmas with different discharge currents are numerically simulated based on a Tungsten Inert Gas Arc Welding model, and the electron density distributions are calculated. Then propagation properties of broadband terahertz (THz) waves in the modeling arc jets are calculated by the finite difference time domain method. These results not only provide a preliminary theoretical guidance for in-depth understanding the problems of blackout in re-entry communication, but also develop a new idea for the terahertz diagnostic of plasma with high density.

We developed a steady-state high-density plasma source by applying a hollow cathode to a cascade arc discharge device. The hollow cathode is made of a thermionic material (LaB6) to facilitate plasma production inside it. The cascade arc discharge device with the hollow cathode produced a stationary plasma with an electron density of about 1016 cm-3. It was found that the plasma source produces a strong pressure gradient between the gas feed and the vacuum chamber. The plasma source separated the atmospheric pressure (100 kPa) and a vacuum (100 Pa) when the discharge was performed with an argon gas flow rate of 5.0 l/min and a discharge current of 40 A. An analysis of the pressure gradient along the plasma source showed that the pressure difference between the gas feed and the vacuum chamber can be well described by the Hagen-Poiseuille flow equation, indicating that the viscosity of the neutral gas is the dominant factor for producing this pressure gradient. A potential profile analysis suggested that the plasma was mainly heated within cylindrical channels whose inner diameter was 3 mm. This feature and the results of the pressure ratio analysis indicated that the temperature, and, thus, viscosity, of the neutral gas increased with the increasing number of intermediate electrodes. The discharge characteristics and shape of the hollow cathode are suitable for plasma window applications.

No abstract available

Plasma-based nitrogen fixation presents a promising alternative to conventional methods for NOx synthesis, with gliding arc reactors demonstrating high efficiency under ambient conditions. Current-limiting resistors (CLRs) are commonly used in experimental research to ensure stable discharge operation; however, most reported studies focus solely on reactor performance, overlooking the impact of these resistors on the overall process. This study systematically investigates the influence of resistors in the circuit on NOx concentration and energy consumption (EC) in a 2D gliding arc system. Three CLRs and two current viewing resistors were tested, and the case with a 20 kΩ CLR achieved the highest NOx concentration of 5.80 vol%. A key reason is that the CLRs maintained a stable glow-like discharge regime, suppressing undesired transitions of the discharge mode in a gliding arc. Optical emission spectroscopy measurements indicated that increased CLR values reduced the electron density and plasma temperature, potentially explaining variations in the achieved NOx concentration. Additionally, a significant disparity in EC was observed when accounting for total dissipated power, leading to a maximum EC increase of 5.65 MJ molN–1. These findings highlight the need to report the EC of both the reactor and CLR when evaluating plasma-based NOx synthesis efficiency.

This article deals with the investigation of dc plasma discharge of Ar–CO gas mixture in which the relative electron density and absolute temperature were measured. Relative electron density and absolute temperature were obtained for the mixture at discharge powers between 200 and 12 000 mW, and pressures between 0.1 and 0.5 mbar employing the radiative collisional model for several Ar–CO mixtures. Behavior of the electron temperature and relative number density are discussed. The absolute number density of the 1s5 was found to be higher than that of the 1s3 level.

Hydrogen plasma smelting reduction (HPSR) is an emerging technology for decarbonizing the iron and steel industry by utilizing hydrogen plasma as a reducing agent. This study investigates the effects of argon dilution and plasma-particle interactions in a non-equilibrium elongated arc of hydrogen for the in-flight smelting reduction of hematite particles. Using optical emission spectroscopy, electrical measurements, and x-ray diffraction analysis, we comprehensively characterize plasma properties and reduction performance. The results showed that the addition of iron oxide particles decreases the plasma resistance, followed by an increase in electron density. Strong non-equilibrium between electrons, gas, and particles was observed, with particles reaching 2800 K inside the plasma while gas temperature averaged 1800 K. This discrepancy is attributed to energy release from recombination and relaxation of excited species. Furthermore, increasing argon concentration was found to decrease the reduction degree due to a lower hydrogen partial pressure. A metallization degree of 50 % was achieved at 18 % argon dilution within a residence time of 18–30 ms, highlighting the role of excited hydrogen species in enhancing reduction kinetics. The findings provide critical insights into optimizing plasma reduction processes for sustainable metallurgy and demonstrate the potential of HPSR as a viable pathway for decarbonizing iron production.

The article presents the results of study of the non-self-sustained arc discharge with a magnetic field in zirconium vapors and the additional non-self-sustained discharge in E×B fields. Their main characteristics are given. The effect of the additional discharge on the electron temperature, plasma electron density, plasma potential and floating potential in the generated plasma flows of zirconium vapors is shown. It is established that even at low electric power, the additional discharge is able to double the density of plasma electrons in the flows. It is established that the anode potential drop in the arc discharge has a positive value over the entire range of discharge currents and decreases with its increasing. It is shown that the arc discharge in the anode material vapors is capable to generating plasma streams of zirconium vapors with the ionization coefficient from 60 to 90%. It has been established that the additional discharge in E×B fields is capable of increasing the ions fraction in the flows from 75 to 100% even at low arc discharge currents and can be used for the targeted regulation of ion fraction without changing the growth rate of the deposited films and coatings.

In this work, the influence of dry air on the electron density (ne) and electron temperature (Te) in a cascaded arc Ar plasma is firstly studied by the state-of-the-art laser Thomson scattering approach. The results reveal that a small amount of dry air can induce a sharp drop in ne, which is ascribed by the dissociative recombination reactions between electron and molecular ions formed in charge transfer reactions. With the increase in dry air ratio, Te exhibits a non-monotonic trend which initially increases and then decreases. This should be caused by the cooperation between super-elastic collision with highly vibrationally excited molecules and electron impact vibrational excitation to molecules. Additionally, the calculated electron density (necal) and electron temperature (Tecal) are derived using ne and Te obtained from the separate additions of N2 and O2, along with the respective proportions of N2 and O2 in dry air. It is found that both necal and Tecal closely match the experimentally measured values in dry air, which indicates that the impact on ne and Te are mainly dominated by N2 and O2 molecules and the interplay between nitrogen and oxygen, has minimal effect on the plasma parameters.

Modeling analysis of underwater pulsed arc discharge can predict the characteristics of plasma channels, providing theoretical guidance for the practical application of underwater pulsed discharge. Due to the complexity of experimental diagnostics for ‘kA’-level underwater pulsed discharge, there is currently a lack of precise experimental data to support the initial value selection and result optimization of the modeling. This paper established a plasma channel model for underwater pulsed arc discharge. In conjunction with the Saha ionization equilibrium equation, the model was capable of simulating the current, pressure, temperature, and electron density of the channel after gap breakdown. By utilizing spectroscopic diagnostic data and a multi-objective optimization algorithm, the initial values and key parameters of the model were reasonably determined. The simulation results were in good agreement with the experimental diagnostic results, reasonably representing the trends in electron density and blackbody radiation temperature. Moreover, the model was applicable for reasonably explaining the emission spectral mechanism of the arc channel and shock waves prediction under different discharge conditions.

No abstract available

No abstract available

During the circuit breaker breaking process, the behavior of the current zero arc is one of the key factors to determine the success of the gas circuit breaker breaking. Passive optical diagnostics can provide crucial microscopic information about the current zero arc. In this paper, different media current zero arc interference fringes are obtained by laser interferometry diagnostic technology, and the evolution of post-arc electron density is obtained through phase difference inversion. Compared with the decay rates of electron surface density in different arc extinguishing media, the results show that Air < CO2 < SF6, which is consistent with the excellent arc extinguishing performance of SF6 in practical engineering applications. By exploring the comprehensive control mechanism of gas arc post-arc decay process under different factors, this study provides a theoretical basis for the development of new circuit breakers.

A detailed characterization of electron parameters, particularly electron temperature and electron number density, is essential to understand the physics driving non-equilibrium plasma jets sustained by microwave electromagnetic fields. These parameters are often extracted from optical emission spectroscopy, a widely used and non-intrusive diagnostic method. Single point measurements along a line-of-sight are the most applied techniques, while performing 2D spatially resolved measurements continues to be a challenge. Although filter-based imaging techniques offer spatial resolution, spectral information is limited to only a few emission lines. Conversely, acquiring full spectra across a 2D region requires sequential point-by-point scanning, making real-time 2D mapping complex. In this study, we address these limitations by coupling hyperspectral imaging with collisional-radiative modelling to simultaneously extract and map, with an exceptionally high spatial resolution, the electron temperature, electron number density, and argon molecular ion number density. The results are obtained in both contracted (100% Ar) and expanded (Ar + 0.35% Xe) microwave plasma jets expanding into ambient air. The electron temperature, electron density, and molecular ion density exhibit distinct and structured spatial distributions, with electron temperature peaking and molecular ions accumulating at the edges.

The results of experimental studies of the shock-wave region of the supersonic plasma jet flow formed by a pulsed capillary discharge with a polymeric wall are presented. Using optical emission spectroscopy of high spatial resolution, a detailed picture of the evolution of the radial profiles of the electron number density and temperature along the initial section of an underexpanded plasma jet, starting from the capillary outlet and ending with the flow stagnation zone, has been obtained. It was found that the profiles of the electron number density and temperature reflect all the features of the shock-wave flow region, tracing the influence of intercepting, central and reflected shock waves.

AC air arcs are generated in medium-voltage (MV) power systems under the effect of harsh weather conditions, equipment aging, and high penetration of distributed generation, threatening equipment and public safety. The arc current and temperature are low due to the wide application of arc suppression devices. In this scenario, the MV AC air arc does not satisfy the local thermodynamic equilibrium (LTE) condition. In addition, the repeated arcing and extinguishing processes further complicate the arc discharge mechanism, which bring challenges in the modeling and detection of MV AC air arcs. Experimental methods are a direct and efficient approach to determine the properties of arc plasmas. In this study, a dual-wavelength Moiré deflection diagnostic system was established to determine the time evolution of the particle density and radial distribution of the temperature in an MV AC air arc without relying on the LTE assumption. The electron number density and heavy particle number density change transiently during the arc discharge process and change gradient along the radial direction. The heavy particle temperature and electron temperature were then calculated based on the measured particle number density. During the arcing stage, the temperature of the electrons exceeded that of the heavy particles significantly, and the arc deviated from LTE. Finally, the limitations of the traditional single-wavelength Moiré deflection method are analyzed. The classic single-wavelength Moiré deflection method, while capable of estimating heavy particle temperature in plasma, exhibits a significant error in electron density estimation compared to the dual-wavelength Moiré deflection method.

Langmuir probe diagnostics are a cornerstone of plasma characterization, providing critical measurements of electron temperature, electron density, and plasma potential. However, conventional swept Langmuir probes and other traditional electrostatic probes often lack the temporal resolution necessary to capture transient plasma behavior in dynamic environments. This paper presents the design and implementation of a fast-sweeping Langmuir probe system that is open-source, low-cost, and adaptable for a wide range of plasma applications. The probe system incorporates voltage sweeping to resolve rapid fluctuations in plasma parameters at a temporal resolution of up to 200 kHz. To validate its performance, the system was implemented in the 30 kW miniature arc jet research chamber, a high-enthalpy DC arc jet facility designed for prototype testing and development. Experimental results demonstrate the probe's capability to operate in extreme aerothermal conditions, providing time-resolved electron temperature and density along the flow's radial profile. This study establishes a robust and accessible Langmuir diagnostic solution for researchers studying transient plasma behavior in high-enthalpy environments.

Atmospheric pressure nitrogen series-arc discharge (SAD) plasma jet, under the influence of an external magnetic field, was used for $\text{NO}_{\mathrm{x}}$ synthesis. The optical emission spectroscopic (OES) technique was employed for the estimation of the nitrogen SAD plasma properties. The properties include rotational $(\mathrm{T}_{\mathrm{r}})$, and vibrational $(\mathrm{T}_{\mathrm{v}})$ temperatures, electron excitation temperature $(\mathrm{T}_{\mathrm{e}\mathrm{x}})$, and electron density $(\mathrm{n}_{\mathrm{e}})$. It is found that $\mathrm{T}_{\mathrm{r}}, \mathrm{T}_{\mathrm{v}}, \mathrm{T}_{\mathrm{e}\mathrm{x}}$, and $\mathrm{n}_{\mathrm{e}}$ are increased slightly both in the absence $(\mathrm{B}=0)$, and presence $(\mathrm{B}\neq 0)$ of magnetic field (B), with the increase in applied voltage. The increments of these plasma parameters can likely be occurred due to the increase in applied voltage. Because, the electrons gain more energies from the enhanced electric field. On the other hand, these plasma parameters are also enhanced due to the presence of $\mathrm{B}$ with respect to zero magnetic fields. This may happen due to the reduction of diffusion loss of electrons because magnetic field inhibits the movement of electrons in the radial direction. Further, the electrical power dissipation in the plasma is slightly decreased in the presence of magnetic field. For all other applied voltage, similar phenomena happened. This result may imply that the energy cost for synthesizing $\text{NO}_{\mathrm{x}}$ in water will be reduced.

A two-chord quadrature-heterodyne spatial optical interferometer has been developed specifically for making time-resolved measurements of line-integrated electron density in hypersonic plasma jets (Mach number $\mathrm{M}[]10$) in the range of $10^{15}-10^{18} \mathrm{~cm}^{-2}$. The time-resolved measurement of the plasma density of the jet is critical in validating the initial operating capability (IOC) of Shanghai Tech Gun1 (STG1) PJMIF-grade coaxial plasma gun. The interferometer utilizes a 300-mW, S-polarized 532 nm CW laser with a coherence length of approximately 100 m, requiring only one reference path for two probe paths. Two spatially separated optical probe beams are directed through the first flange window of the cylindrical experimental vacuum chamber and are subsequently reflected back by spherical mirrors. Negative phase shifts are consistently measured throughout shot-to-shot IOC experimental campaign and good repeatability is attained. The interferometer is capable of measuring line-integrated electron densities down to the order of corresponding to phase shift of $\sim 0.02 \mathrm{rad}$. The process of obtaining the interferometric data and its application in deriving the total jet density, jet mass, jet propagation velocity and jet length will be presented.

No abstract available

This study investigates the mechanism of discharge transitions in a radio frequency atmospheric pressure plasma jet (RF APPJ), with the aim of unraveling the underlying mechanisms behind the unexpected arcing-like filament formation on power electrode observed at lower power levels and the subsequent glow-to-arc transition (GAT) at higher powers. Through meticulous analysis of plasma parameter variations under varying power increment rates, this research offers crucial insights into the complex dynamics of plasma behavior. Detailed analysis of discharge current under different power increment rates exhibited distinct discharge phases as power increased, i.e., the normal glow phase, the abnormal glow phase, and the glow-to-arc transition. Notably, the arcing-like filament formation observed on the power electrode during the abnormal glow phase is indicative of complex plasma dynamics driven by the combined effect of thermal instability and the resulting thermo-field emission. Particularly noteworthy is the dynamic relationship between power increment rates and the duration of the abnormal glow discharge phase, shedding light on the multifaceted nature of thermal instability phenomena. Moreover, the ponderomotive force plays a crucial role in restricting thermo-field emission, thereby preventing the transition from glow to arc at low power levels. Additionally, the observed rise in electron density, electron temperature, and the emission intensity of reactive oxygen and nitrogen species during the abnormal glow discharge phase presents exciting possibilities for novel operational regimes characterized by lower gas temperatures. This study paves the way for enhanced understanding and control of atmospheric pressure plasma processes by highlighting the intricate interplay between power increment rates and discharge behavior, offering promising avenues for developing more efficient and stable plasma-based technologies.

The accurate calculation of physical parameters for an ice surface arc is fundamental to numerical research, with particle composition being a critical factor. This article introduces a linear dimensionality reduction technique to address the challenges posed by complex internal arc reactions in calculating particle composition. The method’s accuracy is validated by comparing the computed electron number density of the arc on the ice surface with the results of the emission spectrum. By combining the types of particles present in the arc on the ice surface identified by emission spectroscopy, this study analyzes how varying NaCl and H2O ratios affect the number density of charged particles in the arc. Results indicate that NaCl significantly increases the charged particle density in the arc, with a peak observed between the temperature range of 5000–7000 K, which shifts to higher temperatures as the proportion of NaCl rises. Conversely, H2O inhibits the rise in the number density of charged particles in the arc within the 3000–8200 K range, with stronger inhibition as the H2O proportion increases.

Microwave atmospheric pressure plasma jets (MW-APPJs) exhibit significant potential for diverse applications, i.e., hydrogen production, CO2 dissociation, water treatment, material processing and waste treatment due to their stable operation at atmospheric pressure and generation of highly tunable reactive species. For effective utilization of MW-APPJs, a detailed understanding of the operational conditions that influence plasma parameters is essential. The present work proposes an uncertainty-aware, multi-output, interpretable supervised machine learning (ML) framework to predict eight plasma parameters, viz. electron excitation temperature (Texc), electron number density (ne), four reactive species (OH, N2, Hα and O), gas temperature (Tg), and plume length. A dataset comprising 441 experimental runs was generated by varying the input powers (700-1000 W), sliding short positions (0.95-1.05λg/2) and argon flow rate (5-15 lpm). Six regression models, namely k-nearest neighbours (KNN), extra trees (ET), random forest (RF), artificial neural networks (ANN), gradient boosting (GB), and extreme gradient boosting (XGB), were optimized using Bayesian hyperparameter tuning and evaluated using both accuracy and reliability metrics. While XGB achieved competitive pointwise accuracy, the optimized GB model emerged as the most balanced performer when predictive accuracy, calibration behaviour, and uncertainty reliability were jointly considered. On a held-out test set, the GB model achieved mean absolute percentage errors below 3% and R2 values exceeding 0.97 across all plasma parameters. Bootstrap-based uncertainty quantification demonstrated near-nominal 90% prediction interval coverage with comparatively narrow uncertainty bounds, and calibration analysis confirmed statistically consistent uncertainty estimates. Experimental validation using 30 independent plasma operating conditions, separated into interpolated and extrapolated regimes, further confirmed robust generalization, with increased epistemic uncertainty appropriately accompanying extrapolative predictions. SHapley Additive exPlanations (SHAP) based interpretability analysis identified microwave power as the dominant controlling feature for most plasma parameters, while gas flow rate governed the intensity of OH emission. Overall, this uncertainty-aware ML framework provides a reliable foundation for data-driven plasma diagnostics and future optimization of MW-APPJ-based processes.

Abstract: In this work, we measure the plasma parameters by using an AC high-voltage power supply that generates a non-thermal plasma jet system at atmospheric pressure. A nickel (Ni) metal strip, with dimensions of 1.5 × 10 cm2, was connected to the anode electrode of the AC power supply. This nickel strip was immersed in a flask with a small amount of distilled water positioned below the plasma plume nozzle. Optical emission spectroscopy (OES) was used to diagnose the plasma system at different argon gas flow rates (1-5 L/min) and varying applied voltage values (11-15 kV). It is significant to know the processes accompanying plasma generation to measure their parameters which include the electron temperature (Te), electron number density (ne) of the plasma, Debye length (λD), and plasma frequency (fp). Our results showed an increase in the intensity of spectral lines with the increase in applied discharge voltage (11-15 kV). The maximum peak for ArI was observed at a wavelength of 811.531 nm, and the maximum peaks for nickel (Ni) were observed at wavelengths of 285.21 and 519.70 nm. Also, the results indicated a gradual increase in electron temperature (Te) and electron density (ne) values at the applied voltage of 0.403-0.468 eV. Likewise, the electron density (ne) was in the range of (11.486-13.851) × 1017 cm-3. Keywords: Atmospheric plasma jet, Nickel (Ni) plasma parameters, Electron temperature, Spectroscopic optical emission (OES).

This research presents a thorough spectroscopic investigation of atmospheric- plasma generated by a plasma jet. The study examines the plasma behavior under varying flow rates of argon gas. A primary objective is to identify the optimal flow rate that facilitates the application of the generated plasma in sterilization and bacterial eradication operations. The findings establish a correlation between argon flow and critical plasma parameters, specifically noting variations in electron temperature (Te) & electron number density (ne). Crucially, the study demonstrates that lower argon flow rates are more effective in generating active species such as hydroxyl and NO reactive species. The results of this investigation hold significant promise for advancing our comprehension of plasma jet technology's utility in sterilization or medical treatment processes, emphasizing the importance of gas flow optimization for these applications.

The non-equilibrium plasma jet at atmospheric pressure produces low-temperature plasma in an open environment, which has broad application prospects. Based on the emission spectrum of the argon plasma jet, this paper studies the variation of irradiance, electron temperature, electron density, and metastable particle number when the gas flow rate and axial distance are used as independent variables, respectively. The results show that with the increase in gas flow rate, the irradiance generally shows an increasing trend. At the same gas flow rate, the irradiance decreases with the increase of axial distance. With the increase of gas flow rate, the electron temperature decreases gradually, and the electron density increases gradually at the same axial distance. At the same gas flow rate, the electron temperature and electron density increase first and then decrease with the increase of axial distance. The number density of metastable particles increases with the increase of gas flow rate, and increases, decreases, and then increases with the increase of axial distance.

The arc discharge is directly related to the success of the current interrupting in switching apparatus in high-voltage electrical equipment. To diagnose the arc plasma, it is essential to use the Thomson scattering method which has better measurement accuracy and spatiotemporal resolution than other optical diagnostic methods. The laser Thomson scattering method has been widely used in diagnosing various plasmas in recent years because it does not rely on the local thermodynamic equilibrium (LTE) and the axial symmetry hypothesis. In this work, the arcing and arc decay processes of SF6 and N2 gas arcs were diagnosed using the Thomson scattering method, and a series of electron density evolution results were obtained. As time passes, the edges of the arc column in both the SF6 gas arc and N2 gas arc gradually reduce, leading to an overall decrease in electron number density. When compared with the N2 gas arc, the SF6 arc has a thinner arc column and a more extensive range of contraction during the arcing and decay processes. Furthermore, the SF6 arc has a lower electron number density, and its decay rate is faster at all times.

The microwave induced plasma jet (MIPJ) system was built using local materials and based on a tapered waveguide. The parameters of this plasma were determined like electron temperature Te, electron density ne. the other parameters such as plasma frequency( fp), the Debye length( λD), and the number of particles in the Debye sphere( Nd) It has also been studied. The study were done at different Ar flow rate ranging from (2-10) l/m and a discharge tube diameter ranging from (2-10) mm. all of these parameters were determined depending on the MIPJ spectrum. it turned out that there is a high possibility of controlling the parameters of MIPJ through manipulating these parameters.

This study aims to investigate the aluminum (Al) arc plasma parameters generated through the explosive strip technique. The research involves the measurement of key plasma characteristics such as plasma frequency (fp), Debye length, and Debye number. The electron temperature (Te) and electron density (ne) of the plasma were calculated utilizing the Boltzmann plot and Stark expansion method. Analysis of the optical emission spectrum revealed distinctive peaks corresponding to oxygen, Al, and zinc oxide (ZnO) within the plasma. The outcomes of the study demonstrated a noteworthy correlation between the applied current and the electron temperature and density. Specifically, as the current increases, both electron temperature and density increase. The electron temperature of the Al plasma increased from the range of 0.852 eV to 0.92404 eV, accompanied by a corresponding elevation in electron density from 13.1× 1017 cm-3 to 15.2× 1017 cm-3. Furthermore, the detonation of the Al strip within a ZnO suspension led to even more pronounced changes. In this case, the electron temperature surged from 0.92885 eV to 1.1012 eV, and the electron density experienced an increase from 37.7 × 1017 cm-3 to 44.7 × 1017 cm-3.

Laser interferometric measurements of the electron density of hypersonic plasma jets launched by a PJMIF-grade coaxial plasma gun newly developed at Shanghai Tech University. To validate the initial operating capability (IOC) of the Shanghai Tech Gun1 (STG1), A two-chord quadrature-heterodyne spatial optical interferometer is being used to make time-resolved density measurements of the hypersonic argon jet (Mach number M▫10). A CW 300-mW 532 nm laser with long coherence length (▫10 m) is adopted to relatively simplify optical layout without the need for matching reference and probe path lengths. An average Peak linear density of the order of $\sim 10^{18} \mathrm{~cm}^{-2}$ is observed, giving a total particle density of the order of $10^{17}$ per cc. A total jet mass of about 1 mg is estimated based on density profile. Jet density, velocity, mass and other factors are pivotal in quantifying and verifying the performance of the STG1 plasma gun.

No abstract available

Observing the light emission from plasmas spectroscopically allows for the determination of key plasma parameters like electron temperature, density and external field. This method, known as plasma spectroscopy, serves as a non-intrusive diagnostic tool to study plasma dynamics. However, overlooking the impact of radiation reabsorption in the typical analytic model may compromise the accuracy of observed plasma behavior. This study addresses the influence of radiation reabsorption on plasma spectroscopic diagnosis, focusing on linear divertor simulators and plasma spectrometers designed for high-density Large Helical Device (LHD) plasmas, where optical thickness cannot be disregarded. The discussion delves into understanding the effects of radiation reabsorption in these observations.

This work presents a comparative study of two diagnostic approaches for determining copper vapour admixtures in the thermal plasma of an electric arc discharge. The emission of plasma of arc discharge between copper electrodes was analysed using optical emission spectroscopy (OES) under discharge currents of 3.5 and 30 A. Two sets of plasma parameters were used as inputs for equilibrium composition calculations: (1) radial distributions of excitation temperature and copper atom number density, and (2) radial distributions of excitation temperature and electron density. The excitation temperature was determined using the Boltzmann plot technique, while electron density was obtained from spectral line broadening using Fabry-Pérot interferometer and by applying the Saha equation. The consistency of the calculated plasma compositions using both input sets demonstrates the applicability of indirect diagnostic methods for evaluating the erosion resistance of electrode materials.

The SF6/N2 gas mixture mitigates the challenges associated with the use and liquefaction problems of pure SF6. It has great significance to analyze the decay characteristics of the plasma in it. Laser-induced plasma (LIP) and gas arc represent two distinct types of plasma, differing significantly in energy density and duration. This study utilized collective Thomson scattering diagnostics to investigate the temporal and spatial evolution of electron density of these two plasmas, with varying SF6/N2 mix ratios as the gas medium. Our findings indicate that initially, the electron density in gas arc is lower, and its decay rate is generally slower compared to LIP. However, as the SF6 concentration increases, the decay process accelerates for both LIP and gas arcs. It is worth noting that when the SF6 volume fraction exceeds 70%, the decay rate of electron density approaches that of pure SF6 in both plasma types, suggesting a saturation effect near a 70% SF6/N2 mix ratio in terms of electron density decay.

Addressing the challenge of precise plasma density diagnostics in switching arcs, this study proposes a novel measurement approach based on two-color quadri-wave lateral shearing interferometry wavefront sensing. The developed 532/1064 nm dual-pulse laser system enables simultaneous high spatiotemporal resolution measurements of both electron and neutral particle densities in air arcs within a model circuit breaker. Experimental results show that during the arcing phase, the measured electron density in the arc core agrees well with local thermodynamic equilibrium (LTE) assumptions. In the post-arc free recovery phase without gas flow cooling, thermal inertia causes slow thermal recovery, with a 1 ms delayed rupture phenomenon observed in residual electron density channels. The measured density distribution during the decay process deviates from LTE predictions, demonstrating the need for non-equilibrium modeling. Compared with conventional interferometry, this method maintains high spatial resolution while offering superior advantages including strong anti-interference capability and simplified optical configuration through its common-path design. The method can be extended to arc density diagnostics in SF6 and its eco-friendly alternative gases, providing crucial experimental evidence for understanding non-equilibrium arc-quenching mechanisms and supporting the development of next-generation high-voltage switching devices.

Vacuum circuit-breakers (VCBs) are commonly used in emerging mechanical DC circuit-breakers. The electrical performance of VCBs in DC interruption duties has been extensively investigated, but basic physics such as the excitation temperature of plasma species, electron/vapor densities and emission of droplets in such applications were rarely reported. In this paper, we focus on how the short high frequency (HF) current pulse affects erosion of electrodes as well as generation of flying droplets by using laser shadow photography. Spectroscopy was adopted to obtain spectra and calculate the excitation temperature of CuI. Shack–Hartmann wavefront sensors were applied to measure neutral and electron density, in tests where di/dt, breaking current and the direction of the injected HF current varied. Indeed, the in-phase injection of the HF current caused an intense arc, but the pulse was too short to make either the cathode or anode melt. Since the plasma is in a nonequilibrium state, the excitation temperature of CuI is relatively low. Electron densities in different tests all approach similar values right before current zero. Neutral densities show strong fluctuation and independence on instantaneous current.

A gliding arc plasmatron (GAP) is a promising warm plasma source for the use in gas conversion applications but lacks an understanding of the plasma dynamics. In this paper, the gliding arc plasma conditions of a GAP operated with nitrogen flow (10 slm) are characterized using optical emission spectroscopy (OES) and numerical simulation. A simultaneously two-wavelength OES method and Abel inversion of the measured images with a spatial resolution of 19.6 μm are applied. The collisional radiative model used in this study includes Coulomb collisions of electrons. An iterative method of plasma parameter determination is applied. The determined values of the electric field up to 49 Td and electron density up to 2.5∙1015 cm−3 fit well to the plasma parameters received with different diagnostics methods in comparable plasma sources. Additionally, the electric current, which is calculated using the determined reduced electric field and electron density, is compared with the measured one.

No abstract available

The 3D evolution of key plasma parameters in a vacuum arc strongly affects the arc interrupting capacity of vacuum circuit breakers. However, traditional 3D diagnostics methods are typically based on the optically thin assumption, neglecting spectral broadening caused by the absorption effect. This limits accurate identification of internal radiation characteristics and spatial parameter distributions of the arc, thereby hindering the deeper understanding of arc evolution mechanisms. To address this issue, we proposed a 3D absorption correction algorithm considering spectral broadening. The algorithm first reconstructed the 3D emission coefficients of characteristic spectral lines at 510.6 nm and 515.3 nm using a tomography reconstruction method, and then calculated the upper-level atomic densities of characteristic spectral lines as well as the electron temperature. A modified collisional radiative model (CRM) was then employed to compute the electron density and population distribution, from which the line profiles and full width at half maximum (FWHM) were derived. Based on these parameters, the absorption coefficients and optical depth were obtained, and the Lambert–Beer law was applied to correct the radiation intensity. The results indicate that, after 3D absorption-corrected reconstruction with spectral broadening, the electron temperature, electron density, and atomic population in the axial magnetic field arc exhibit significant asymmetry. The peak electron temperature reaches 13 500 K, and the maximum electron density is 1.29 × 1023 m−3. Spectral broadening leads to a decrease in electron temperature, while its effect on electron density is minimal. In addition, the upper-level atomic densities are more sensitive to spectral broadening than those of the lower levels.

No abstract available

The process of plasma interaction with magnetic fields of an arch configuration plays a decisive role, for example, in coronal ejections in the sun or in the interaction of the solar wind with the Earth's magnetosphere. In this work, this process is simulated in laboratory conditions. The density of the plasma in the magnetic flow tube is determined by the vacuum arc discharge current, and the electrons are additionally heated under conditions of electron cyclotron resonance by the microwave radiation of the gyrotron. A technique for diagnostics and study of the characteristics of plasma flows is proposed. Test experiments were carried out, and a number of dependencies were obtained between the given parameters of the plasma flow density and electron cyclotron heating and the features of the plasma flow propagation.

No abstract available

No abstract available

No abstract available

No abstract available

No abstract available

We have used a tabletop soft-x-ray laser and a wave-front division interferometer to probe the plasma of a pinch discharge. A very compact capillary discharge-pumped Ne-like Ar laser emitting at 46.9 nm was combined with a wave division interferometer based on Lloyd's mirror and Sc-Si multilayer-coated optics to map the electron density in the cathode region of the discharge. This demonstration of the use of tabletop soft-x-ray laser in plasma interferometry could lead to the widespread use of these lasers in the diagnostics of dense plasmas.

No abstract available

As the importance of measuring electron density has become more significant in the material fabrication industry, various related plasma monitoring tools have been introduced. In this paper, the development of a microwave probe, called the measurement of lateral electron density (MOLE) probe, is reported. The basic properties of the MOLE probe are analyzed via three-dimensional electromagnetic wave simulation, with simulation results showing that the probe estimates electron density by measuring the surface wave resonance frequency from the reflection microwave frequency spectrum (S11). Furthermore, an experimental demonstration on a chamber wall measuring lateral electron density is conducted by comparing the developed probe with the cutoff probe, a precise electron density measurement tool. Based on both simulation and experiment results, the MOLE probe is shown to be a useful instrument to monitor lateral electron density.

The electrical conductivity is a key parameter affecting the characteristics of pulsed discharge. In the needle-needle electrode configuration, this article investigated the electrical and optical characteristics of underwater microsecond pulsed arc discharge with conductivities ranging from 390 to $2500~\mu $ S/cm. The effect of conductivity on average pre-breakdown delay and breakdown voltage was evaluated overall. For six typical discharge cases under different conductivities, a comparative analysis of discharge characteristics before and after gap breakdown was conducted. Higher conductivity resulted in increased conduction current and energy leakage during the pre-breakdown stage, thereby influencing the arc discharge stage. Images and emission spectra of the plasma channel under different conductivities were captured, the morphology of the arc channel was compared, and the time-varying characteristics of the electron density were diagnosed. The results demonstrated that the conductivity changed the energy deposition characteristics of the plasma channel, consequently affecting electron density.

This study outlines the development of a cost-effective power supply tailored for generating atmospheric pressure gliding arc discharge, primarily for non-thermal plasma processes. We conduct a comprehensive analysis of discharge characteristics using optical and electrical methods, focusing on parameters such as discharge temperature, plasma density, and current-voltage characteristics. The output voltage (VRMS) of the power supply increases within the range of (7.67±0.41) to (26.71±0.88) kV. Our findings indicate that arc velocity increases with the increase in airflow rate, whereas it is reduced with the increase in applied voltage. The power consumption of the discharge falls within 8.55–18.34 W for applied voltages ranging from 12.00 to 20.00 V. The electron temperature and density decrease toward the electrode outlet, with values of 1.194 ± 0.024 eV and (0.66±0.17)×1017 cm−3, respectively, at the outermost region. Variations in applied voltage affect both electron temperature and density. Additionally, airflow and applied voltage influence rotational and vibrational temperatures, with maximum values observed at the lowermost equilibrium position for increased airflow. Our findings demonstrate a non-thermodynamic equilibrium discharge, as evidenced by the fact that the electron temperature exceeds vibrational temperature and vibrational temperature exceeds rotational temperature. The suggested techniques are both practical and efficient, with a straightforward construction process, and have been demonstrated to be applicable in the agricultural field.

Arc discharge represents a significant failure of oil-immersed power transformers. The presence of an arc in the oil is often accompanied by optical radiation, heat generation, gas production, and vibration. The understanding of these phenomena is essential for the elucidation of the characteristics and mechanisms of arc discharges. In this paper, experimental simulations and emission spectral measurements of arcs in oil were carried out in order to elucidate the characteristics and mechanism of arcs. The radiation characteristics and variations were analyzed by statistical methods, and the physical parameters of the arc channel were calculated. The results indicate that the emission spectra of arcs in oil primarily originate from the transition of excited electrons, bremsstrahlung, and blackbody radiation. The electron excitation temperature and electron density of the arc channels are calculated from the spectral lines of hydrogen, which are about 4000K and 1017/cm−3, respectively.

In this paper, the Magnetically Stabilized Gliding Arc Discharge (MSGAD) system was constructed to produce non-thermal plasma using argon gas under atmospheric pressure. A gliding plasma discharge was stabilized by a magnetic field for the purpose of a planned investigation. The emission spectra of the generated plasma using a gliding arc discharge system were recorded under atmospheric pressure, with a constant value of alternating voltage (4 kV) and at different gas flow rates of) 0.5–2.5 (L/min. The plasma parameters, including electron temperature (Te), electron density (ne), plasma frequency, Debye length and electron temperature, were calculated. The electron temperature was measured using the Boltzmann plot method, and the electron density was determined using the Stark broadening method. The results show an increase of the electron temperature from 1.138 to 1.277eV and electron density from 2.78×1017 to 3.48×1017 cm-3 as the gas flow increased from 0.5 to 2.5 L/min. Also, the spectral line intensity increases with the increase of the gas flow rate.

No abstract available

The paper presents the results of studies of non-self-sustained arc discharge in zirconium vapors. The method of initiating a vacuum arc discharge is described. Its main characteristics are given. The influence of the external magnetic field on the characteristics of the discharge and generated plasma flows is shown. The values of the plasma potential in the flows are determined. It was found that the anodic potential drop in the discharge has a positive value and decreases with grows of the discharge current. The values of the electron temperature, plasma density and floating potential in the generated flows of the zirconium vapor plasma were determined. Data on the growth rate of deposited films are given and it is shown that the ionization coefficient in plasma flows is (60-90) % at various currents of the discharge.

The vacuum arc discharge makes transition to a footpoint mode, anode spot type 1 (type 1) mode and anode spot type 2 (type 2) mode under high current conditions. The mode dependence of the electron and metal vapor densities were experimentally quantified using dichroic Shack–Hartmann type laser wavefront sensors. In the type 1 mode, the electron and metal vapor densities were about 2.5 times higher than the footpoint mode. The electron density of the type 2 mode was three times higher than that of the type 1 mode, while significant difference was not found in the metal vapor density. Such higher electron density for the type 2 mode than the type 1 mode was coherent with a previous result obtained by Stark broadening. The present electron and metal vapor density measurement demonstrated that the amount of the electrode erosion was in the following order: footpoint mode < type 1 mode < type 2 mode, which agreed with a previous study.

The research on generation and propagation of large-radius low-energy (up to 10 keV) electron beam with millisecond pulse duration by the plasma-cathode electron source in the forevacuum pressure range (3–30 Pa) is presented. An arc discharge with cathode spot has been used to generate emission plasma with millisecond pulse duration. Large hollow anode and ball-shaped redistributing electrode have provided formation of arc plasma with emission surface of 100 cm2; emission plasma boundary has stabilized by metallic mesh. It is established, that gas type and gas pressure affect the parameters of the arc discharge. In case of gases with greater ionization cross section (argon, nitrogen), an increase of gas pressure has led to a decrease of arc voltage and to an increase of emission plasma density. Gas with small ionization cross section (helium) had weak effect on the arc discharge parameters. An increase of emission window in the anode has provided an increase in radius of the electron beam and an increase of efficiency of electron extraction from the arc plasma; on the other hand it has led to an increase of influence of back-streaming ion flow on the electron emission and led to a decrease of maximal operating gas pressure. Reducing the geometric transparency of the emission mesh, as well as the use of gas with small ionization cross section have provided an increase in the maximal operating pressure of the source of large-radius electron beam. It is established, that in the forevacuum pressure range, large-radius electron beam is efficiently generated in the investigated range of distances from the extractor up to 35 cm.

Pin-pin discharge between bare electrodes is one of the most classic and simplest discharge generated under atmospheric air, and it has widely applications depending on its various discharge modes, such as streamer discharge in ozone generation, glow discharge in elemental analysis, and spark discharge in nitrogen fixation. In this study, we controlled the pin-pin discharge transiting from streamer mode, to glow mode and arc mode, by matching a group of resistor and capacitor under the excitation of AC high- voltage. Besides, the spark mode of pin-pin discharge was also generated under the excitation of nanosecond pulse. The breakdown and evolution process of discharge were investigated by ICCD and streak camera. It is found that discharge mode of glow, arc or spark are all transformation from the initial streamer. The fast breakdown of initial streamer discharge is about 1.25 ns, and there is a bright cathode spot existed before the discharge transition. Last but not least, the electron density, excitation temperature, vibrational temperature, rotational temperature are diagnosed to understand the characteristics of various discharge modes.

Computational model of high-current pulsed arc discharge in air is proposed. This is, in general, two-dimensional model with taking into account gas dynamics of the discharge channel, real air thermodynamics in a wide range of pressure and temperature, electrodynamics of the discharge including pinch effect, and radiation. The developed model was applied to simulate the electric discharge in air for the currents of 1 - 250 kA and characteristic rise times in 13 - 25 µs, and results of calculations were compared with experimental ones. It was concluded that most of characteristics of the discharge are predicted well. Namely, arc column radius and shock wave position agree well with experimental data for all current amplitudes and rise times considered. Radial distributions of temperature and electron density also satisfactorily agree with experimental data. It was found that pinch effect should be considered for currents higher than 100 kA.

A global integral model of an arc discharge in helium with sputtered composite metal-graphite anode is presented. The arcing time was measured experimentally for different elements and mass fractions of the metal additions to the graphite anode. The obtained calculated results for pure graphite anode show a good agreement with the experimental and calculated data of other authors. In particular, a good correspondence between the absolute values of electron density and temperature, the discharge voltage and the anode ablation rate as a function of the discharge current was shown. The obtained in the work experimental and calculated data have qualitative agreement, i.e. the anode erosion velocity increases with the addition of Zr, and decreases with the addition of Al.

No abstract available

A global integral model of an arc discharge in a helium medium with a sputtered graphite anode is presented. The main feature of the model is the simultaneous consideration of the plasma of the discharge gap, the cathode and anode layers, the current transfer, the thermal regime of the electrodes, and the evaporation of the anode. Both the calculated and experimental results show that the discharge voltage linearly increases with the inter-electrode distance, as in a classical positive column where the voltage drop is proportional to its length with a constant electric field. The calculated data also show a good agreement with the experimental and calculated data of other authors, in particular, a good correspondence between the absolute values of electron density and temperature, the discharge voltage and the anode ablation rate as a function of the discharge current.

No abstract available

In this study, the process of electrolytic–plasma nitrocarburizing (EPNC) of 20-grade steel was investigated using various electrolytes and temperature regimes. At the first stage, optical spectral analysis of plasma emission during EPNC was carried out with spectral registration in the range of 275–850 nm, which allowed the identification of active components (Hα, CN, Fe I, O I lines, etc.) and the calculation of electron density. Additionally, the EPNC process was recorded using a high-speed camera (1500 frames per second), which made it possible to visually evaluate the dynamics of arc and glow discharges under varying electrolyte compositions. At the next stage, the influence of temperature regimes (650 °C, 750 °C, and 850 °C) on the formation of the hardened layer was studied. Using SEM and EDS methods, the morphology, phase zones, and the distribution of chemical elements were determined. Microhardness measurements along the depth and friction tests were carried out. It was found that a temperature of 750 °C provides the best balance between the uniformity of chemical composition, high microhardness (~800 HV), and a minimal coefficient of friction (~0.48). The obtained results confirm the potential of the selected EPNC regime for improving the performance characteristics of 20-grade steel.

Coaxial plasma guns are a type of plasma source that produces plasma which propagates radially and axially controlled by the shape of the ground electrode, which has attracted much interest in several applications. In this work, a 120° opening angle of CPG nozzle is used as a plasma gun configuration that operates at the energy of 150 J. The ionization of polyethylene insulator between the electrodes of the gun produces a cloud of hydrogen and carbon plasma. The triple Langmuir probe and Faraday cup are used to measure plasma density and plasma temperature. These methods are used to measure the on-axis and off-axis plasma divergence of the coaxial plasma gun. The peak values of ion densities measured at a distance of 25 mm on-axis from the plasma gun are (1.6 0.5) 10 m and (2.8 0.6) 10 m for hydrogen and carbon plasma respectively and the peak temperature is 3.02 0.5 eV. The mean propagation velocity of plasma is calculated using the transit times of plasma at different distances from the plasma gun and is found to be 4.54 0.25 cm/ s and 1.81 0.18 cm/ s for hydrogen and carbon plasma respectively. The Debye radius is obtained from the measured experimental data that satisfies the thin sheath approximation. The shot-to-shot stability of plasma parameters facilitates the use of plasma guns in laboratory experiments. These types of plasma sources can be used in many applications like plasma opening switches, plasma devices, and as plasma sources.

A lossy-mode resonance optical fiber sensor operating as an electro-optical transducer for analysis of ionized gas media, such as plasma, is introduced. Comparison of the sensor performance with an electrical Langmuir probe is discussed.

Current inference techniques for processing multi‐needle Langmuir probe (m‐NLP) data are often based on adaptations of the Orbital Motion‐Limited (OML) theory which relies on several simplifying assumptions. Some of these assumptions, however, are typically not well satisfied in actual experimental conditions, thus leading to uncontrolled uncertainties in inferred plasma parameters. In order to remedy this difficulty, three‐dimensional kinetic particle in cell simulations are used to construct a synthetic data set, which is used to compare and assess different m‐NLP inference techniques. Using a synthetic data set, regression‐based models capable of inferring electron density and satellite potentials from 4‐tuples of currents collected with fixed‐bias needle probes similar to those on the NorSat‐1 satellite, are trained and validated. The regression techniques presented show promising results for plasma density inferences with RMS relative errors less than 20%, and satellite potential inferences with RMS errors less than 0.2 V for potentials ranging from −6 to −1 V. The new inference approaches presented are applied to NorSat‐1 data, and compared with existing state‐of‐the‐art inference techniques.

To identify the discharge features of tungsten inert gas (TIG) welding arc on magnesium alloy workpiece, spectral diagnosing and a self-developed Langmuir probe detection were jointly performed on the welding arc. Results show that during welding, Mg atoms with low ionization energy rush into the burning arc and replace Ar atoms to discharge, which gives influences on arc discharge. The arc plasmas have a normal space potential distribution. Reflected by both of the two diagnosing methods, region near arc anode (magnesium alloy workpiece) has the lowest electron temperature and the highest electron density. The variations of electron temperature and density with the position have similar trends measured by the two diagnosing methods, indicating that the self-developed probe detection system is effective and reliable in diagnosing the welding arc. It is also found that the diagnosing error of probe detection is a little larger than that of spectral diagnosing, especially in the region near cathode. This research gives a new method to diagnose the welding arc, and the results can give experimental indication and support to researchers in arc welding area from another view sight.

No abstract available

This work describes the application of Langmuir probe diagnostics to the measurement of the electron temperature in a time-fluctuating-highly ionized, non-equilibrium cutting arc. The electron retarding part of the time-averaged current-voltage characteristic of the probe was analysed, assuming that the standard exponential expression describing the electron current to the probe in collision-free plasmas can be applied under the investigated conditions. A procedure is described which allows the determination of the errors introduced in time-averaged probe data due to small-amplitude plasma fluctuations. It was found that the experimental points can be gathered into two well defined groups allowing defining two quite different averaged electron temperature values. In the low-current region the averaged characteristic was not significantly disturbed by the fluctuations and can reliably be used to obtain the actual value of the averaged electron temperature. In particular, an averaged electron temperature of 0.98 ± 0.07 eV (= 11400 ± 800 K) was found for the central core of the arc (30 A) at 3.5 mm downstream from the nozzle exit. This average included not only a time-average over the time fluctuations but also a spatial-average along the probe collecting length. The fitting of the high-current region of the characteristic using such electron temperature value together with the corrections given by the fluctuation analysis showed a relevant departure of local thermal equilibrium in the arc core.

The plasma-beam boundary is the main focus of the negative ion source study. The boundary behavior affects negative ion beam formation throughout the negative ion neutral beam injector. Simulation for optimizing the beam profile is under development and shows different results from experimental data. For this reason, experimental results from the region are valuable for constructing theory and as a guide for simulation development. This paper shows space potential and density measurement with a Langmuir probe scanning inside the extraction aperture. The density measurement shows the movement of plasma according to the arc power, magnetic field, and applied extraction field.

In the electron source with a grid plasma cathode based on a low-pressure arc discharge, the parameters of the emission plasma were investigated depending on the different conditions of its generation (type of gas, operating pressure, discharge current amplitude, resistance in the hollow anode circuit of a plasma emitter). For this purpose, a single cylindrical Langmuir probe was used. To measure the current-voltage characteristics of the probe, taking into account the features of the functioning of the electron source (galvanic isolation from high accelerating voltage, the use of high-voltage cables with high parasitic parameters, etc.), an automated measurement circuit was used, allowing for a relatively short time to collect high statistics of experimental data (depending on the frequency the impulses of the discharge current and their total number). To eliminate the influence of the parasitic parameters of the circuit, the measurement circuit was located in the maximum proximity to the generation space of the emission plasma (in a vacuum chamber), which significantly increased the accuracy of the experimental data obtained.

No abstract available

Researches on plasma-facing materials/components (PFMs/PFCs) have become a focus in magnetic confinement fusion studies, particularly for advanced tokamak operation scenarios. Similarly, spacecraft surface materials must maintain stable performance under relatively high temperatures and other harsh plasma conditions, making studies of their thermal and ablation resistance critical. Recently, a low-cost, low-energy-storage for superconducting magnets, and compact linear device, HIT-PSI, has been designed and constructed at Harbin Institute of Technology (HIT) to investigate the interaction between stable high heat flux plasma and PFMs/PFCs in scrape-off-layer (SOL) and divertor regions, as well as spacecraft surface materials. The parameters of the argon plasma beam of HIT-PSI are diagnosed using a water-cooled planar Langmuir probe and emission spectroscopy. As magnetic field rises to 2 T, the argon plasma beam generated by a cascaded arc source achieves high density exceeding 1.2×1021 m−3 at a distance of 25 cm from the source with electron temperature surpassing 4 eV, where the particle flux reaches 1024 m−2s−1, and the heat flux loaded on the graphite target measured by infrared camera reaches 4 MW/m2. Combined with probe and emission spectroscopy data, the transport characteristics of the argon plasma beam are analyzed.

No abstract available

Precisely assessing plasma parameters holds paramount importance in investigating the arc extinguishing mechanism of semi-sealed splitter plate DC circuit breakers, refining the configuration of splitter plates, and optimizing the overall structural design of circuit breakers. Based on the principle of the Langmuir probe, a double probe diagnostic method is proposed to investigate the air arc plasma in the opening process of a DC circuit breaker. The diagnostic circuit of the probes is designed, and three sets of double probes are arranged to trace the evolution of the plasma density during the opening process. The research reveals that the plasma center density, measured by the diagnostic system during the opening process of the DC circuit breaker, is about 1022 m−3–1023 m−3. This density is compared with the diagnostic results obtained by other methods, confirming the accuracy of the Langmuir double probe for plasma measurements in the DC circuit breaker. The study also revealed an exponential decay behavior of electron density along the radial direction of the arc. A mathematical model was employed to describe this phenomenon, establishing a relationship between the distribution of electron density and arc current.

A Langmuir probe array consisting of several Langmuir probes made of different refractory materials is developed to study the influence of different probe materials on plasma diagnostic results. Diagnosis of argon plasmas with different discharge powers is accomplished using the Langmuir probe array together with an emissive probe. Standard results of plasma parameters are considered to be those obtained by using the hot probe with zero emission limit method. Compared with the standard results, the plasma parameters obtained by the Langmuir probes made of platinum and rhenium are basically consistent with the standard results, indicating that they are excellent materials for making Langmuir probes. In addition, the plasma parameters obtained by the Langmuir probes made of nickel and tantalum are underestimated by slightly more than 10%, suggesting that they are not suitable for use as Langmuir probes compared to other refractory metals.

No abstract available

ABSTRACT Ionization processes in chemically reacting systems attract much attention from researchers as one of the ways to create low-temperature plasma. Reliable quantitative diagnostics, i.e. determining the absolute concentrations of charged particles (ions and electrons) and their collisions frequencies with neutral components in low-temperature plasma with reactions of chemical ionization, is also of great interest. One of the most direct methods for determining the concentration of free electrons is the microwave interferometry technique. In the current paper, we carried out kinetic modeling of the formation of free electrons in the process of chemical ionization during the oxidation of various hydrocarbons, in particular methane, acetylene, ethylene and propane in reflected shock waves. The simulated profiles of the concentration of free electrons for methane and acetylene were compared with the results of our own experiments carried out using a microwave interferometer, and their good agreement was obtained. We also compared the results of our kinetic simulations with the results of experiments on a microwave interferometer of a different design carried out by other authors for chemical ionization of a number of aliphatic hydrocarbons such as methane, acetylene, ethylene and propane.

Flash x-ray radiography is an important diagnostic in hydrodynamic experiments to provide fluoroscopic imaging of fast-moving dense targets. In order to obtain multiple images of an object at different times in an experiment, a flash x-ray accelerator is required to output multiple pulses. For the induction voltage adder (IVA) multi-pulse accelerator, it is important to study the effect of the cathode plasma generated by the front pulse in magnetically insulated transmission lines (MITLs) on the transmission of the subsequent pulses. In this paper, a coaxial MITL experimental platform based on the “QiangGuang-I” accelerator is established to study the dissipation characteristics of the cathode plasma, and its working condition is similar to that of MITLs in typical IVA accelerators. In the experiment, a stable magnetic insulation is formed in the coaxial MITL, and the current loss along the line can be ignored. The microwave interferometer is used to measure the evolution of cathode plasma density over time for hundreds of microseconds after the pulse disappears. The measurement results of microwave interference show that the line-averaged density of the plasma in the anode–cathode gap is above 1 × 1018 m−3, and the time for the plasma density to decrease to 1 × 1016 m−3 is about 600 μs. The expansion velocity of the plasma after a pulse is much lower than that during the pulse. In addition, the dissipation characteristics of the cathode plasma with different electrical parameters of the pulses are compared and analyzed.

A type of gas discharge, defined as a gliding arc-microwave hybrid discharge (also called microwave-enhanced gliding arc discharge or gliding arc-assisted microwave discharge), is proposed, and its coordination effects for generating plasma are experimentally investigated. The gliding arc acts as an igniter for generating and maintaining the microwave plasma at atmospheric pressure, while the microwave has a certain effect on expanding the gliding arc plasma. The increase in voltage and power observed in the microwave-enhanced gliding arc discharge indicates expansion of length and bulk of the plasma flame, which has a positive effect on the residence time and immersion of reactants in the plasma. The presented hybrid discharge can be applied to different fields such as chemical synthesis, surface treatment, and fuel reforming, as it can generate efficient quasi-thermal plasma with reaction selectivity.

No abstract available

Microwave interferometry is a reliable, well established, and non-perturbing method to measure the line-integrated electron density of a non-uniform plasma through the phase shift of a wave that propagates the plasma medium. In this paper we combine the phase shift and the attenuation of the wave to experimentally extract both, the line-integrated density and the electron–neutral collision frequency of an atmospheric plasma torch. In addition, a novel method to obtain the 2D spatial plasma density profile of the torch is demonstrated by measuring the microwave power, without any information of the phase. The receiving antenna of the interferometer is moved perpendicularly to the axis of the torch and measures the spatial distribution of the microwave power. The wave is scattered by the plasma and the scattering profile depends on the plasma density profile. Direct comparison of this scattering profile with 3D full-wave simulations provides information on the electron number density profile of the plasma torch.

Microwave interferometry (MWI) is a nonintrusive diagnostic technique, capable of measuring small quantities of electrons present in a flame plasma. In this paper, a 94 GHz microwave interferometer is characterized and validated to perform robust and reliable measurements of electron concentrations in thermal and nonthermal plasmas in a shock tube. The MWI system is validated first by measuring the refractive index of a dielectric material. Subsequently, the system is used for measuring electron densities during the thermal ionization of argon and krypton in shock tube experiments. The measured activation energies are in good agreement with both the measured values from previous studies and theoretical values. The MWI system is finally used for measuring electron density time-histories in fuel oxidation experiments in the shock tube. The electron density profile of methane combustion shows a peak at the ignition time which agrees with pressure measurements. Experimental electron histories are also in overall agreement with predictions of the methane ion chemistry model.

No abstract available

No abstract available

A laboratory-scale experiment was conducted to reproduce plasma with properties similar to re-entry plasma and measure the plasma density using a microwave reflectometer system. To reproduce a similar re-entry plasma, a high-temperature refractory anode vacuum arc plasma method was used among arc plasma discharge methods, and arc plasma having high temperature, high speed, and high-density plasma characteristics was discharged inside a vacuum chamber. A hot refractory anode made of tungsten was used to show high-temperature plasma characteristics, and high-density plasma characteristics were demonstrated using re-evaporation around the anode. In addition, high-speed plasma characteristics were exhibited using a brass cathode. This kind of arc plasma discharge has a high temperature and is characterized by high fluctuation. It was determined that a microwave reflectometer system with good spatial resolution and non-invasiveness would be suitable to measure plasma with these characteristics. The reflection coefficient was measured using a reflector system by comparing the voltage between the traveling wave applied to the plasma and the reflected wave reflected by the plasma, and the technique of analyzing the plasma density using the difference between these reflection coefficients was used. In this study, the plasma density according to the pressure change was typically measured as 1012-1013 cm-3, which showed a similar tendency to the result of measuring the actual re-entry plasma density.

To investigate the behavior of plasma generated in the shock tube, microwave reflectometry is proposed to extract the permittivity <inline-formula> <tex-math notation="LaTeX">$\epsilon _{r}$ </tex-math></inline-formula> of plasma. To remove the influence of parasitic reflections caused by the surroundings, a calibration process is introduced and the unknown calibration coefficients are determined by utilizing microwave interferometry as the reference technique. The shock tube is modeled as a three-layered medium to calculate the reflection coefficient. A time-dependent reconstruction algorithm is applied and theoretically validated to eliminate the multiple solutions in the inverse problem. By comparing the permittivities extracted with microwave reflectometry and interferometry, the effects of plasma diffusion are demonstrated with a modified analytical model in the beginning time region of experiments. In addition, the nonuniform flow in the generated plasma located near the end time region is also observed. The determination of the effective time region for electron density <inline-formula> <tex-math notation="LaTeX">$N_{e}$ </tex-math></inline-formula> and collision frequency <inline-formula> <tex-math notation="LaTeX">$v_{e}$ </tex-math></inline-formula> extraction is discussed as well. Finally, the differences between microwave reflectometry and interferometry in terms of averaged <inline-formula> <tex-math notation="LaTeX">$N_{e}$ </tex-math></inline-formula> < <inline-formula> <tex-math notation="LaTeX">$1{\times }10^{17} m^{-3}$ </tex-math></inline-formula> and averaged <inline-formula> <tex-math notation="LaTeX">$v_{e}$ </tex-math></inline-formula> < <inline-formula> <tex-math notation="LaTeX">$1.5{\times }10^{9} s^{-1}$ </tex-math></inline-formula> are investigated in the effective time region

In this study, a plasma diagnostic system based on linear frequency-modulated continuous wave (LFMCW) is designed to calculate the electron density by determining the change of electromagnetic wave propagation time delay. The system adopts a swept microwave interferometry method to accurately measure the effect of plasma on the propagation time delay and solves the problem of phase-periodic ambiguity in the traditional microwave diagnostic method. This article describes the system design, including hardware selection, signal processing flow, and system simulation. Experiments show that the system can effectively diagnose high electron density plasma.

The note presents the first plasma density measurements collected by a novel microwave interferometer in a compact Electron Cyclotron Resonance Ion Sources (ECRIS). The developed K-band (18.5 ÷ 26.5 GHz) microwave interferometry, based on the Frequency-Modulated Continuous-Wave method, has been able to discriminate the plasma signal from the spurious components due to the reflections at the plasma chamber walls, when working in the extreme unfavorable condition λp ≃ Lp ≃ Lc (λp, Lp, and Lc being the probing signal wavelength, the plasma dimension and the plasma chamber length, respectively). The note describes the experimental procedure when probing a high density plasma (ne > 1 ⋅ 1018 cm-3) produced by an ECRIS prototype operating at 3.75 GHz.

The Electron Cyclotron Resonance Ion Sources (ECRISs) development is strictly related to the availability of new diagnostic tools, as the existing ones are not adequate to such compact machines and to their plasma characteristics. Microwave interferometry is a non-invasive method for plasma diagnostics and represents the best candidate for plasma density measurement in hostile environment. Interferometry in ECRISs is a challenging task mainly due to their compact size. The typical density of ECR plasmas is in the range 10(11)-10(13) cm(-3) and it needs a probing beam wavelength of the order of few centimetres, comparable to the chamber radius. The paper describes the design of a microwave interferometer developed at the LNS-INFN laboratories based on the so-called "frequency sweep" method to filter out the multipath contribution in the detected signals. The measurement technique and the preliminary results (calibration) obtained during the experimental tests will be presented.

No abstract available

The calculation of ray tracing for microwaves at 36 GHz frequency depending on the different maximum values of density was made. The calculation showed when rays hit or do not hit into the horn antenna shifted at angle 60° degrees with respect to the axis of the radiating horn antenna. In addition, the calculated and experimental measurements of the phase shift dependence in time for the through and inclined probing were performed. The use of refraction during interferometry can give additional information about plasma when the through probing interferometry is impossible.

No abstract available

The formation of a plasma sheath on the surface of spacecraft or satellites during high-speed atmospheric entry is a significant factor that affects communication and radar detection. Experimental research apparatus for electromagnetic science can simulate this plasma sheath and study the interaction mechanisms between electromagnetic waves and plasma sheaths. Electron density is a crucial parameter for this research. Therefore, in this paper, a HCN heterodyne interferometer has been designed to measure the electron densities of the device, which range from 1 × 109 to 3 × 1013 cm-3 and the pressure ranges from 50 to 1500 Pa. The light source is a HCN laser with a wavelength of 337 µm, which exhibits higher spatial resolution compared to microwave interferometers. The interferometer is configured as a Mach-Zehnder interferometer, which generates an intermediate frequency through the Doppler shift achieved by a rotating grating. The spatial and temporal resolution of the HCN interferometry reach ∼14 mm and 100 µs, respectively. Antenna-coupled ALGaN/GaN-HEMT detectors have been utilized, as they possess higher sensitivity-with a typical reduction factor responsivity of around 900 V/W-than VDI planar-diode Integrated Conical Horn Fundamental Mixers in HCN interferometry. Recently, the initial results of the HCN interferometer designed for ERAES have been obtained during an experimental campaign, demonstrating a phase resolution of up to 0.04π.

The basic properties of a Talbot interferometer implementing pinhole arrays were experimentally and numerically investigated for the improvement of measurement sensitivity of laser wavefront sensors utilized for electron density imaging over discharge plasmas. A numerical simulation using a plane wave decomposition method indicated that the pinhole arrays with a pitch of 300 μm and a pinhole diameter of 150 μm were most suitable for the measurement of the millimetre-scale discharge plasmas, in consideration of the spatial resolution and measurement accuracy. The plane wave decomposition simulation expected that the measurement sensitivity of the 8th-Talbot-length interferometer could be improved by a factor of 4 compared with the previously developed Shack-Hartmann type laser wavefront sensors, which was experimentally verified by the self-image behavior of the pinhole arrays. The Talbot interferometric system was successfully used for electron density imaging over the vacuum arcs generated between a 3-mm gap. The electron density image observed by the Talbot interferometers was in excellent agreement with that visualized by the previously developed Shack-Hartmann sensors. The practical notification for the pinhole array fabrication was also presented.

The European Shock Tube for High-Enthalpy Research is a new state-of-the-art facility, tailored for the reproduction of spacecraft planetary entries in support of future European exploration missions, developed by an international consortium led by Instituto de Plasmas e Fusão Nuclear and funded by the European Space Agency. Deployed state-of-the-art diagnostics include vacuum-ultraviolet to ultraviolet, visible, and mid-infrared optical spectroscopy setups, and a microwave interferometry setup. This work examines the specifications and requirements for high-speed flow measurements, and discusses the design choices for the main diagnostics. The spectroscopy setup covers a spectral window between 120 and 5000 nm, and the microwave interferometer can measure electron densities up to 1.5 × 1020 electrons/m3. The main design drivers and technological choices derived from the requirements are discussed in detail herein.

To overcome the challenges associated with diagnosing electron density distributions in high-temperature plasma environments, a novel diagnostic method is proposed that integrates Langmuir probe measurements with hydrogen cyanide (HCN) laser interferometry. This technique is applied to the experimental apparatus for plasma-electromagnetic science of near-space hypersonic targets (EAPEHT). The Langmuir probe is used to measure the radial electron temperature, from which the electron density profile is derived based on the ion saturation current. Simultaneously, the HCN laser interferometer provides line-averaged electron density measurements, which are employed to calibrate and refine the probe-based results. Compared with conventional Langmuir probe techniques, the proposed method enhances diagnostic accuracy while reducing the number of required spatial measurements. Experimental results indicate strong agreement with traditional probe diagnostics, with relative deviations within the range of 10%–20%. Furthermore, the radial electron density distribution exhibits a Gaussian profile, validating the reliability and effectiveness of the proposed diagnostic approach.

It is difficult to diagnose the electron density of a high-temperature ablation plasma flow field because a traditional cylindrical Langmuir probe (CP) is easily damaged under these conditions. In this work, a new type of embedded Langmuir probe, referred to as a double flush-mounted probe (DFP), was developed to measure the electron density of a high-temperature ablation plasma flow field. It was verified that the DFP can work stably in different types of wind tunnels. In addition, the results from the new probe were compared with those from a CP. The results suggest that the DFP can be used to accurately determine the plasma density over long time periods. Therefore, this work provides a feasible method for solving the problem of online diagnostics in a high-temperature ablation plasma flow field.

A plasma sheath will be generated around the hypersonic vehicle during reentry, where a large number of electrons will significantly affect the propagation of EM waves, resulting in the phenomenon of communication blackout. This paper proposes a method of reducing the electron density of reentry vehicle plasma sheath by pulsed discharge. Experiments were conducted in a high-speed plasma wind tunnel to study the effects and scope of pulsed discharge on the plasma sheath electron density using an ultrahigh-speed camera and microwave diagnostic system. The experimental results show that the application of pulsed discharge resulted in the formation of a light intensity attenuation region measuring 14 × 19 × 4 cm around the discharge area, with an attenuation degree ranging from 30% to 58%. The microwave diagnostic results indicate that after the actuator discharge, the electron density of the plasma sheath within a 4 cm height above the vehicle wall is significantly reduced compared to before the actuator discharge, with a maximum reduction of approximately 86%. These results demonstrate that this method has significant effects on reducing plasma sheath electron density. Furthermore, the low power consumption, load, and space requirements suggest that it has potential for practical applications.

In this paper, a single probe (SP) has been designed for study plasma parameters of High enthalpy ICP-heated wind tunnel. It is found that the electron temperature in the core region is about 2.4 eV and that in the edge region is about 3–4 eV. At the maximum power of the High Enthalpy ICP-heated wind tunnel, the electron density reach 4.34 × 1013 cm-3. Meanwhile, the radial electron density distribution of SP is numerically integrated to calculate the line integral density, which is compared with the line integral density measured by 890 GHz HCN laser interferometer. The results show that the probe diagnosis results have the same trend as the laser diagnosis results. The line integral electron density measured by SP is 0.8 times higher than that measured by the HCN interferometer.

Pulsed discharge can generate high density and high dynamic plasma, which has promising application prospects in the field of stealth technology for high-speed aircraft. To study the evolution process of pulsed discharge plasma jet in a hypersonic flow field, the pulsed discharge experiment was performed in a hypersonic wind tunnel with 8 M in this paper. The plasma evolution process and electron density were measured by a high-speed schlieren device and spectrum acquisition system. A shock wave appeared after the blast wave generated by the discharge interacted with the external flow field. In the region below the shock wave, the plasma jet flowed downstream and produced a plasma layer. The electron density of the jet increases with the injected energy, and the peak density reaches 5.28 × 1015 cm−3. Due to the limitations of experimental measurements, based on the Navier–Stokes equations and the air dissociation and ionization model, including 11 components and 20 chemical reactions, a simulation for the experimental process was performed. At the injected energy of 495 and 880 mJ, the difference between the simulated electron density and the experimental value is 16.09% and 15.34%, respectively. The thickness of the plasma layer initially increases and then decreases over time, with higher injected energy leading to a thicker layer. Specifically, when 880 mJ of energy is injected, the plasma layer can reach a maximum thickness of 6.69 cm. The collision frequency fluctuates around 1 GHz, and the collision frequency at the upper edge of the plasma layer is large.

Communication blackouts during atmospheric reentry pose significant challenges to the safety and adaptability of spacecraft missions. This phenomenon, caused by the attenuation of electromagnetic waves by the plasma surrounding the spacecraft, disrupts communication with ground stations or orbiting satellites. Therefore, it is crucial to decrease the plasma density in the vicinity of the spacecraft to ensure an unobstructed electromagnetic wave communication path. This study proposes a methodology that involves the injection of gas from the vehicle’s wall to create an insulating layer near the surface. This thin layer maintains lower temperatures and reduced plasma density, enabling electromagnetic wave propagation without attenuation. Practical experiments were conducted in an arc-heating facility to simulate atmospheric reentry conditions. The results of the experiments provided empirical evidence of the effectiveness of the technique in mitigating communication blackout phenomena. Numerical fluid analysis within the wind tunnel chamber validated the formation of an air film layer near the experimental model owing to the injected gas. Schlieren imaging revealed distinctive jet shapes, which corroborated the findings of the numerical analysis. The wind tunnel tests that simulated atmospheric reentry environments confirmed the formation of an air film layer through gas injection, which substantiates the reduction in communication blackout. These results have the potential to improve communication reliability in space transport.

Chemical kinetic schemes have been developed for hypersonic flows with ablative carbon and carbonaceous components; however, experimental data for the validation of these schemes are limited. Therefore, in this study, we use a carbon-ablation chemical kinetics model to identify changes in the refractive index field near a hypersonic vehicle as well as other experimentally observable metrics that can be detected in future experiments conducted in a high-enthalpy wind tunnel. The combined use of a zero-dimensional kinetics model, two-dimensional hypersonic flow simulations, and a refractive index model confirm that the level of carbon present in Mach 24 hypersonic flow significantly affects the refractive index, electron density, and shock wave location. All three metrics can be used for an analysis of ablation products in a high-enthalpy wind tunnel.

Communication blackouts during the atmospheric reentry phase are a significant challenge, as flight data are lost due to interruptions caused by plasma gas generated by aerodynamic heating. This study explores a novel mitigation method using an air film, a thin insulating coolant layer on the surface. The researchers successfully reduced the reentry blackout by employing a gas injection system. Through a coupled approach using computational fluid dynamics and a frequency-dependent finite-difference time-domain method, the plasma flow properties and electromagnetic propagation were analyzed around a test model in a wind tunnel in DLR (German Aerospace Center). The numerical results indicated that the injected nitrogen gas formed an insulating air film layer on the surface. The thin layer advected backward, maintaining a low temperature without ionization, and covered the object in the wake region. The electromagnetic waves propagated and reached a distant area because the electron density was low. It means that the air film layer acted as a propagation window for the telecommunication waves. Thus, communication blackouts will be avoidable because electromagnetic waves can transmit through the air-film layer. It concluded that the air film effect, developed as a thermal protection technique, is a novel mitigation scheme for reentry blackouts.

To elucidate the role of the Hall effect in magnetohydrodynamic (MHD) aerobraking in rarefied flows,we measured the radial distributions of electron temperature and density in front of a magnetized model in a rarefied argon arcjet wind tunnel using the laser Thomson scattering method. We also developed a water-cooled magnetized model to prevent thermal demagnetization during the measurement. The measured electron density distributions were in excellent agreement with computational fluid dynamics (CFD) predictions. It was also found that the magnetic field had little effect on the electron density distribution around the model. In the case without the magnetic field, the measured electron temperature almost agreed with the CFD prediction. However, the measured electron temperature increase caused by applying the magnetic field was about 1,000 K less than that of the CFD prediction. This discrepancy indicates that the location of an insulating boundary in the plasma is far from the model.

Gas–surface interactions between thermal protection materials and high-enthalpy nonequilibrium flow are one of the greatest challenges in accurately predicting aerodynamic heating during supersonic flights. Finer microscopic details of flow properties are required for elaborate simulation of these interactions. Spectral insight, with quantum-state-specific characteristics, is provided in this work to investigate the physico-chemical processes in high temperature interface of a carbon/carbon (C/C) composite. The nonequilibrium air flow is produced by a 1.2 MW inductively coupled plasma wind tunnel at an enthalpy of 20.08 MJ/kg. The duration of each test is up to 100 s, and quartz is also tested for comparison. Spectral insights into the reaction mechanisms of the gas–surface interactions are acquired by the optical emission spectroscopy and laser absorption spectroscopy. Dynamic evolution of the chemical reaction pathways and thermal nonequilibrium are discussed based on the results of optical emission spectroscopy. Temporally and spatially resolved results of the translational temperature and number density of atomic oxygen are quantified by laser absorption spectroscopy. Controlling mechanisms in the surface chemistry are further analyzed in conjunction with the surface temperature, scanning electron microscopy, and energy dispersive spectroscopy. Reaction mechanisms on the C/C composite surface sequentially experience an oxidation-dominant, an intense competitive, a nitridation-dominant, and a recession dominant period. Distributions in the axial direction and dynamic characteristics of the translational temperature and number density of atomic oxygen are found closely related with surface swelling, recession, and chemical reactions. The results herein are consistent with each other and are instructive to further investigate the interface evolution on C/C composites.

Since the beginning of the Mars planet exploration, the characterization of carbon dioxide hypersonic flows to simulate a spaceship’s Mars atmosphere entry conditions has been an important issue. We have developed a Tunable Diode Laser Absorption Spectrometer with a new room-temperature operating antimony-based distributed feedback laser (DFB) diode laser to characterize the velocity, the temperature and the density of such flows. This instrument has been tested during two measurement campaigns in a free piston tunnel cold hypersonic facility and in a high enthalpy arc jet wind tunnel. These tests also demonstrate the feasibility of mid-infrared fiber optics coupling of the spectrometer to a wind tunnel for integrated or local flow characterization with an optical probe placed in the flow.

This paper studied the flow field properties of the 10 kW inductively coupled plasma wind tunnel (ICPWT). The results can be used for the development of the thermal material protection material for re-entry aerospace vehicles. In this paper, the ICP flow under different input powers was numerically simulated, and the flow-field characteristics in the ICP torch under different operating parameters were obtained. The results showed that when the input power is the typical working power i.e. 10 kW, the electron number density in the plasma torch reaches a maximum of 3.23×1021 1/m3, and the electron temperature is also up to 0.99 eV. Besides, the velocity in the plasma torch reaches a maximum of 34.9 m/s, and the translational temperature also reaches a maximum value of 8740 K.

For the microwave cavity resonance spectroscopy based non-destructive beam monitor for ionizing radiation, an addition-which adapts the approach to conditions where only little ionization takes place due to, e.g., small ionization cross sections, low gas pressures, and low photon fluxes-is presented and demonstrated. In this experiment, a magnetic field with a strength of 57 ± 1 mT was used to extend the lifetime of the afterglow of an extreme ultraviolet-induced plasma by a factor of ∼5. Magnetic trapping is expected to be most successful in preventing the decay of ephemeral free electrons created by low-energy photons. Good agreement has been found between the experimental results and the decay rates calculated based on the ambipolar and classical collision diffusion models.

No abstract available

Plasma resonance probes (PRPs) are used for electron density measurements based on the observation of the plasma resonance (PR) negative peak frequency at the electron plasma frequency in the transmission microwave spectrum. The cylindrical tip-plasma resonance probe (CT-PRP), also known as the cutoff probe, is widely used due to its simple structure. A recent study indicated that increasing the sheath width around the CT-PRP tip resulted in the PR negative peak frequency deviating from the electron plasma frequency and acted as a source of lowering the upper operating pressure limit. This disturbance becomes significant in low-density plasmas ( <1010 cm−3), where thicker sheaths are unavoidable. This study proposes a spherical tip-plasma resonance probe (ST-PRP) to reduce the sheath width effect via the use of a lower sheath impedance of its spherical tip structure. The improved upper operating pressure limit of the ST-PRP was investigated using a three-dimensional electromagnetic simulation model. The results showed that the ST-PRP extended the upper limit of operating pressure and reduced the sensitivity of the upper pressure limit for changes in sheath width greater than the CT-PRP. An experimental study in low electron density capacitively coupled plasma sources was conducted to compare the upper pressure limit between the ST-PRP and the CT-PRP. The results were consistent with the numerical simulation results. We believe that the proposed ST-PRP with an extended upper pressure limit can be a reliable tool for accurate plasma electron density measurements of low-density plasmas using PRPs.

The effect of strong anomalous absorption of the X-mode pump wave associated with two upper-hybrid (UH) plasmon parametric decay is observed in a specially performed model experiment in a laboratory plasma. Strong microwave absorption takes place at a maximal plasma density in the plasma filament higher than the UH resonance value for the frequency equal to the half value of the pump frequency. The anomalous absorption efficiency is determined at the level of 70% in the beginning stage of the parametric decay instability and 40% in the following steady state. A theoretical model of the two UH plasmon decay in strongly inhomogeneous plasma filaments is developed. The localization, threshold, and growth rate of the instability are determined and found to be in agreement with experimental observations.

Microwave plasma thruster (MPT) is one type of electrothermal thruster, inside of which the plasma can be formed through gas heating by microwave energy and accelerated by nozzle to generate thrust. According to the different principle and operating procedure, the specific impulse of MPT is higher than that of chemical thruster and lower than that of magnetic confinement ion and Hull thruster, however the thrust of MPT is higher than that of magnetic confinement ion and Hull thruster and lower than that of chemical thruster. Therefore MPT possesses the excellent qualities of chemical and electric thruster, which will make it has the possibility of applying in space. Inside of the MPT cylindrical cavity, plasma changing procedure and microwave electric field distribution together with TM011 resonant state influence the thruster performance seriously. According to the previous MPT formed through continuous regulation on the resonant sate of cylindrical cavity, it is needed to research a newly fixed and simple MPT, which will simplify the resonant state regulation and provide important basement for further study. Therefore the plasma procedure is analysis to find the best gas discharge condition, otherwise the microwave electric field intensity and power density distribution inside of the cavity running on TM011 resonant sate is calculated to analyse how the parameters is influenced by the cavity dimensions. The resonant state is finely regulated to study how it is influenced by the dimension of cylindrical cavity and microwave coupling probe with ball and half ball structure. The result of theoretical analysis and calculation shows that the lowest discharge power of helium gas is present at the condition of 489Pa and microwave electric density distribution inside of the cavity is beneficial as the ratio of length to diameter greater than 1. As the length and radius of microwave coupling ball probe is suitable, the experiment of resonant state regulation shows that the shortest cylinder cavity is on the best optimum resonant sate, and its resonant frequency is very near to 2.45GHz. The helium discharge experiment demonstrates that this shortest cavity matched by the suitable ball probe have the property of high microwave power utilizing and easy discharge of helium gas, which will make MPT operation reliably.

Methodology for designing the 2.45-GHz microwave (MW) coupling system to optimize the hydrogen plasma density in an electron cyclotron resonance (ECR) plasma reactor is presented. Two different plasma generator systems have been studied by experiments and 3-D simulations to find the criteria to reach an optimized design. The experimental work includes the detailed measurements and calculations of the electron energy distribution functions (EEDF) and ultrafast photography diagnostics to estimate the spatial distributions of plasma unbalanced charge density, potential, and electric field for both cases. It demonstrates that to simulate in 3-D, the distribution of the resonant stationary electric field along the entire MW driver system can be used to improve the design in order to reach higher plasma densities and temperatures.