Spatial Distribution Of Plasma Parameters Research Articles

A planar plume array emanating from an atmospheric pressure argon plasma jet employing floating electrodes

Large-scale plasma plumes downstream of plasma jets are in urgent need from a practical viewpoint. In this Letter, an argon plasma jet with floating electrodes is proposed to produce a large-scale planar plume array. Results indicate that with increasing peak voltage (Vp), the planar plume array elongates gradually and scales up in the lateral direction to an optimal value of 90.0 mm. There is only one discharge pulse per voltage half cycle, whose intensity and duration increase with increasing Vp. Moreover, there is a time lag between the initiations of individual plumes. Fast photography reveals that the planar plume array originates from the repeated process of some micro-discharge filaments stretching along the argon stream. By optical emission spectroscopy, the spatial distribution of plasma parameters is obtained, such as electron density, electron temperature, and gas temperature. At last, the planar plume array is employed to test the surface modification of polyethylene terephthalate, for which a uniform modification has been realized with a scan velocity of 1.0 cm/min. These results are of great significance for the development of large-scale atmospheric pressure plasma sources.

Numerical optimization of dielectric properties to achieve process uniformity in capacitively coupled plasma reactors

This paper presents the results of our numerical analysis to optimize the dielectric properties to achieve process uniformity in the thin film deposition process using capacitively coupled plasma. The difference in the plasma density distribution was analyzed by changing the wafer material from silicon to quartz (or Teflon). Similarly, aluminum was compared with aluminum nitride as the electrode material, and the sidewall material was varied from quartz to a perfect dielectric to study the effect on the plasma characteristics. A two-dimensional self-consistent fluid model was used to analyze the spatial distribution of the plasma parameters. In terms of the process conditions, the gas pressure was set to 400 Pa, the input power was fixed to 100 W, and a radio frequency of 13.56 MHz was used. SiH4/Ar was used as the gas mixture, and these conditions were used as input for numerical simulations of the deposition state of the hydrogenated amorphous silicon layer. The radial spatial distribution of plasma parameters was confirmed to be modified by dielectric elements with low dielectric constants regardless of the type of element. Despite the thin wafer thickness, the use of a wafer with low permittivity weakens the electric field near the electrode edge due to the stronger surface charging effect. Additionally, by changing the material of the sidewall to a perfect dielectric, a more uniform distribution of plasma could be obtained. This is achieved as the peak values of the plasma parameters are located away from the wafer edge. Interestingly, the case in which half of the sidewall was specified as comprising a perfect dielectric and the other half quartz had a more uniform distribution than the case in which the sidewalls consisted entirely of a perfect dielectric.

Optical emission spectroscopy of fiber laser sustained Xe plasma

Laser-sustained plasma (LSP), a unique method of obtaining high brightness broadband light sources, has been used for rapid optical inspection of wafer defects and has thus attracted great interest. Then Xe plasma sustained under high pressure by a continuous fiber laser was investigated using optical emission spectroscopy (OES). Emission spectra of spatial integration diagnosis have shown that with the increase of laser power and the decrease of Gaussian beam focusing number F, the electron temperature fitted by Boltzmann plot method increased from 0.45 eV to 0.85 eV, the corresponding electron density was roughly an order of magnitude of 1016-1017 cm-3, and the calculated absorption coefficient of plasma was distributed in 0.9–1.5 cm-1. To further analyze the spatial distribution of plasma parameters, the spatial resolved OES of LSP was acquired, and the two-dimensional electron temperature and electron density were determined. The non-uniform distribution of the plasma parameters was analyzed due to the existence of thermal gravity convection and forced convection. The serious self-reversal of emission lines of 881.94 nm and 823.16 nm was observed and analyzed.

Simulation of argon-excited microwave plasma reactor for green energy and CO2 conversion application

Microwave plasma as a potential tool to convert CO2 has been extensively studied in recent years. A simulated study on the plasma parameters via the variation of the operating pressure of a microwave plasma model has been performed in this study. The establishment of the model was based on the finite element method to analyse the spatial distribution of plasma parameters in the plasma torch over a period of time. Plasma parameters such as electron potential, density, and temperature were investigated at three different pressures, and the growth of electron potential and density were associated with time. The distribution of molecular ions was observed to be located more on the enter port of the microwave or waveguide near the location of the magnetron at the initial stage. The electron density was found to be constant after it reached maximum value for all the determined pressures. However, the electron temperature behaved differently as compared to the electron potential and density, the distribution of high electron temperature did not enhance during the processing time. The analysis of microwave plasma parameters is beneficial for plasma reactor designing, particularly for CO2 conversion.

Characteristics of very high-frequency plasma with an underexpanded supersonic gas jet

Very high-frequency (VHF) plasma generated with a supersonic gas jet, which is attractive for high-speed and low-damage film deposition in plasma enhanced chemical vapour deposition (PECVD), were investigated experimentally and theoretically. When the gas flow rate was changed under a background pressure in the Torr regime, a unique beam-shaped plasma was clearly observed in the region where an underexpanded jet was generated. It was found through plasma measurement that the plasma parameters are strongly influenced by the spatial structure of the underexpanded gas jet. In particular, the ionization rate was greatly changed according to the local change of gas pressure due to the jet, and the temperature and density of electrons changed by double and one order of magnitude, respectively. These phenomena are considered to be useful to locally control the spatial distribution of plasma parameters.

Effect of the Spatial Distribution of Plasma Parameters on the Operation of a Fusion Reactor

Effect of the Spatial Distribution of Plasma Parameters on the Operation of a Fusion Reactor

Plasma Parameters around a Chain-Like Structure of Dust Particles in an External Electric Field

The formation of a 1D chain-like structure of dust particles in a low-temperature argon plasma was studied. A new numerical model for calculation of the self-consistent spatial distribution of plasma parameters around a chain of dust particles was presented. The model described the motion of positively charged ions in the electric potential of several negatively charged dust particles, taking into account the action of an external electric field. The main advantage of the model was that the charges of the dust particles and the interparticle distances were determined self-consistently. As a result of numerical simulations, the dependencies of the spatial distributions of the plasma parameters (the densities of electrons and ions and the self-consistent electric potential) near the dust particles chain on the strength of the external electric field, an external force acted on the last particle, and the mean free path of the ions was determined. The obtained results made it possible to describe the process of the formation of chain-like structures of dust particles in discharge plasma.

Spatial distribution of plasma parameters by a dual thermal-electrostatic probe in RF and DC magnetron sputtering discharges during deposition of aluminum doped zinc oxide thin films

Aluminum doped zinc oxide thin films deposited by magnetron plasma sputtering are essential for various optoelectronic applications. So far, the oxygen negative ions and the atomic oxygen are regarded as responsible for the poor spatial uniformity of thin film resistivity. While various methods are available for thin film characterization, understanding the growth mechanism requires spatial-resolved measurements of plasma parameters. This work uses a dual thermal-electrostatic probe that is able to reveal the spatial distribution of plasma density, electron temperature and plasma potential. The results exhibit a parabolic profile for plasma density and flat profiles for electron temperature and plasma potential, with no correlation with the strong distribution of thin film resistivity that mirrors the erosion track on the target surface.

Diagnostic and modelling investigation on the ion acceleration and plasma throttling effects in a dual-emitter hollow cathode micro-thruster

Hollow cathode discharges are widely used as neutralizers for the electric propulsion systems and recently developed into micro-thrusters for the small satellites. In this work, a dual-emitter hollow cathode thruster is developed, which can be operated in two different modes—the neutralizer mode and the micro-thruster mode. For characterizing this kind of new device, the Langmuir probe, Faraday probe, and retarding potential analyzer are used to determine the electron temperature, electron density, ion flux, and ion energy distribution function. The operating parameters, including the thrust, and specific impulse, are also measured. A two-dimensional self-consistent extended fluid model is employed to calculate the spatial distribution of plasma parameters and the fluid field of electrons in the region around the emitters. By comparing the diagnostic and modelling results, it is found that the change in the electric field and ionization zone is the essential reason for the different performances of the device in the neutralizer and micro-thruster modes. Variation in the electric field leads to an ion acceleration effect in the micro-thruster mode; moving of the ionization zone raises the plasma pressure in the orifice region of the hollow cathode, and thus leads to enhanced plasma throttling and gas expanding effects. By analyzing the above mechanisms, the possible methods for improving this kind of hollow cathode micro-thruster are discussed.

Numerical 3D Modeling: Microwave Plasma Torch at Intermediate Pressure

This study represents a self-consistent three-dimensional (3D) fluid plasma model coupled with Maxwell equations at an intermediate pressure between 1000 and 5000 Pa. The model was established using the finite element method to analyze the effects of time–space characteristics, which is the variation of plasma parameters with time and the 3D spatial distribution of plasma parameters in the plasma torch at various times. The numerical modeling was demonstrated in three different stages, where the growth of electron density is associated with time. From the distribution characteristics of molecular ions, it can be concluded that they are distributed mainly at the port of the quartz tube of the torch, which is larger than the center of the tube. The density ratio of molecular ion to electron is decreased because of the reduction of pressure and distance, which has been calculated from the port to the center of the quartz tube. The analysis of microwave plasma parameters indicated that intermediate pressure is useful for modeling and plasma source designing, especially for carbon dioxide conversion.

Investigation on the material in the plasma phase by high temporally and spectrally resolved emission imaging during pulsed laser ablation in liquid (PLAL) for NPs production and consequent considerations on NPs formation

In this paper experimental temperature and density maps of the laser induced plasma in water during pulsed laser ablation in liquid (PLAL) for the production of metallic nanoparticles (NPs) has been determined. A detection system based on the simultaneous acquisition of two emission images at 515 and 410 nm has been constructed and the obtained images have been processed simultaneously by imaging software. The results of the data analysis show a variation of the temperature between 4000 and 7000 K over the plasma volume. Moreover, by the study of the temperature distribution and of the number densities along the plasma expansion axis it is possible to observe the condensation zone of the plasma where NPs can be formed. Finally, the time associated with the electron processes is estimated and the plasma charging effect on NPs is demonstrated. The set of observations retrieved from these experiments suggests the importance of the plasma phase for the growth of NPs and the necessity of considering the spatial distribution of plasma parameters for the understanding of one of the most important issues of the PLAL process, that is the source of solid material in the plasma phase.

Automatic scanning system to detect plasma radiation

In this study, the spatial distribution of plasma parameters in an experimental RF plasma device was performed. An automatic scanning system for the spectrometer and linear drive to detect plasma radiation was developed and implemented. The system is used to measure the spatial distribution of the electron temperature in a plasma discharge.

Spatial characterization of red and white skin potatoes using nano-second laser induced breakdown in air

We presents spectroscopic study of the plasma generated by a Q-switched Nd:YAG (1064 nm) laser irradiation of the flesh of red and white skin potatoes. From the spectra recorded with spectrometer (LIBS2500+, Ocean Optics, USA) 11 elements were identified in red skin potato, whereas, the white skin potato was found to have nine elements. Their relative concentrations were estimated using CF-LIBS method for the plasma in local thermodynamic equilibrium. The target was placed in ambient air at atmospheric pressure. The electron temperature and number density were calculated from Boltzmann plot and stark broadened line profile methods, respectively using Fe I spectral lines. The spatial distribution of plasma parameters were also studied which show a decreasing trend of 6770 K–4266 K and (3–2.0) × 1016 cm-3. Concentrations of the detected elements were monitored as a function of depth of the potatoes. Our study reveals a decreasing tendency in concentration of iron from top to the centre of potato’s flesh, whereas, the concentrations of other elements vary randomly.

Study on spatial distribution of plasma parameters in a magnetized inductively coupled plasma

Spatial distributions of various plasma parameters such as plasma density, electron temperature, and radical density in an inductively coupled plasma (ICP) and a magnetized inductively coupled plasma (M-ICP) were investigated and compared. Electron temperature in between the rf window and the substrate holder of M-ICP was higher than that of ICP, whereas the one just above the substrate holder of M-ICP was similar to that of ICP when a weak (<8 G) magnetic field was employed. As a result, radical densities in M-ICP were higher than those in ICP and the etch rate of oxide in M-ICP was faster than that in ICP without severe electron charging in 90 nm high aspect ratio contact hole etch.

Spectroscopic characterization of laser ablated silicon plasma

We report plasma parameters of laser ablated silicon plasma using the fundamental (1064 nm) and second harmonics (532 nm) of a Nd : YAG laser. The electron temperature and electron number density are evaluated using the Boltzmann plot method and Stark broadened line profile, respectively. The electron temperature and electron number density are deduced using the same laser irradiance 2–16 GW cm−2 for 1064 nm and 532 nm as 6350–7000 K and (3.42–4.44) × 1016 cm−3 and 6000–6400 K and (4.20–5.72) × 1016 cm−3, respectively. The spatial distribution of plasma parameters shows a decreasing trend of 8200–6300 K and (4.00–3.60) × 1016 cm−3 for 1064 nm and 6400–5500 K and (5.10–4.50) × 1016 cm−3 for 532 nm laser ablation. Furthermore, plasma parameters are also investigated at low pressure from 45 to 550 mbar, yielding the electron temperature as 4580–5535 K and electron number density as (1.51–2.12) × 1016 cm−3. The trend of the above-mentioned results is in good agreement with previous investigations. However, wavelength-dependent studies and the spatial evolution of plasma parameters have been reported for the first time.

Discharge Characterization of the Coaxial Magnetoisolated Longitudinal Anode Hall Thruster

The coaxial magnetoisolated longitudinal anode concept was introduced to improve efficiency and lifetime of low-power Hall thrusters (). The coaxial magnetoisolated longitudinal anode represents a significant departure from conventional Hall thrusters and has not been thoroughly studied yet. The high efficiency of the thruster, as validated by measurements, increases the need for a better understanding of the physical processes in this type of thruster. An analysis of the coaxial magnetoisolated longitudinal anode discharge based on experimental measurements was conducted for this aim. The experimental setup includes electrical probes mounted on a fast moving positioner, enabling one to obtain the spatial distribution of plasma parameters inside the thruster channel. The results confirmed the basic assumptions used in the physical model of the coaxial magnetoisolated longitudinal anode concept and revealed new phenomena related to the radial nonuniformity of the discharge. In particular, focusing equipotentials were discovered not only in the anode cavity but also in the dielectric channel, where the area of intense ionization was located. The physical processes contributing to the formation of the focusing equipotentials are discussed.

Two-dimensional-spatial distribution measurement of electron temperature and plasma density in low temperature plasmas

A real-time measurement method for two-dimensional (2D) spatial distribution of the electron temperature and plasma density was developed. The method is based on the floating harmonic method and the real time measurement is achieved with little plasma perturbation. 2D arrays of the sensors on a 300 mm diameter wafer-shaped printed circuit board with a high speed multiplexer circuit were used. Experiments were performed in an inductive discharge under various external conditions, such as powers, gas pressures, and different gas mixing ratios. The results are consistent with theoretical prediction. Our method can measure the 2D spatial distribution of plasma parameters on a wafer-level in real-time. This method can be applied to plasma diagnostics to improve the plasma uniformity of plasma reactors for plasma processing.

Semiempirical model for analysis of inhomogeneous optically thick laser-induced plasmas

In this paper, a more realistic approach of a non-uniform optically thick plasma in local thermodynamic equilibrium was applied to describe self-reversal of Co I 340.51 nm emission line recorded from a laser-induced plasma generated on a Co–Cr–Mo metallic alloy. This line was selected because it is one of the most absorbed of the major elements in air at atmospheric pressure. The model describes the behavior of the plasma after the breakdown, and it was semiempirical thus, some information was taken from the experiment. A cylinder-symmetrical plasma column with a parabolic temperature distribution having a maximum at the center and decreasing toward the edges was considered. The input parameters were the plasma length, the temperature in the plasma core, and the Co total density, which were estimated from measurements and previous work. Moreover, the distribution of electron density depended on the temperature, and the ionization degree was taken into account through Saha equation. Then, plasma parameters were adjusted in such a way calculations reproduced the experimentally measured line profiles. The effect of varying laser power on plasma homogeneity and its evolution in time were investigated. Moreover, preliminary results of spatial distribution of plasma parameters were obtained that confirmed the practical application of the model on plasma diagnostics.

Three-dimensional modelling of the laser-induced plasma plume characteristics in laser welding

Modelling results are presented concerning the spatial distribution of plasma parameters in a laser-induced plasma plume with laser welding as the research background. In the modelling, the plasma plume characteristics are affected by many factors, such as the temperature and flow velocity of the metal vapour leaving the welded workpiece surface, the velocity of the shielding gas injected coaxially with the laser beam, the velocity of the assisting gas injected laterally with respect to the workpiece, and the energy absorption and radiation heat loss of the plasma plume. Typical computed distributions of temperature, velocity, vapour concentration, absorption coefficient and the refraction index within the plasma plume are presented with the continuous-wave (CW) CO2 laser welding of an iron workpiece as the calculation example. The predicted temperatures of the plasma plume are shown to be reasonably consistent with the corresponding experimental data. It is also shown that the metal-vapour/shielding-gas momentum ratio plays an important role in determining the height of the plasma plume formed in the laser welding. Due to the cooling effect of the shielding gas, the dimensions of the plasma plume will become smaller and thus laser absorption and refraction by the plasma plume can be reduced by increasing the shielding-gas velocity. The laterally injected assisting gas may also significantly affect the plasma plume and thus can be used to control the effect of the laser-induced plasma plume on the laser welding process.

Effects of filament positions on the arc discharge characteristics of a negative hydrogen ion source for neutral beam injector

The influence of filament positions on the arc discharge characteristics of a negative hydrogen ion source for a neutral beam injector were studied by simulations and experiments. We have made a simulation code named “PRIMELOC2,” which calculates the orbits of primary electrons emitted from cathode filaments, including collisions with H2 gas molecules filled in the source, to obtain the spatial distribution of ionization points. We applied this code to a large negative hydrogen ion source having an external magnetic filter for LHD-NBI No. 1 (neutral beam injector 1 for a large helical device). As a result of the calculations, we have found that the moving area of emitted primary electrons differs markedly according to the filament positions. Calculation results agreed well with the experimental results of high-power arc discharge and the spatial distribution of plasma parameters obtained by Langmuir probe measurements. By applying PRIMELOC2 to filament–arc ion sources, we can choose appropriate areas in arc chambers for filament positioning.