Distribution Of Plasma Parameters Research Articles

Simulation and experimental research on the parameter distribution of low-pressure Ar/O2 inductivly coupled plasma

Adding electronegative gas to the inert gas is an important means of adjusting the plasma parameter distribution. In this paper, a fluid model of the Ar/O2 inductivly coupled plasma (ICP) is used to investigate the parameter distribution, while the electron energy distribution function (EEDF) and the transport coefficients are obtained by the Boltzmann equation solver module to improve the accuracy. The spatial-temporal evolution of the electron density and the electron temperature of the ICP are obtained and the influence of the discharge power and the oxygen mole ratio on the distribution of the ICP parameters is compared. Additionally, the physical mechanism is researched using the diffusion-transport theory of the plasma. In order to verify the reliability of the model results, an experiment is carried out to diagnose the discharge parameters. The results of the simulation and the experiment are performed for different power and oxygen mole ratios and a good qualitative and numerical agreement is obtained, indicating that the inclusion of the simulation results in a high accuracy.

Contemporaneous EMIC and whistler mode waves: Observations and consequences for MeV electron loss

AbstractThe high variability of relativistic (MeV) electron fluxes in the Earth's radiation belts is partly controlled by loss processes involving resonant interactions with electromagnetic ion cyclotron (EMIC) and whistler mode waves. But as previous statistical models were generated independently for each wave mode, whether simultaneous electron scattering by the two wave types has global importance remains an open question. Using >3 years of simultaneous Van Allen Probes and THEMIS measurements, we explore the contemporaneous presence of EMIC and whistler mode waves in the same L shell, albeit at different local times, determining the distribution of wave and plasma parameters as a function of L, Kp, and AE. We derive electron lifetimes from observations and provide the first statistics of combined effects of EMIC and whistler mode wave scattering on MeV electrons as a function of L and geomagnetic activity. We show that MeV electron lifetimes are often strongly reduced by such combined scattering.

Identification of seismic activity sources on the subsatellite track by ionospheric plasma disturbances detected with the Sich-2 onboard probes

Using a cylindrical Langmuir probe and the authors’ proprietary two-channel pressure transducer, ionospheric plasma parameter distributions along the orbit of the Sich-2 satellite (Ukraine, 2011–2012) were measured. This paper is concerned with identifying the space–time location of ionospheric plasma disturbance sources, including the epicenters of actual earthquakes (before or during the satellite flyover) and incipient earthquakes on the subsatellite track, from the measured distributions of the electron density and temperature and the neutral particle temperature along the satellite orbit. To do this, the measured ionospheric plasma parameter distributions are connected to the coordinates on the subsatellite track.It is shown that local disturbances in the electron density and temperature and neutral particle temperature distributions in the satellite orbit in the ionosphere may serve as indicators of seismic activity on the subsatellite track. The epicenters of incipient earthquakes may be set off from other plasma parameter disturbance sources associated with seismic activity using information provided by special monitoring and survey centers that monitor the current seismic situation.

Axial distribution of plasma fluctuations, plasma parameters, deposition rate and grain size during copper deposition

ABSTRACTFloating potential fluctuations, plasma parameters and deposition rate have been investigated as a function of axial distance during deposition of copper in direct current (DC) magnetron sputtering system. Fluctuations were analyzed using phase space, power spectra and amplitude bifurcation plots. It has been observed that the fluctuations are modified from chaotic to ordered state with increase in the axial distance from cathode. Plasma parameters such as electron density (ne), electron temperature (Te) and deposition rate (Dr) were measured and correlated with plasma fluctuations. It was found that more the deposition rate, greater the grain size, higher the electron density, higher the electron temperature and more chaotic the oscillations near the cathode. This observation could be helpful to the thin film technology industry to optimize the required film.

The three-dimensional positioning system at the VINETA.II experiment—a multipurpose tool for in situ plasma diagnostics

The manipulator systems installed at the VINETA.II magnetic reconnection experiment are essential elements for experimental investigation of local plasma parameters. A novel three-dimensional (3D) probe manipulator has been designed, implemented and successfully operated at VINETA.II. This work presents its design and performance for three-dimensional measurements of VINETA.II plasmas. Its design consists of three vertically stacked independent and mutually perpendicular linear motion stages which allow flexible positioning of diagnostic tools such as electrical and magnetic probes or optical diagnostics within the vacuum vessel. Its design features include a wide spatial coverage, sub-millimeter positioning accuracy and the capability to operate in a harsh environment under the influence of microwaves, radio-frequency waves and direct contact with plasma. Manipulator performance is assessed by measuring a volumetric distribution of plasma parameters by a B-dot probe. A typical discharge of the magnetic reconnection setup in VINETA.II with a pulse time of τ=600 μs is chosen for this purpose. The azimuthal magnetic field distribution measured with the 3D manipulator agrees favorably with measurements obtained by the two-dimensional (2D) manipulator, used at VINETA.II as a standard reference diagnostic tool, thereby demonstrating its reliability and performance. A programmable stepper motor controller (TMCM-1110) that is operated remotely by a PC drives all possible features of the manipulator system.

Spatial distributions of plasma parameters in inductively coupled hydrogen discharges with an expansion region

Spatial distributions of plasma parameters have been investigated by a Langmuir probe in a hydrogen inductively coupled plasma with an expansion region. The influence of the gas pressure and the radio-frequency power on the electron energy probability function (EEPF), electron density, and electron temperature has been presented. The results indicate that the EEPF evolves from a bi-Maxwellian distribution in the discharge driver region to a Maxwellian distribution in the expansion region at low pressures, whereas it is always characterized by a Maxwellian distribution at high pressures. Moreover, the electron density exhibits a bell-shaped profile in the driver region, while the electron temperature shows a relatively uniform distribution there, and they decrease to low values in the expansion region. In order to verify the experimental results, we use the COMSOL simulation software to calculate the electron density and electron temperature at different powers at 2 Pa. The simulated and measured axial distributions of the plasma properties agree well except for the absolute value, i.e., the calculated electron temperature is higher at all the RF powers, and the calculated electron density is underestimated at 2 kW, while a better agreement is obtained at low RF power.

Specific features of the radial distributions of plasma parameters in the initial segment of a supersonic jet generated by a pulsed capillary discharge

Results are presented from spectroscopic studies of the initial segment of a supersonic plasma jet generated by a pulsed capillary discharge with an ablative carbon-containing polymer wall. Specific features of the spatial distributions of the electron density and intensities of spectral components caused, in particular, by the high electron temperature in the central zone, much exceeding the normal temperature, as well as by the high nonisobaricity of the initial segment of the supersonic jet, are revealed. Measurements of the radiative properties of the hot jet core (the intensity and profile of the Hα and Hβ Balmer lines and the relative intensities of C II lines) with high temporal (1–50 μs) and spatial (30–50 μm) resolutions made it possible to determine general features of the pressure and temperature distributions near the central shock. The presence of molecular components exhibiting their emission properties at the periphery of the plasma jet allowed the authors to estimate the parameters of the plasma in the jet region where “detached” shock waves form.

Experimental Investigation of Non-Isolated Dust Particles on the Plasma Characteristics in Direct Current System

This paper reviews the radial profile of plasma parameters in the present and absent of nonisolated dust particles at different positions from the cathode surface. The results of voltage and current discharge shown that the present of dust did not effect of the behavior of discharge voltage but it decreased the discharge current. However, the measurement of radial distribution of plasma parameters along the cathode at different distance (2 cm and 4 cm) from it shown that, all plasma parameters are non-homogenous distribution along the cathode in the cathode sheath and plasma bulk. Moreover, according to radial profile of plasma potential, the charge of copper dust particles is negative in the plasma sheath but it is charged postively in the plasma bulk.

Influence of the inter-electrode gap on the cathode sheath characteristics (voltage drop across it and its thickness)

This paper is devoted to studying how the inter-electrode distance affects the voltage drop across electrodes, the cathode sheath thickness, and the axial distribution of plasma parameters. The experiment demonstrates the simultaneous growth of both the voltage drop across the electrodes and the cathode sheath thickness when on increasing the gap the anode is moved away from the cathode while remaining in the negative glow. This effect is most clearly pronounced under low gas pressure and high current values when the negative glow length is large. The discharge axial structure dynamics is studied with the Langmuir probe technique and with the OOPIC Pro code. The inter-electrode gap growth with the current fixed is found to be accompanied by the plasma concentration increase in the negative glow. The positive plasma potential is shown to cause the current to the grounded anode to be transported by fast electrons accelerated in the cathode sheath. Moving the anode away from the cathode through the negative glow weakens the flow of fast electrons coming to the anode, thus decreasing the discharge current. In order to restore the discharge current, one has to increase the voltage across the electrodes, leading to the cathode sheath thickness increase and the plasma concentration growth in the negative glow.

Effect of electron temperature on the distribution of plasma parameters on the phase planes for thermionic diode with low temperature emitter

Influence of temperature distribution of thermal and fast electrons on the distribution of the ion current density in the electrode gap diode has been studied. Studies on the phase planes, especially in the plane of the plasma density – ion current density have been carried out. It is shown that the generation of ions in the electrode gap is specified by the fast electron temperature.

The distribution of oscillation frequency of magnetic field and plasma parameters in BBFs: THEMIS statistics

AbstractBursty bulk flows (BBFs) have been correlated with Pi2 pulsations and damping oscillations of plasma velocity in many investigations. But the oscillation time scales in BBFs are still an open question. The purpose of this study is to statistically study the oscillated frequency distribution of magnetic field and plasma parameters inside BBFs. The data are obtained by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes during the period of 2008 to 2011. For 424 selected BBF events, we use the wavelet spectrum analysis to select the main, second, and third period components of the magnetic field and plasma parameters according to their largest, second, and third largest values of the wavelet power spectral density, respectively. The power spectra show repeated information in the form of multiple peaks or oscillations. The quasi‐Gaussian distribution is a good model for the occurrences of the main and secondary periods. The most probable main periods of the magnetic field and plasma parameters are between 143 s and 160 s, which are located in the frequency band of Pi2 and Pi3 pulsations. The second and third period ranges from 63 s to 70 s and from 34 s to 37 s, respectively. Main periods of these parameters change little with the radial distance. We conclude that periods of these parameters are formed at the beginning of BBF history. Although the distribution model cannot give the dynamic processes, it identifies the intrinsic frequencies in oscillations of magnetic field and ion velocity inside of BBFs.

Modelling of local ion nitriding in a glow discharge with hollow cathode

The paper presents the results of computer calculations of glow discharge plasma parameters in a hollow cathode zone and modeling of thermal and diffusion processes at local ion nitriding with a hollow cathode. The proposed model of a glow discharge with a hollow cathode with sufficient accuracy allowed to describe the distribution of plasma parameters in a cathode void. Values of plasma parameters in a cathode void formed by a mesh screen and cathode surface were obtained via the probe method. It was found that the use of hollow cathode effect allows to increase the concentration of ions near the treated surface by 1.5 times. The suggested computer model allows to predict the distribution of the temperature field and depth of a diffusion layer at local ion nitriding with a hollow cathode for various configurations and sizes.

Low-voltage beam discharge in light inert gases to solve problems of voltage stabilization

By means of the flat one-sided probe, the electron velocity distribution function is investigated along with plasma parameters distribution and electrokinetic characteristics in short (without positive column) low-voltage beam discharge in helium, neon, and argon. With the pressure increase, the discharge voltage obtains the value of the excitation potential of the metastable level of the filling gas, U m. The results of the probe measurements of the electron velocity distribution function make it possible to calculate the generation functions of the inelastic process and to make the conclusion that, at attaining the critical pressure, P cr, when the processes of atom stepwise ionization begin to dominate over the direct ionization, the discharge burning voltage drops below the ionization potential, U ion. Based on the performed studies, a technique and a device are proposed to stabilize the voltage within the range of 9–50 V by filling the interelectrode gap with inert gases of different excitation and ionization potentials.

Macroscopic motion of sheath-connected blobs in magnetic fields with arbitrary topology

In this study, macroscopic motion of sheath-connected blobs in magnetic fields, having arbitrary topology of the field lines and unfrozen in plasma, is analyzed within the electrostatic limit. Two distinct cases of magnetic configurations, with small and large curvature of the field lines, are considered and the criterion to discern them is deduced. For magnetic configurations with small curvature of the field lines, it is demonstrated that asymmetry of plasma distribution at the blob ends can drive macroscopic motion of a filament due to formation of unequal sheath potentials and establishing the effective Boltzmann potential. For a specific case of magnetic fields with small curvature of the field lines and identical metrics at the sheaths, we show that macroscopic motion of a plasma filament is determined by an effective electrostatic potential, which remains constant in time. For magnetic configurations with large curvature of the field lines, it is shown that motion of sufficiently large blobs is governed by integral distribution of plasma and magnetic field parameters along the field lines leading to blob adjusting its shape and position to the lead of the magnetic field lines in the course of its motion, whereas propagation of small and medium sized blobs can be represented as mutually independent motion of filament transverse cross-sections across the magnetic field lines. The qualitative conclusions on regularities of filament motion are supplied with numerical simulations of blob dynamics in two cases of tokamak-like magnetic fields with sheared and non-sheared field lines.

On the magnetohydrodynamics flows in curved coaxial channels

Stationary plasma flows obtained by using numerical solutions of corresponding stationary problems in curved coaxial channels are considered. It is supposed that plasma interacts with own azimuthal magnetic field. The main attention of the paper is focused on accelerating transonic flows, which attract a considerable interest in the theory of plasma accelerators. It was demonstrated that a curvilinear configuration of a channel makes the significant contribution to distributions of basic plasma parameters.

The magnetic field application for the gas discharge plasma control in processes of surface coating and modification

In this paper the method of magnetic field application to control the gas discharge plasma effect on the various surfaces in processes of surface coating and modification is considered. The magnetic field directed perpendicular to the direction of electric current in the gas discharge plasma channel is capable to reject this plasma channel due to action of Lorentz force on the moving electrically charged particles [1,2]. The three-dimensional spatial structure of magnetic field is created by system of necessary quantity of the magnets located perpendicular to the direction of course of electric current in the gas-discharge plasma channel. The formation of necessary spatial distribution of magnetic field makes possible to obtain a required distribution of plasma parameters near the processed surfaces. This way of the plasma channel parameters spatial distribution management is the most suitable for application in processes of plasma impact on a surface of irregular shape and in cases when the selective impact of plasma on a part of a surface of a product is required. It is necessary to apply automated computer management of the process parameters [3] to the most effective plasma impact.

Current sheets in the Earth’s magnetosphere and in laboratory experiments: The magnetic field structure and the Hall effect

The main characteristics of current sheets (CSs) formed in laboratory experiments are compared with the results of satellite observations of CSs in the Earth’s magnetotail. We show that many significant features of the magnetic field structure and the distributions of plasma parameters in laboratory and magnetospheric CSs exhibit a qualitative similarity, despite the enormous differences of scales, absolute values of plasma parameters, magnetic fields, and currents. In addition to a qualitative comparison, we give a number of dimensionless parameters that demonstrate the possibility of laboratory modeling of the processes occurring in the magnetosphere.

Typical Profiles and Distributions of Plasma and Magnetic Field Parameters in Magnetic Clouds at 1 AU

Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs). They are important because of their simple internal magnetic field configuration, which resembles a magnetic flux rope, and because they represent one of the most geoeffective types of solar transients. In this study, we analyze their internal structure using a superposed epoch method on 63 events observed at L1 by the Advance Composition Explorer (ACE), between 1998 and 2006. In this way, we obtain an average profile for each plasma and magnetic field parameter at each point of the cloud. Furthermore, we take a fixed time-window upstream and downstream from the MC to also sample the regions preceding the cloud and the wake trailing it. We then perform a detailed analysis of the internal characteristics of the clouds and their surrounding solar wind environments. We find that the parameters studied are compatible with log-normal distribution functions. The plasma $\beta $ and the level of fluctuations in the magnetic field vector are the best parameters to define the boundaries of MCs. We find that one third of the events shows a peak in plasma density close to the trailing edge of the flux ropes. We provide several possible explanations for this result and investigate if the density peak is of a solar origin (e.g. erupting prominence material) or formed during the magnetic cloud travel from the Sun to 1 AU. The most plausible explanation is the compression due to a fast overtaking flow, coming from a coronal hole located to the east of the solar source region of the magnetic cloud.

Dynamics of self-compressed argon and helium plasma streams in the MPC facility

The results of experimental investigations on self-compressed plasma streams and compression zone formation are presented for varied mass flow rate and initial concentrations of particles of working gas that depend on initial pressure. Experiments were carried out in the Magnetoplasma Compressor (MPC) facility. Space–time distributions of the electric current and electron density in the plasma stream compression region were measured under different experimental conditions. High-speed images of plasma stream dynamics in the MPC accelerating channel with a high temporal resolution were also obtained for different initial pressures. The experimental results show a strong dependence of plasma stream parameters and compression zone location on the initial gas concentration. The maximum electron density is obtained in the range of Ne = (1 ÷ 5) × 1018 cm−3. Plasma streams have a good radial symmetry under all experimental conditions. The distributions of plasma parameters along the plasma stream flows are discussed.

A FOUR-FLUID MHD MODEL OF THE SOLAR WIND/INTERSTELLAR MEDIUM INTERACTION WITH TURBULENCE TRANSPORT AND PICKUP PROTONS AS SEPARATE FLUID

ABSTRACT We have developed a four-fluid, three-dimensional magnetohydrodynamic model of the solar wind interaction with the local interstellar medium. The unique features of the model are: (a) a three-fluid description for the charged components of the solar wind and interstellar plasmas (thermal protons, electrons, and pickup protons), (b) the built-in turbulence transport equations based on Reynolds decomposition and coupled with the mean-flow Reynolds-averaged equations, and (c) a solar corona/solar wind model that supplies inner boundary conditions at 40 au by computing solar wind and magnetic field parameters outward from the coronal base. The three charged species are described by separate energy equations and are assumed to move with the same velocity. The fourth fluid in the model is the interstellar hydrogen which is treated by separate continuity, momentum, and energy equations and is coupled with the charged components through photoionization and charge exchange. We evaluate the effects of turbulence transport and pickup protons on the global heliospheric structure and compute the distribution of plasma, magnetic field, and turbulence parameters throughout the heliosphere for representative solar minimum and maximum conditions. We compare our results with Voyager 1 observations in the outer heliosheath and show that the relative amplitude of magnetic fluctuations just outside the heliopause is in close agreement with the value inferred from Voyager 1 measurements by Burlaga et al. The simulated profiles of magnetic field parameters in the outer heliosheath are in qualitative agreement with the Voyager 1 observations and with the analytical model of magnetic field draping around the heliopause of Isenberg et al.