Spatial Distribution Of Electron Temperature Research Articles

An incoherent Thomson scattering system for measurements near plasma boundaries.

Laser Thomson scattering (LTS) is a minimally invasive measurement technique used for determining electron properties in plasma systems. Sheath model closure validation requires minimally invasive measurements of the electron properties that traverse the boundaries between the bulk plasma, the presheath, and the plasma sheath. Several studies have probed the radial properties along the surface of discharge electrodes with laser-based diagnostics and electrostatic probes. These measurements provide valuable insight into the electron properties in this dynamic region. However, sheath model calibration requires plasma property measurements perpendicular to plasma bounding surfaces, in this case, along the electrode normal vector between discharge electrodes. This work presents the development of a discharge plasma cell and laser Thomson scattering system with a measurement volume step of 1mm normal to plasma bounding surfaces. The laser Thomson scattering measurements are made between a set of discharge electrodes separated by ∼25mm that are used to generate a pulsed argon plasma. The spatial distribution of electron temperature and density is measured at several discharge voltages between 8 and 20kV at a pressure of 8 Torr-Ar. It is determined that the system is statistically stationary and resembles a classic DC discharge plasma. The results are some of the first laser diagnostic-based "between electrode" measurements made along the plasma bounding electrode normal vector. A one-dimensional sheath model is applied to determine the near cathode electron properties, and it is determined that the edge of the presheath is probed in the high-voltage cases. As the lengths of the presheath and sheath decrease with decreasing voltage, the region recedes below the closest probed point to the cathode. To improve the performance of the diagnostic, the step size of the interrogation volume should decrease by an order of magnitude from 1mm to less than 100 μm, and the data acquisition strategy should be revised to increase the signal-to-noise ratio.

Rare earth effect on laser produced plasma dynamics during pulsed laser deposition of doped cobalt ferrite

The addition of rare earth elements the ferrites can lead to significant changes in structural, magnetic and electric properties of bulk materials and also of thin films deposited by pulsed laser deposition. The present study relies on the analysis of the laser induced plasma of three sets of cobalt ferrite targets doped with various concentrations of RE elements (Dy, Gd, Yb) and proposes a correlation of the derived results with structural investigations of the films obtained during the same experiment. ICCD imaging and space-and time-resolved optical emission spectroscopy techniques were used to obtain information on the dynamics and excitation temperatures of various species found in the laser produced plasmas (LPP). Initial investigations on the global behavior of the LPP revealed that the addition of RE reduced the drift velocities of the formed plasma structures, the lowest ones being observed for the targets doped with the heaviest RE (Yb). Space-and time-resolved spectroscopy measurements applied for all main elements (Fe, Co and RE - both neutral and ionic species) showed a complex dynamic system, with decreased/increased kinetic energies for neutrals/ions at high dopant concentrations, suggesting a possible re-sputtering effect at the films surface. The individual excitation temperatures of the main elements derived from Boltzmann plots increased as the RE content was augmented via radiative collision events due to their larger diameters compared with Co, Fe or O. The spatial distribution of electron temperature can be explained by the charge separation occurring with the addition of RE in the investigated systems.

2-D Finite-Element Modeling of Surface Dielectric Barrier Plasma Discharge Devices to Understand the Influence of Design Parameters on Sterilization Applications

In this study, voltage distribution and surface dielectric barrier discharge (DBD) of a microplasma discharge device (MDD) were modeled in 2-D domain using finite-element analysis (FEA). Initially, the voltage distribution across comb-, H-tree-, and honeycomb-structured MDD was analyzed. Then, the cross section of an MDD consisting of a polyimide-based dielectric sandwiched between two copper electrodes was used for modeling the microplasma discharge characteristics in an argon environment. A sinusoidal voltage was applied to one of the copper electrodes while the other electrode was grounded. The spatial distributions of electron temperature (ET) across the electrodes for varying input voltages were simulated to demonstrate the importance of breakdown voltage. A detailed analysis on the effect of varying electrode and dielectric barrier thicknesses on electron density and ET was also performed to understand the importance of optimizing device configurations for microplasma discharge. Moreover, MDD was also simulated in varying ambient temperature and pressure conditions to evaluate their effect on ET and density across the electrodes. The results from these simulations provide a better understanding of parameters such as varying input voltage, electrode, and dielectric thickness on ET and electron density. This enables us to optimize design parameters for fabricating MDDs and the operating conditions for effective sterilization applications.

One-dimensional simulation of Ar dielectric barrier discharge driven by combined rf/dc sources at atmospheric pressure

<sec>We present the dielectric barrier discharge (DBD) mechanism of argon (Ar) plasma driven by a combination of radio frequency (rf) voltage source and direct current (dc) voltage source at atmospheric pressure, based on one-dimensional self-consistent coupled fluid model. Using the finite element method (FEM) to numerically calculate the model, the average value of period average electron density varying with the average value of period average gas voltage in one rf period, and the variation of the minimum rf sustaining voltage are obtained under different dc voltages. In addition, the spatiotemporal distribution of the electron density and electron generation rate, the spatial distribution of electron temperature, and the time-domain variation of electron conduction current flowing to the dielectric are studied. The results show that the introduction of the dc voltage source has a significant effect on the rf discharge process of atmospheric pressure Ar gas, and the parameters of the plasma state are changed correspondingly. The discharge process is mainly controlled by the air gap voltage, and the dc voltage affects the gap voltage by changing the charge density on the dielectric surface. The minimum rf sustaining voltage <i>V</i><sub>rf,min </sub>first increases and then decreases with the increase of dc voltage. The amplitude of rf minimum sustaining discharge voltage is changed by the dc voltage. And when the amplitude is reached or exceeded, the discharge is controlled by the rf power supply.</sec><sec>On the one hand, in the <i>α</i> mode, when the dc voltage is low, electrons are generated near the ground electrode. The electric field intensity in the ionization area is too small to maintain ionization. When the dc voltage is high, the sheath is formed, and electrons are generated near the rf sheaths on both sides and the boundary of the plasma region. In the γ mode, when the rf voltage amplitude is equal to or greater than the rf minimum sustain discharge voltage amplitude, i.e. <i>V</i><sub>rf </sub>≥ <i>V</i><sub>rf,min</sub>, the generation and distribution of electrons are almost unaffected by the dc voltage.</sec><sec>On the other hand, in the <i>α</i> mode, the ionization cannot be sustained for the low dc voltage, resulting in the failure to form the main plasma area. Therefore, the electron temperature is generally high. Owing to the high electron density near the ground electrode, the electron temperature is higher. The electron density near the dielectric is less than that near the electrode, so the temperature is lower. When the dc voltage is getting larger, the sheath and the main plasma region are formed. The dc voltage significantly affects the electron temperature by controlling the sheath voltage and the length of the main plasma region.</sec><sec>Finally, in the α mode, the electron density near the medium is very low and the air gap voltage is negative for the low dc voltage. As a result, few electrons can reach the surface of the dielectric, and the conduction current of electrons flowing to the medium is very small. With the increase of the dc voltage, the electric field across air gap increases, and electrons, under the action of the electric field, flow from the dielectric surface. The sheath having formed, some speedy non-localization electrons that have reached the dielectric surface are reflected back to the sheath, resulting in a significant reduction in the number of electrons that can reach the dielectric surface.</sec>

Determination of electron properties of a helium atmospheric pressure plasma jet with a grounded metallic target

AbstractAn atmospheric pressure plasma jet (APPJ) was configured to generate helium atmospheric pressure plasma. A kilohertz AC voltage was applied to APPJ electrodes, and a grounded aluminum target was placed outside of a quartz tube on the plasma propagation axis. The electron temperature and density of APPJ were determined using the emissivity of continuum radiation in 380–500 nm spectra. Electron temperatures and densities for the helium plasmas with and without a target were compared. When the target was installed, the continuum radiation was enhanced, and electron density increased. Spatial distributions of electron temperature and density from the nozzle of the quartz tube to the target were examined. The electron temperature increased up to ∼2.75 eV, and electron density increased and decreased along APPJ propagation.

Numerical study on the influence of electron temperature on void formation in dusty plasma

In the past, experiments have proven that the electron temperature in the void is lower than that in the dust cloud. Based on this point, the influence of the spatial distribution of the electron temperature on the void is studied by calculating the fluid equation with explicit ionization, and the images of the circular void and the ring void are obtained by simulation. It is found that when the electron temperature is greater than the threshold value, a stable circular void is generated, and as the electron temperature increases, the time required for the circular void to reach a steady state decreases and its size decreases. This law is not affected by electron temperature spatial distribution set in the center. Combined with the studies of circular void, we speculate that the electron temperature in the ring void is also lower than that in the dust cloud. Through the assumption of the spatial distribution of electron temperature, the simulation results in a ring-shaped void. And the influence of the intensity of the spatial variation of the electron temperature on the ring void is verified. The results show that when the electron temperature change is severe enough, a ring void is generated. And as the intensity increases, the time required for the ring void to reach a steady state decreases, and the size increases slightly.

Langmuir probe diagnostics of an impulse magnetron discharge with hot Cr target

Impulse magnetron discharge (pulse duration 20 ms) with uncooled Cr target has been investigated with a specially designed Langmuir probe setup in a wide range of parameters (magnetic field and discharge power). The spatial distributions of electron temperature and plasma density have been measured in the gasless self-sputtering mode. It has been shown that in the gasless high-power pulsed discharge with hot Cr target, plasma density is as high as 5 × 1018 m−3 at a pulsed power density of 1430 W/cm2, while the electron temperature drops to values below 1 eV.

BASIC PLASMA FEATURES OF PLANAR JET FORMED BY CAPACITIVE RF DISCHARGE IN ATMOSPHERE PRESSURE ARGON

Upgraded method of determining basic parameters of weakly ionized plasma by means of photometric study of bremsstrahlung emission continuum in visible spectrum range is described. Time-averaged spatial distributions of electron temperature and density in planar plasma jet formed by capacitive RF discharge in atmosphere pressure argon at the discharge glow in a low-current α-mode are experimentally obtained.

Numerical simulation of thermochemically non-equilibrium inductively coupled plasmas under different operating parameters

A thermochemical non-equilibrium model for inductively coupled plasmas (ICPs) has been utilized to investigate the effect of different operating parameters. The effects of operating parameters, including the injection mass flow rate, input power, operating pressure, and induction frequency, are studied in this manuscript. The spatial distributions of electron temperature, plasma velocity, and chemical particles fields are discussed under different operating conditions. The simulation results show that the spatial characteristics of ICP torch have a strong relationship with the variation of operating parameters, especially the pressure. However, the induction frequency over the range investigated is proved to have little significant effect on the distributions of plasma fields. This numerical model is helpful to determine the optimum conditions for the generation of the desired plasma.

Discharge parameters and plasma characterization in a dc magnetron with liquid Cu target

The magnetron discharge with uncooled Cu target has been investigated in a wide range of parameters (magnetic field, power, Ar pressure). The evolution of discharge voltage and current has been measured yielding the transition time to stable gasless self-sputtering regime of 175 s at 2.5 kW total power. I–V curves for the solid- and liquid-target magnetron discharge have been obtained, and the magnetic field magnitude has been optimized to ensure both highest attainable power density (600 W/cm2) and high discharge voltage (∼ 800 V) for the best sputtering efficiency. The spatial distributions of electron temperature and plasma density were systematically measured at different power values spanning from cold solid target to completely molten one. It has been shown that in the transition region plasma density grows unevenly with discharge power. Eventually, maximum densities of around 3 × 1011 cm−3 were recorded 5 cm away from the target. In the gasless self-sputtering mode, the deposition rate at 26 cm above the target increased 40-fold as compared to solid target performance under the same power conditions.

Emission Studies of Silicon Plasma Produced by a Nd: YAG Laser

In the present experimental work emission studies of silicon (Si) plasma produced by the fundamental (1064 nm) and second (532 nm) harmonics of a Nd: YAG laser are studied. The electron temperature measurements have been estimated using the Boltzmann plot method. The electron temperature as a function of laser irradiance (2 × 1010 to 6.5 × 1010 W/cm2) ranges from 11290 to 14120 K (for fundamental), and 11660 to 13750 K (for second) laser respectively. The electron number density is calculated using the Stark broadening profile of 288.15 nm (3p4s 1P1 → 3s 23p 2 1D2) transition. The electron number density as a function of laser irradiance ranges from 2.20 × 10 16 to 1.55 × 1017/cm3(for fundamental) and 1.09 × 1016 to 1.80 × 1017/cm3(for second) laser respectively. The spatial distribution of electron temperature and electron number density shows the same decreasing trend up to 2.0 mm from the target surface (0.05 mm). It is observed that electron temperature and number density increase as laser irradiance is increased. In addition the inverse bremsstrahlung absorption coefficient has been estimated. Variation of these plasma parameters (electron temperature and number density) along with variation of distances in the direction of propagation of the plasma plume have also been investigated.

RF plasma generation in the chamber with the conducting walls

This work is devoted to study of inductively coupled RF discharge within a metal chamber with a diameter of about 1 m and a length of about 2 m in argon gas (RF frequency is 5.28 MHz). The spatial distributions of electron temperature and density depending on the magnetic induction (from 0 to 0.2 T), plasma-forming gas pressure (0.1 − 10 mTorr) and RF power absorbed in the plasma are presented. For fixed gas pressure (6 mTorr) electron temperature decrease with increasing of magnetic field was found.

Investigations on spatial distribution of low temperature plasma parameters using NiCr wire probe diagnostic

This study investigated the workability of a NiCr wire probe diagnostic under low temperature plasma operating conditions. The aim of the work was to design and fabricate a triple Langmuir probe with NiCr alloy for measurements in low temperature rf plasmas. The spatial distribution of electron temperature and number density were evaluated at different filling pressures in the range of 0.2–0.4mbar and rf powers in the range of 200–400W. The probe data revealed a linear increase in temperature and electron number density with rf power along the chamber centerline, whereas an inverse relationship was found between the given plasma parameters and filling gas pressure. The spatial distribution measurements showed a decreasing trend in plasma parameters at positions away from the chamber centerline. The probe I–V characteristics curve revealed a change in polarity of probe potential with an increase in current supply from the plasma discharge to the probe. Initially, the potential difference raised from highly negative values to zero volt, thereafter started increasing positively. It is found that the response of NiCr alloy as probe material was appreciably good under the proposed operating conditions.

Spectroscopic studies of magnesium plasma produced by fundamental and second harmonics of Nd:YAG laser

In the present experimental work, laser induced magnesium plasma has been characterized using plasma parameters. The plasma has been generated by the fundamental (1064 nm) and second harmonics (532 nm) of Nd:YAG laser. The plasma parameters such as electron temperature and electron number density have been extracted using Boltzmann plot method and Stark broadened line profile, respectively. The laser irradiance dependence and spatial behavior of electron temperature and number density in laser induced magnesium plasma have been studied. The electron temperature as a function of laser irradiance (0.5 to 6.5 GW/cm2) ranges from (9.16–10.37) × 103 K and (8.5–10.1)× 103 K, and electron number density from (0.99–1.08) × 1016 cm−3 and (1.04–1.22) × 1016cm−3 for 1064 and 532 nm, respectively. These parameters exhibit fast increase at low laser irradiance and slow increase at high irradiance. The spatial distribution of electron temperature and electron number density shows same decreasing trend up to 2.25 mm from the target surface. The electron temperature and number density decrease from (9.5–8.6) × 103 K, (1.27–1.15) × 1016cm−3 and (10.56–8.85)× 103 K, (1.08–0.99) × 1016 cm−3 for 532 nm and 1064 nm laser ablation wavelengths, respectively.

Investigation of a polychromatic tomography method for the extraction of the three-dimensional spatial structure of implosion core plasmas

A spectroscopic method has been developed to extract the three-dimentional spatial structure (i.e., spatial distribution of electron temperature and density) of inertial confinement fusion implosion cores based on the analysis of space-resolved spectra from a tracer element recorded along three quasi-orthogonal lines of sight. We discuss a spectral model that computes space-resolved spectra for a given spatial structure. This model is then combined with a multi-objective search and optimization technique driven by a Pareto genetic algorithm to perform the inversion and to extract the spatial structure of the implosion core from a simultaneous and self-consistent analysis of a set of space-resolved spectra. This method is investigated with a series of synthetic data test cases to explore its reliability, requirements, and limitations. We have found a constraint parameter Pconst such that the method is robust and the extracted spatial structure is reliable when Pconst> 1. The idea of polychromatic tomography is general and has potential to extract the spatial structure of other laboratory high energy-density plasmas.

Spatial distribution of electron temperature and ion density in laser induced ruby (Al2O3:Cr3+) plasma using Langmuir probe

The investigation of laser produced ruby (Al2O3:Cr3+) plasma using a planar copper Langmuir probe is reported in the present paper. The ruby plasma was produced by focusing a high power Q-switched Nd:YAG laser on ruby target in a vacuum chamber at a base pressure of ∼ 10−5 mbar. The effect of probe distance on electron and ion time of flight (TOF) signals were studied. Twin peaks were observed for both ions as well as electron signal, confirming the two velocity components for both these species. A triple peak structure was also observed in case of electron TOF signal due to re-splitting of second peak at 50 and 60 mm probe distance. The electron temperature was estimated using characteristic I-V curve of Langmuir probe. It was found to decay exponentially from 16.0 eV to 4.5 eV with increase in distance from 5 mm to 80 mm w.r.t. target. The ion density was found to first increase from 1.2 × 1012 cm−3 to 1.0 × 1013cm−3 upto 40 mm, and then dropped down to 1.6 × 1012cm−3 at 50 mm and finally shows steady behavior.

激光诱导铝合金E414d等离子体电子温度的空间分布

激光诱导铝合金E414d等离子体电子温度的空间分布

New Compact and Time-Efficient Reliability Physics Model for p-Type Metal–Oxide–Semiconductor Field-Effect Transistors

In this paper, we present a new compact and time-efficient reliability physics model of drain, substrate, and gate currents for p-type metal–oxide–semiconductor field-effect transistors (pMOSFETs). The pre-stress drain current and channel electric field are first calculated, and the spatial distribution of electron temperature along the channel is then derived using a simplified energy balance equation. Having calculated the nonlocal impact ionization coefficient and electron temperature, and modified the lucky-electron concept, the nonlocal electron substrate and gate currents can be derived. We use an oxide-trapping mechanism for calculating the spatial distribution of oxide-trapping charges, which are substituted into the damaged pMOSFETs drain current model; then we can model the hot-carrier-damaged drain current. This model is a time-saving computer-aided-design (CAD) model and is physics transparent for pMOSFETs.

Construction and Plasma Initiation of the Tokamak-Helical Hybrid Device TOKASTAR-2

TOKASTAR, a hybrid magnetic configuration between tokamak and stellarator, has been proposed for the study of magnetic confinement optimization. The construction of the small device named TOKASTAR-2 was started in April 2008, and completed in March 2009. As a preliminary experiment, spatial distribution of electron temperature (Te) and electron density (ne) are measured in a simple toroidal magnetic field configuration. Initial ECH plasmas with Te ∼ 10 eV, ne ∼ 1016 m−3 are confirmed. In the preliminary experiment of ohmic heating plasma production, plasma current (Ip) of 25 A is observed. The plasma equilibrium is calculated by the TOSCA code, and the magnetic flux surface and optimal vertical field coil currents are clarified for the future experiment.

Electron Substrate and Gate Current Modeling for Single-Drain Buried-Channel p-Type Metal–Oxide–Semiconductor Field-Effect Transistors Including Tunneling Mechanisms

A model of nonlocal electron substrate and gate currents is presented for single-drain (SD) buried-channel (BC) p-type metal–oxide–semiconductor field-effect transistors (pMOSFETs). A nonlocal impact ionization coefficient with characteristic length dependence both in the exponential term and the pre-exponential factor is used in the electron substrate current model. The gate current model is developed by originating a modified lucky electron concept that includes quantum-mechanical tunneling effects in parallel. The channel electric field is first calculated by using an analytical pseudo-two-dimensional MOSFET model, and the spatial distribution of electron temperature along the channel is then derived using a simplified energy balance equation. Having calculated the nonlocal impact ionization coefficient and electron temperature, and modified the lucky electron concept, the nonlocal electron substrate and gate currents can be derived. This model is a time-saving computer-aided-design (CAD) model and is physics transparent for SD BC pMOSFETs.