Decrease In Electron Temperature Research Articles

Theoretical study of particle and energy balance equations in locally bounded plasmas

In this study, new particle and energy balance equations have been developed to predict the electron temperature and density in locally bounded plasmas. Classical particle and energy balance equations assume that all plasma within a reactor is completely confined only by the reactor walls. However, in industrial plasma reactors for semiconductor manufacturing, the plasma is partially confined by internal reactor structures. We predict the effect of the open boundary area ( ) and ion escape velocity ( ) on electron temperature and density by developing new particle and energy balance equations. Theoretically, we found a low ion escape velocity ( / ) and high open boundary area ( ) to result in an approximately 38% increase in electron density and an 8% decrease in electron temperature compared to values in a fully bounded reactor. Additionally, we suggest that the velocity of ions passing through the open boundary should exceed under the condition .

Kinetics of optical phonons and DP depolarization of spins in drift transport: Hot carrier spin effect in semiconductors

<p>Spin-<strong>c</strong>onserving transport of carriers is an essential requirement for the practical semiconductor-based spintronic devices. Kinetics of optical phonons and Dyakonov-Perel (DP) depolarization of spins in drift transport in semiconductor gallium arsenide (GaAs) is theoretically investigated<strong>. </strong>We consider electrons in <em>n</em>-type bulk GaAs subjected to a strong electric field, where the electron distribution is assumed to be drifted Maxwellian. The momentum drift of this distribution results in the enhanced drift velocity, and electrons with the corresponding energy emit optical hot phonons in the drifting process. The hot phonons are incorporated via the longitudinal polar optical phonon (POP) mechanism in the momentum relaxation. It is found that a finite phonon lifetime can reduce the momentum relaxation rate, which results in a delay in the runaway to higher fields, where the effect increases with the electron density. The electron spin is found to relax with the DP relaxation frequencies, and the DP spin lifetimes are found to decrease with increasing the drift field. However, a high field completely depolarizes the electron spin due to an increase of the DP spin precession frequency of the hot electrons in the POP scattering process. It is also found that the DP spin precession frequency decreases with decreasing electron temperature or increasing electron density in the moderate range. However, the findings resulting from this investigation demonstrate the hot carrier effect in the spin transport in semiconductors. The results are discussed in comparison with those obtained in earlier experimental and theoretical studies with different approaches.</p>

Excitation of ion acoustic solitary waves and shock waves in decaying plasma between biased parallel-plate electrodes

In this study, we explore the excitation of ion acoustic solitary waves and shock waves in a decaying plasma confined between biased parallel-plate electrodes using one-dimensional particle-in-cell simulations. Our findings demonstrate that the oscillating electric field at the sheath edge generates a sequence of ion acoustic solitary waves, which exhibit characteristics consistent with the Korteweg–de Vries (KdV) equations. We observe that as the electron temperature decreases, the intervals between adjacent wave pulses shorten progressively, leading to the eventual formation of a coherent shock wave structure. These findings highlight the critical role of kinetic simulations in elucidating the dynamics of plasma decay processes.

Collisional-Radiative modeling of unresolved transition array spectra near 200 Å from W17+-W25+ emissions for diagnostics of ITER edge plasma

Tungsten (W) is one of the major impurities in ITER and future DEMO reactors. However,diagnosing the ion density, temperature, and spatial distribution of tungsten ions in intermediate charge states, such as W8+-W27+, is difficult because of the lack of spectral line data. In this study, we observed a tungsten Unresolved Transition Array (UTA) spectrum, which has a pseudo-continuum structure, around W20+ in the Extreme Ultraviolet wavelength region in the Large Helical Device (LHD). We conducted Collisional-Radiative (CR) modeling for W17+-W25+. Two pseudo-continuum peaks corresponding to 5 s-5p transition and transition between doubly excited states of 5 s2-5s5p, are strongly emitted around 200 Å for each ion. The synthesized spectrum of W17+-W25+ ions reproduced the observed LHD spectrum near 200 Å. From the electron temperature dependence of the UTA spectral shape, the UTA shifted toward longer wavelength region with several pseudo-continuum peaks appearing for ions in lower charge states, with decreasing electron temperature from 0.4 keV to 0.2 keV. This result qualitatively explained the observed time evolution of the spectrum.

TECXY simulations of the power exhaust in the multi-impurity plasma of DTT reactor

Reduction of the heat load to plasma-facing components is a crucial problem for future fusion reactors like Divertor Test Tokamak (DTT). Mitigation of the power load via increased plasma radiation with the use of puffed ions of impurities would be one way to mitigate power in the scrape-off layer. This paper presents a numerical investigation of the impact of seeded impurities on the radiation pattern and the power load to the divertor plates of the high-field DTT reactor in the single null (SN) configuration. The simulations have been done with the use of the TECXY code, which solves multi-species plasma transport equations for multiple impurity species simultaneously and all associated ionization stages in a two-dimensional poloidal geometry. TECXY represents the model of plasma transport in the scrape-off layer region by a classical set of transport equations of multi-species plasma derived by Braginskii. The paper aims to compare the mitigation capabilities of neon and argon impurities seeded in the plasma of the DTT device and to obtain a significant energy flux reduction to the target plate at the smallest possible impurity concentration. Performed investigations showed the effects of neon and argon impurities seeding separately for constant electron density at the separatrix. It has been found that the decrease in electron temperature on the divertor plates up to 3 eV at the outer and the inner divertor plates and the peak power load below 15 MW m−2 at the outer divertor plate can be achieved with argon seeding and much lower impurity concentration than that in the case of neon impurity seeding. Studies have shown the complexity of the effect of neon and argon impurities on the boundary plasma. It was found that the reduction of temperature and the power on both divertor plates was the most effective for the high upstream plasma densities. The results show also that diffusive perpendicular transport strongly affects impurity radiation and thus plasma condition at divertor plates.

Experimental studies of H2/Ar plasma in a cylindrical inductive discharge with an expansion region

Abstract The electrical parameters of H2/Ar plasma in a cylindrical inductive discharge with an expansion region are investigated by a Langmuir probe, where Ar fractions range from 0% to 100%. The influence of gas composition and pressure on electron density, the effective electron temperature and the electron energy probability functions (EEPFs) at different spatial positions are present. In driver region, with the introduction of a small amount of Ar at 0.3 Pa, there is a rapid increase in electron density accompanied by a decrease in the effective electron temperature. Additionally, the shape of the EEPF transitions from a three-temperature distribution to a bi-Maxwellian distribution due to an increase in electron–electron collision. However, this phenomenon resulting from the changes in gas composition vanishes at 5 Pa due to the prior depletion of energetic electrons caused by the increase in pressure during hydrogen discharge. The EEPFs for the total energy in expansion region is coincident to these in the driver region at 0.3 Pa, as do the patterns of electron density variation between these two regions for differing Ar fractions. At 5 Pa, as the discharge transitions from H2 to Ar, the EEPFs evolved from a bi-Maxwellian distribution with pronounced low energy electrons to a Maxwellian distribution in expansion region. This evolve may be attributed to a reduction in molecular vibrational excitation reactions of electrons during transport and the transition from localized electron dynamics in hydrogen discharge to non-localized electron dynamics in argon discharge. In order to validate the experimental results, we use the COMSOL simulation software to calculate electrical parameters under the same conditions. The evolution and spatial distribution of the electrical parameters of the simulation results agree well with the trend of the experimental results.

Abnormal behavior of the plasma potential in an inductively coupled plasma with a DC-biased grid

Abstract The formation of the plasma potential and the generation mechanism of very low electron temperature plasma are investigated in an inductively coupled plasma with a DC biased grid. The electron temperature is controlled from 2.4 eV to 0.2 eV according to the grid voltage (10 V to −40 V). Interestingly, when the grid voltage is negatively biased, the electron temperature decreases and the plasma potential decreases with the grid voltage, but then increases below −10 V which is abnormal. This behavior of the plasma potential is abnormal since the plasma potential is generally proportional to the electron temperature. The main reason for the abnormal increase of the plasma potential is the difference in the flux of electrons and ions below the grid. As the grid is negatively biased, the electron flux is greatly reduced compared to the ion flux, leading to an increase in plasma potential. After −20 V, the plasma potential saturates, because although the number of electrons entering the grid decreases, the electron flux is maintained by secondary electrons generated in the grid mesh. This abnormal increase in plasma potential decreases with pressure. An increase in plasma potential with gas species is also observed. The same behavior is observed for Ar, He, and N2 gases. The abnormal behavior of the plasma potential is explained with the current continuity.

Internal energy distributions of BeH, BeD, and BeT molecules created during chemically assisted physical sputtering in JET tokamak plasma

We present here the results of the spectroscopic analysis of the high-resolution visible spectra of beryllium hydride and its isotopologues (BeH, BeD, and BeT), produced during plasma–surface interactions during limiter and divertor JET-ILW (ITER-like Wall) pulses. The hydride production, being an important part of the wall erosion via chemical-assisted physical sputtering, shows visible dependence on plasma and wall conditions, and also on the isotope content of the plasma. This work shows that this dependence is also true for the molecular energy distributions, parameterized by rotational and vibrational temperatures. During the increase in the vessel wall temperature by 350 K, with constant plasma parameters, rotational temperature of the excited BeD molecules increases by 500 K, whereas the vibrational temperature decreases by 400 K. Another experiment was the scan of the integrated edge density, during which electron density increases with the increasing edge density, and electron temperature decreases. During that scan for BeD, Trot decreases by 300 K and Tvib by 400 K over the change in an integrated edge density of ΔNe=+8×1018 m−2. Both trends were compared with the trends in other isotopes, and the qualitative results are similar, but the limited data available restrict the possibility of a full quantitative comparison. To simplify the comparison between the results presented here and other experiments or modeling data, and also to check the comparability of the pulses performed in different isotopes, the Be ion line ratios are used as benchmarks of the edge plasma condition.

Plasma electron characterization in electron chemical vapor deposition

Recently, a novel approach of depositing metallic films with chemical vapor deposition (CVD), using plasma electrons as reducing agents, has been presented and is herein referred to as e-CVD. By applying a positive substrate bias to the substrate holder, plasma electrons are drawn to the surface of the substrate, where the film growth occurs. In this work, we have characterized the electron flux at the substrate position in terms of energy and number density as well as the plasma potential and floating potential when maintaining an unbiased and a positively biased substrate. The measurements were performed using a modified radio frequency Sobolewski probe to overcome issues due to the coating of conventional electrostatic probes. The plasma was generated using a DC hollow cathode plasma discharge at various discharge powers and operated with and without precursor gas. The results show that the electron density is typically around 1016 m−3 and increases with plasma power. With a precursor, an increase in the substrate bias shows a trend of increasing electron density. The electron temperature does not change much without precursor gas and is found in the range of 0.3–1.1 eV. Introducing a precursor gas to the vacuum chamber shows an increase in the electron temperature to a range of 1–5 eV and with a trend of decreasing electron temperature as a function of discharge power. From the values of the plasma potential and the substrate bias potential, we were able to calculate the potential difference between the plasma and the substrate, giving us insight into what charge carriers are expected at the substrate under different process conditions.

A harmonic method for measuring electron temperature and ion density using an asymmetric double probe

The harmonic method using a symmetric double probe was developed for measuring electron temperature and ion density Oh et al (2012 Meas. Sci. Technol. 23 085001). When an alternating voltage is applied to the symmetric double probe where the two areas of the collector for current collection are equal, the fundamental frequency current and third harmonic currents are generated. The electron temperature and ion density are obtained by measuring the fundamental frequency current and the third harmonic current. However, it is observed that the third harmonic current can rapidly decrease to the level of base noise when the ratio of the applied voltage to the electron temperature decreases. Therefore, it is necessary to increase the harmonic currents generated to improve measurement accuracy for electron temperature and ion density. In this paper, a harmonic method using an asymmetric double probe with different collection areas is proposed to measure electron temperature and ion density. By using the double probe with different collector area, the fundamental frequency current and the second harmonic current are generated. In the proposed method, the electron temperature and ion density are obtained by measuring the fundamental frequency current and the second harmonic current. It is found that the accuracy of the electron temperature can be improved by measuring the second harmonic rather than measuring the third harmonic current. For quantitative comparison, the electron temperature and ion density obtained by the proposed method were compared with the electron temperature and electron density obtained by the measurement electron energy probability function, which showed good agreement between them in argon plasma at various conditions. In addition, it was experimentally verified that the electron temperature can be accurately measured even when the chamber is electrically insulated, and a dielectric layer is deposited on the collectors of the double probe, such as in the plasma process.

Investigation of the temperature of electrons in a glow discharge plasma at direct current Ar and Ar/C2H2

This paper presents the results of the study of the electron temperature in argon and argon-acetylene plasma of DC glow discharge. The optical-emission method was used to determine the main parameter of the complex plasma. The dependence of the electron temperature on the operating pressure, voltage, and discharge time was determined from the intensity of spectral lines. The source voltage was varied from 1 kV to 1.5 kV, and the pressure was maintained between 0.1-1 torr. As a time-dependent function, the electron temperature was calculated every 20 seconds during a 200-second discharge. The results showed that in argon plasma, as the pressure increases, the electron temperature decreases up to a pressure value of 0.4 torr, subsequent increase leads to an increase in temperature. Also, with the increase in source voltage, a decrease in electron temperature within the error limits is observed. In addition, in dust plasma (PECVD in Ar-C2H2), the electron temperature as a function of pressure and source voltage showed a trend similar to that observed in argon plasma. However, the electron temperature in dust plasma increases as a function of time at the initial moment, after which it decreases sharply with time.

First Experiments on Reduction the Heat Load on the Divertor Plates of the Globus-M2 Tokamak Using Nitrogen Seeding and Their Comparison with Simulation Results

At the compact spherical Globus-M2 tokamak, a series of experiments was conducted to study theeffect of the injection of nitrogen on the discharge parameters. The experiments were carried out in dischargesin deuterium in the divertor configuration, and the auxiliary heating was performed by deuteriumneutral beam injection. During the nitrogen seeding, a substantial decrease in electron temperature near thedivertor was recorded as well as a sharp decrease of the heat flux onto the divertor plate, while the density andtemperature of the main plasma changed insignificantly. Simulations by the SOLPS-ITER showed a satisfactoryagreement with the experiment.

Numerical Study of Ar/O2 Discharge Properties Influenced by Small Secondary Electron Emission in Dual-Frequency Atmospheric Pressure Discharge

A one-dimensional fluid model was employed to investigate the influence of the small secondary electron emission (SEE) coefficient on the characteristic properties of an Ar/O2 gas discharge at atmospheric pressure driven by a dual frequency source. The study includes basic physical quantities such as particle density, electron temperature, the electron heating mechanism, and energy loss. The research results illustrate that with an increase in the secondary electron emission coefficient, the electron density increases, while electron temperature and electric field decrease. The densities of various particles increase to different degrees, except for the metastable O2* molecule and the O atom. The density of the metastable O2* molecule and the density of the O atom are hardly affected by the SEE coefficient; however, the time required for both to reach steady state decreases. The time required for the electron density to reach steady state increases. Electron heating and energy loss increase to varying degrees when the SEE coefficient changes from 0.001 to 0.01.

Influence of plasma parameters on low-k SiCOH film grown by plasma-enhanced chemical vapor deposition using dimethyldimethoxysilane

Here, we report the influence of the electron density and the electron temperature on the reduction of dielectric constant in the SiCOH thin film using dimethyldimethoxysilane (DMDMS) as a function of pressure. The measured electron density and electron temperature decreased as increasing the pressure. The decrease in the measured electron density with increasing pressure can be attributed to local electron kinetics. Moreover, the decreasing electron temperature is caused by increased inelastic collisions between electrons and neutral species in the chamber. It is identified that CH3 radicals are less dissociated from DMDMS molecular at higher pressure by a quadrupole mass spectroscopy. As increasing pressure, the increase of the Si–CH3 bonds in SiCOH thin films is confirmed by Fourier transform infrared spectroscopy. As a result, the dielectric constant and refractive index of the SiCOH films are reduced at low electron density and electron temperature.

Study of the evolution of pulsed plasma under an external longitudinal magnetic field

An experimental study on the role of an external longitudinal magnetic field on the characteristics changes of pulsed plasma stream, produced in argon medium, is carried out at different time spans of its evolution. The spectroscopic observations are time integrated and are carried out at different times of plasma formation for pulsed discharge. This study gives insights into the recombination and diffusion phase of the plasma species in the presence of the magnetic field. The transition of plasma species from a dominant recombination phase to a diffusional phase is well revealed by the density profile during the time evolution. Moreover, the decrease in electron temperature and the increase in electron excitation temperature explain the energy transfer to electrons due to metastable quenching, and the system gradually approaches equilibrium. The magnetic field also affects the transitions of the ionized argon population between different energy levels. It is found that faster decay occurs for transitions of different plasma species to non-metastable states, while the populations of metastable states exist for a longer time. In addition, the time-resolved morphology changes of the plasma stream are also observed by high speed imaging, which shows the flow structure of the plasma stream at different time frames. The imaging of the plasma stream evolution shows the initial ejection of the plasma sheet from the electrode assembly, its detachment, the steady flow, and gradually its nature of dying out.

High-speed plasma diagnostics based on the floating harmonic method in inductively coupled plasma and pulsed plasma

Abstract The floating harmonic method is a diagnostic technique for obtaining plasma parameters, such as ion density and electron temperature, by applying a sinusoidal voltage to a floating probe. The typically applied frequency is in the kilohertz range. This method has been widely used in plasma diagnostics of semiconductor processes due to its robustness to RF fluctuations and fast measurement speed. However, recently, pulsed plasma has become common in semiconductor processes. As the plasma sheath is analyzed with a high-time-resolution diagnostic method such as phase-resolved optical emission spectroscopy, the development of high-speed plasma diagnostic techniques has become increasingly important. In this study, we investigated high-speed plasma diagnostic measurements based on the floating harmonic method. When the frequency of the voltage applied to the floating probe increases up to 1 MHz, the electron temperature can be underestimated due to the currents flowing through the capacitive sheath and the ceramic sleeve of the probe. We found that the displacement current of the probe sheath increases rapidly compared to the conduction current as the plasma density and electron temperature decrease. We also removed the additional harmonic currents flowing through the ceramic sleeve via two approaches. The plasma parameters obtained using the proposed method are in good agreement with the measurements performed using the floating harmonic method in the kilohertz range. Moreover, the electron temperature of the pulsed plasma was measured.

Study on characteristics of electron parameters on inert gas addition in a capacitively coupled SF6/O2 plasma

In this paper, characteristics of electron parameters of SF6/O2 and inert gas mixture in a capacitively coupled plasma were studied. Here, gases such as He, Ar, and Xe were added to SF6/O2 mixture and electron energy probability functions (EEPFs) were measured. The electron parameters were acquired, which agreed well with EEPF behaviors. Normally, the inert gas functioned as an electron source and the electron density tended to increase. When the inert gas ratio exceeded other gases, the effect of the mixture varied on each gas. He showed its unique behaviors with the increase in electron temperature. Ar and Xe showed consistent behaviors with increasing electron density and decreasing electron temperature as the inert gas proportion increases. Different behaviors of the electron parameters in inert gases can be explained by the complex contribution of electron attachment of SF6 and the ionization rate of each inert gas.

The Influence of the Magnetic Field on the Plasma Characteristics in Hollow Electrodes Discharge System

This work is an experimental study about the effects of gas pressure and magnetic field on plasma characteristics produced in an internal hollow electrodes discharge (HED) system. The results show that the breakdown voltage values increase with increasing the working pressure (especially with the presence of a magnetic field). The breakdown voltage depends on the p.d. product, where p is the gas pressure and d is the distance between the electrodes. While the values of current discharge decrease with the increase of the working pressure. The temperature of electron and the number density of electron are calculated from the Boltzmann method and the broadening of Stark, respectively. The results showed that the electron number density ( ) and plasma frequency ( ) increase with increasing the gas pressure, especially with the presence of a magnetic field, i.e. the plasma is more stable with the presence of magnetic field. While the electron temperature ( ) and Debye length ( ) decrease with increasing the gas pressure.

Influence of Cylindrical Electrode Configuration on Plasma Parameters in a Sputtering System

In the present work, the effect of the cylindrical configurations of the sputtering device electrodes on the plasma parameters (Debye length, electron temperature, electron density, plasma frequency) is studied. Also, the effect of the argon gas pressure on the discharge properties is examined with gas pressures of (0.08, 0.2, 0.4 and 0.6) Torr. The properties of the plasma are diagnosed by optical emission spectrometry. The spectroscopic method is adopted for examining the atomic spectra of argon emission. The electron temperature is determined by the Boltzmann method. While, the Stark-widening method was employed for calculating the electron number density. The voltage against current curves of the cylindrical sprayer discharges shows the voltage to be nearly constant with slight increase in current. An increase in pressure causes the cathode cascades to compress and the negative glow to become thinner and more luminous. Plasma properties such as electron temperature and Debye length decrease with increasing pressure, while electron number density and plasma frequency increase.

Performance Analysis of an Electron Cyclotron Resonance Thruster with Various Propellants

The performance of an electron cyclotron resonance thruster is analyzed for operation with argon, krypton, xenon, and water vapor to understand how mass utilization efficiency and frozen flow losses vary across propellant type. The device was operated from 20 to 220 W for flow rates of 0.06–0.4 mg/s. Thrust performance is measured using an inverted pendulum thrust stand, and plasma characteristics are measured using a retarding potential analyzer, ExB probe, Langmuir probe, and emissive probe. Specific impulse is generally found to decrease as the ratio of mass flow rate over power () increases. Probe measurements indicate that this trend is attributed to a combination of lower propellant mass utilization and decreased electron temperatures. The mass utilization efficiency is found to increase with the ratio of thruster length to ionization mean free path for all propellants; however, the data do not support existing theoretical scaling laws, and a more accurate empirical scaling law is proposed. The decrease in electron temperature with also drives an increase in the relative frozen flow losses, which are found to be about a factor of two higher for water propellant. Multiply charged ions did not constitute a significant fraction of the plume for the atomic species. Mass utilization efficiency and frozen flow losses describe the trends in the thrust efficiency but not the overall magnitude, which suggests that microwave coupling and diffusion to the walls are dominant loss processes.