Average Electron Temperature Research Articles

Characteristics of regular discharges in Uragan-3M torsatron

The Uragan-3M device is equipped with two antennas which are fed by RF power with the frequency below ion cyclotron. The frame antenna was used for pre-ionization and the three-half turn antenna makes plasma heating. In this experimental series, the radial profiles of C III, O V and C V optical line intensity and the second cyclotron harmonic emission are measured using a pulse-by-pulse technique. The results of these measurements and Biot–Savart calculations of the Uragan-3M magnetic configuration could be explained by the existence of a small central area with relatively high electron temperature and good plasma confinement surrounded by a zone where the electron temperature and confinement are worse. The relatively low average electron temperature and high RF power needed to sustain plasma are the consequences.

Measurement of the Polytropic Index During Solar Coronal Rain Using a Diagram of the Electron Density Distribution as a Function of Electron Temperature

A differential emission measure (DEM) method is used to evaluate the relationship of the electron density and temperature before and after a coronal rain event during an active sun over the period from 20:10 UT on October 6 to 02:10 on October 7, 2011. Observational data were obtained from SDO/AIA for six different extreme ultraviolet (EUV) spectral lines. 240 different coronal loops were analyzed during this time interval, and the average electron density and temperature were obtained using 171 {\AA} (Fe IX) and 193 {\AA} (Fe XII) filters. The relationship between the density and temperature made it possible to estimate the polytropic index in the solar corona before and after the coronal rain. The polytropic index after the termination of the coronal rain was estimated to be {\gamma} = 1.3{\pm}0.06, Which shows the usual thermodynamic properties of study-state coronal plasma. The polytropic index at the time of onset of the coronal rain was, however, estimated to be {\gamma} = 2.1{\pm}0.11, which indicates an unstable thermodynamic process, i.e., thermal instability. It is suggested that the coronal rain is the result of an unstable process, and the coronal plasma returns its stable state after the rain.

Statistical properties of the plasma fluctuations and turbulent cross-field fluxes in the outboard mid-plane scrape-off layer of Alcator C-Mod

The Alcator C-Mod mirror Langmuir probe diagnostic is used to characterize plasma fluctuations in the outboard mid-plane scrape-off layer (SOL). Ohmically heated L-mode plasmas with Greenwald fractions from 0.1 to 0.45 are analyzed. In plasmas with a low line-averaged core density, the radial profiles of the average electron density and temperature feature a two-scale structure with a strong gradient in the near-SOL and a weak gradient in the far-SOL. The relative fluctuation levels of the electron density are below 25% throughout the entire SOL and the fluctuation driven heat flux is dominated by plasma density fluctuations. In the plasma with the highest line-averaged core density, the radial profiles of the electron density and temperature feature only a single weak gradient length scale across the SOL. The plasma density at the limiter radius is approximately 10 times larger than in low-density discharges. The average electron temperature at the separatrix falls to approximately 30 eV while the magnitude of the relative temperature fluctuations increases with the line-averaged core plasma density. With increasing plasma density, the fluctuation-driven heat fluxes increase by more than one order of magnitude while retaining a relative fluctuation level of approximately 3. Even though the SOL is on average cooler than in low density discharges, large electron temperature fluctuations govern the turbulence driven heat flux towards the wall while contributions from density fluctuations and triple correlations contribute approximately 35% and 15%, respectively.

Axial Ring-Cusp Hybrid (ARCH) plasma discharge: an approach to highly efficient miniature-scale ion sources

The miniaturization of conventional direct-current ion sources is predominantly restricted by efficiency limitations associated with the increased surface area-to-volume ratio of smaller-scale discharge chambers—reducing the effective confinement length of the high-energy ‘primary’ electrons that is necessary for efficient plasma generation. The Axial Ring-Cusp Hybrid (ARCH) plasma discharge addresses this scaling limitation by using a new approach that combines magnetic and electrostatic confinement to decouple the primary and plasma electrons loss mechanisms. Simulated ion thruster performance measurements show that the ARCH discharge may be capable of achieving a discharge loss and a propellant mass utilization of 175 eV/ion and 0.87, respectively. These estimates are supported by full internal maps of the plasma properties, including the electron energy distribution function, inside the discharge chamber. The measurements show highly effective confinement of the primary electrons, high average plasma electron temperatures of ∼5 eV, and low plasma sheath potential relative to the anode—attributes generally found only in efficient conventional-scale discharges with good overall plasma confinement. As such, the new ARCH discharge design approach may allow miniature ion thrusters to achieve the performance and efficiency levels similar to those of highly efficient conventional ion thrusters.

Average electron temperature estimation of streamer discharge in ambient air.

The electron temperature of small streamer plasmas with low ionization degree is difficult to measure using existing diagnostic technologies such as Langmuir probe and laser Thomson scattering. In this report, we introduce a method of average electron temperature estimation based on the electron continuity equation. The equation includes a temporal derivative of electron density as the summation of diffusion current, drift current, and electron gain/loss events. In the considered example, the electron density is measured using the Rayleigh scattering while the currents and the rate coefficients of those events are functions of the electric field, electron collision frequency, and electron temperature. Therefore, once the electric field and collision frequency are either measured or estimated, the only unknown in the equation is the average electron temperature which can be solved. It was estimated that electron temperature in the streamer peaks at about 3.9 eV for the given example.

Multi-wavelength campaign on NCG 7469

We conducted a multi-wavelength 6-month campaign to observe the Seyfert Galaxy NGC 7469, using the space-based observatories HST, Swift, XMM-Newton and NuSTAR. We report the results of the spectral analysis of the seven simultaneous XMM-Newton and NuSTAR observations. The source shows significant flux variability within each observation, but the average flux is less variable among the different pointings of our campaign. Our spectral analysis reveals a prominent narrow neutral Fe Kα emission line in all the spectra and weaker contributions from Fe Kβ, neutral Ni Kα, and ionized iron. We find no evidence for variability or relativistic effects acting on the emission lines, which indicates that they originate from distant material. In the joint analysis of XMM-Newton and NuSTAR data, a constant photon index is found (Γ = 1.78 ± 0.02) together with a high energy cut-off Ecut = 170−40+60 keV. Adopting a self-consistent Comptonization model, these values correspond to an average coronal electron temperature of kT = 45−12+15 keV and, assuming a spherical geometry, an optical depth τ = 2.6 ± 0.9. The reflection component is consistent with being constant and the reflection fraction is in the range R = 0.3−0.6. A prominent soft excess dominates the spectra below 4 keV. This is best fit with a second Comptonization component, arising from a warm corona with an average kT = 0.67 ± 0.03 keV and a corresponding optical depth τ = 9.2 ± 0.2.

Influence of catalyst packing configuration on the discharge characteristics of dielectric barrier discharge reactors: A numerical investigation

A two-dimensional numerical fluid model is developed for studying the influence of packing configurations on dielectric barrier discharge (DBD) characteristics. Discharge current profiles and time averaged electric field strength, electron number density, and electron temperature distributions are compared for the three DBD configurations, plain DBD with no packing, partially packed DBD, and fully packed DBD. The results show that a strong change in discharge behaviour occurs when a DBD is fully packed as compared to partial packing or no packing. While the average electric field strength and electron temperature of a fully packed DBD are higher relative to the other DBD configurations, the average electron density is substantially lower and may impede the DBD reactor performance under certain operating conditions. Possible scenarios of the synergistic effect of the combination of plasma with catalysis are also discussed.

Effect of parallel magnetic field on repetitively unipolar nanosecond pulsed dielectric barrier discharge under different pulse repetition frequencies

A magnetic field, with the direction parallel to the electric field, is applied to the repetitively unipolar positive nanosecond pulsed dielectric barrier discharge. The effect of the parallel magnetic field on the plasma generated between two parallel-plate electrodes in quiescent air is experimentally studied under different pulse repetition frequencies (PRFs). It is indicated that only the current pulse in the rising front of the voltage pulse occurs, and the value of the current is increased by the parallel magnetic field under different PRFs. The discharge uniformity is improved with the decrease in PRF, and this phenomenon is also observed in the discharge with the parallel magnetic field. By using the line-ratio technique of optical emission spectra, it is found that the average electron density and electron temperature under the considered PRFs are both increased when the parallel magnetic field is applied. The incremental degree of average electron density is basically the same under the considered PRFs, while the incremental degree of electron temperature under the higher-PRFs is larger than that under the lower-PRFs. All the above phenomena are explained by the effect of parallel magnetic field on diffusion and dissipation of electrons.

Influence of dust particles on DC glow discharge plasma

The effect of dust particles on DC glow discharge plasma parameters is studied numerically through the development of a self-consistent model based on the extended fluid approach. The orbital motion limited theory and collision enhanced collection approximation are employed to describe the charging processes of dust particles with various sizes and densities. The uniform distribution of dust particles in plasma and the instantaneous charging process were assumed during simulations. The influence of dust particle size rd and density Nd on gas discharge and dust particle parameters is investigated systematically. It is shown that the plasma parameters can be affected obviously by the dust particles. The increase in the values of rd and Nd leads to the decrease in the dust particle charge number, electron, and ion density. Meanwhile, the appearance of dust particles leads to an obvious increase in the averaged plasma electric field and electron temperature to sustain the discharge in the dust region. The dust particles are proven to be a very efficient way to artificially manipulate gas discharge parameters.

Diagnostic of capacitively coupled radio frequency plasma from electrical discharge characteristics: comparison with optical emission spectroscopy and fluid model simulation

The capacitively coupled radio frequency (CCRF) plasma has been widely used in various fields. In some cases, it requires us to estimate the range of key plasma parameters simpler and quicker in order to understand the behavior in plasma. In this paper, a glass vacuum chamber and a pair of plate electrodes were designed and fabricated, using 13.56 MHz radio frequency (RF) discharge technology to ionize the working gas of Ar. This discharge was mathematically described with equivalent circuit model. The discharge voltage and current of the plasma were measured at different pressures and different powers. Based on the capacitively coupled homogeneous discharge model, the equivalent circuit and the analytical formula were established. The plasma density and temperature were calculated by using the equivalent impedance principle and energy balance equation. The experimental results show that when RF discharge power is 50–300 W and pressure is 25–250 Pa, the average electron temperature is about 1.7–2.1 eV and the average electron density is about 0.5 × 1017–3.6 × 1017 m−3. Agreement was found when the results were compared to those given by optical emission spectroscopy and COMSOL simulation.

Estimation of Beam and Plasma Parameters for Electron Beam Transport in Ion-Focused Regime

This paper presents the analysis of cylindrical electron beam and beam-impact-generated plasma using particle-in-cell simulation code VSim 6.2 at different operating conditions. The transient plasma parameters, such as, beam density, charge neutralization factor, space charge potential, ionization time, beam compression, and plasma electron temperature, have been estimated and analyzed for a 40-keV, 10–100-A electron beam propagating in argon gas-filled drift space at different operating pressures. These parameters are difficult to be measured experimentally. The evaluated charge-neutralizing factor has been found dynamic in space and time, which is maximum at the beam envelope. The voltage profile of space charge potential required for effective electron beam propagation approaches zero due to formation of the plasma in the order of ionization time. The estimated average plasma electron temperature has been found to be less than ~1 eV, which is less damaging for interaction structure of the plasma-assisted microwave sources. It has been observed that an optimum pressure limit needs to be maintained inside the drift space to prevent the loss of electron beam due to instabilities resulting in excessive collisions with the drift space walls.

Characteristics of gas-liquid diaphragm discharge and its application on decolorization of brilliant red B in aqueous solution

A simple gas-liquid diaphragm discharge reactor was designed and characteristics of the discharge and its application on decolorization of brilliant red B in an aqueous solution were investigated. The results showed that strong oxidizing agents such as ·OH and ·O radicals were generated. Average electron temperature of the discharge was 0.72 eV, 1.15 eV and 0.83 eV with air, oxygen and argon as the discharge gas, respectively. Solution pH and conductivity changed little when oxygen or argon was used as the discharge gas; however, these two parameters changed significantly when the discharge was performed in air. During the discharge treatment, the characteristic absorption peaks of brilliant red B gradually decreased where the decolorization followed the first-order kinetics. With 10 min of discharge, the decolorization of brilliant red B (30 mg L−1) can reach 96%, 81% and 62% in the cases of oxygen, argon and air, respectively. The analysis of by-products showed that the brilliant red B molecule can be effectively destroyed in this discharge mode.

Electron heating and energy inventory during asymmetric reconnection in a laboratory plasma

AbstractElectron heating and the energy inventory during asymmetric reconnection are studied in the laboratory plasma with a density ratio of about 8 across the current sheet. Features of asymmetric reconnection such as the large density gradients near the low‐density side separatrices, asymmetric in‐plane electric field, and bipolar out‐of‐plane magnetic field are observed. Unlike the symmetric case, electrons are also heated near the low‐density side separatrices. The measured parallel electric field may explain the observed electron heating. Although large fluctuations driven by lower hybrid drift instabilities are also observed near the low‐density side separatrices, laboratory measurements and numerical simulations reported here suggest that they do not play a major role in electron energization. The average electron temperature increase in the exhaust region is proportional to the incoming magnetic energy per an electron/ion pair but exceeds scalings of the previous space observations. This discrepancy is explained by differences in the boundary condition and system size. The profile of electron energy gain from the electric field shows that there is additional electron energy gain associated with the electron diamagnetic current besides a large energy gain near the X line. This additional energy gain increases electron enthalpy, not the electron temperature. Finally, a quantitative analysis of the energy inventory during asymmetric reconnection is conducted. Unlike the symmetric case where the ion energy gain is about twice more than the electron energy gain, electrons and ions obtain a similar amount of energy during asymmetric reconnection.

Spectral evolution of soft x-ray emission from optically thin, high electron temperature platinum plasmas

The soft x-ray spectra of heavy element plasmas are frequently dominated by unresolved transition array (UTA) emission. We describe the spectral evolution of an intense UTA under optically thin conditions in platinum plasmas. The UTA was observed to have a peak wavelength around 4.6 nm at line-of-sight averaged electron temperatures less than 1.4 keV at electron densities of (2.5–7.5) × 1013 cm−3. The UTA spectral structure was due to emission from 4d–4f transitions in highly charged ions with average charge states of q = 20–40. A numerical simulation successfully reproduced the observed spectral behavior.

Optical emission spectroscopy of plasma electrolytic oxidation process on 7075 aluminum alloy

Plasma electrolytic oxidation (PEO) on 7075 Al-Zn-Mg-Cu alloy was performed to produce the ceramic coatings in silicate electrolyte at constant voltage. The plasma electron temperature, electron density and atomic ionization degree in plasma zone were evaluated by analyzing the spectral lines of optical emission spectroscopy (OES), and the high spike peaks on plasma temperature profiles were emphatically discussed. The average electron temperature in plasma zone was about 3000K–15,000K, and the electron density was about 4.95×1021m−3–1.65×1022m−3, meanwhile the atomic ionization degree of Al was less than 10−3, while the temperature inside the alloy is below 120°C. It was believed that the high spike peaks on plasma temperature profiles appeared in the later stage of PEO process resulted from the calculation deviation of plasma temperature from weak OES spectral line intensities. The generation of these spike peaks depended on the spark density and illumination intensity rather than the appearance of large discharge sparks, which was different from the previous viewpoint.

Plume Characterization of Electric Solid Propellant Pulsed Microthrusters

Electric solid propellants are an attractive option for propulsion because they are ignited only by an applied electric current. This leads to capabilities such as on-demand throttling and reignition in chemical combustion operation, and it lends itself to application in electric propulsion. In this work, the plasma plume created by electric solid propellant pulsed microthrusters is investigated using a nude Faraday probe, a triple Langmuir probe, and residual gas analysis. The thrusters are tested at a vacuum level of . Results indicate an average plume electron temperature of 1.7 eV and a density of to . A time-of-flight analysis indicates an exhaust velocity of on the centerline. Additionally, ionization fraction is estimated to be 0.3% for an ablation mass bit of on average. Thermal equilibrium and adiabatic expansion calculations suggest a nonequilibrium gas with high-temperature electrons and lower-temperature neutral and ion species. Results indicate the pulsed microthruster operates similar to a coaxial pulsed plasma thruster, which is dominated by electrothermal effects.

Reduction of poloidal magnetic flux consumption during plasma current ramp-up in DEMO relevant plasma regimes

The method for reducing a poloidal magnetic flux consumption of external coils is investigated to reduce the size of the central solenoid (CS) in the DEMO reactor. The reduction of the poloidal magnetic flux consumption during a plasma current ramp-up phase by electron cyclotron (EC) heating is investigated using an integrated modeling code suite, TOPICS. A strongly reversed shear q profile tends to be produced if intense off-axis EC heating is applied to obtain a large reduction of the flux consumption. In order to overcome this tendency, we find a method to obtain the optimum temperature profile which minimizes the poloidal flux consumption for a wide range of the q profile. We try to reproduce the optimum temperature profile for a weakly reversed shear q profile using six EC rays of 20 MW. As a result, the resistive flux consumption during the current ramp-up can be reduced by 63% from the estimation using the Ejima constant of 0.45 and the total flux consumption can be reduced by 20% from the conventional estimation. In addition, we find that the resistive flux consumption is closely related to the volume averaged electron temperature and not to the profile shape. Using this relation, the required heating power is estimated to be 31 MW based on a well established global confinement scaling, ITER L-89P. As a result, it is clarified that the poloidal magnetic flux consumption can be reduced by 20% using 20–31 MW of EC heating for a weakly reversed shear q profile. This reduction of the flux consumption accounts for 10% reduction of the CS radius.

Ion charge state and energy enhancement by axial magnetic field applied during laser produced plasma expansion

AbstractThe effects of axial magnetic field on the properties of the ions ejected from Nd:YAG laser (wavelength = 1064 nm, pulse duration = 6 ns) produced expanding Cu plasma were investigated. A plane Cu target, without and with 0.23 T axial magnetic field at its surface, was irradiated in the fluence range of 2–24 J/cm2. The ions emitted along the target surface normal were analyzed with the help of ion collector and time-of-flight electrostatic ion energy analyzer. The integrated ion yield, highest ion charge state, average ion energy, and energy of individual ion charge states were found to increase by application of the magnetic field. The initial parameters of the non-equilibrium plasma such as average ion charge, equivalent potential, electron temperature, electron density, Debye length, and transient electric field were estimated from the experimental results obtained without and with application of the magnetic field. The increase of ion yield and ion charge state by application of magnetic field are most probably due to the trapping of electrons in front of the target surface, which boosts up the electron impact ionization process. The ion energy increment due to the magnetic field is discussed in the frame work of electrostatic model for ion acceleration in laser plasma.

Spatial and Excitation Variations for Different Applied Voltages in an Atmospheric Neon Plasma Jet**supported by National Natural Science Fundation of China (No. 61271053), the Natural Science Foundation of Jiangsu Province of China (No. BK2012737), the Foundation for Excellent Youth Scholars of Southeast University, China

A neon plasma jet was generated in air, driven by a 9 kHz sinusoidal power supply. The characteristics of the plasma plume and the optical spectra with plasma propagation for different applied voltages were investigated. By increasing the applied voltage, the plasma plume first increases and then retracts to become short and bulky. The shortened effect of Ne plasma plume (about 10 mm) for the further voltage increasing is more apparent than that of He (about 3 mm) and Ar (about 1 mm). Emission intensity of the N2 (337 nm) increases with the applied voltage, gradually substituting the emission intensity of Ne (702 nm and 585 nm) as the noticeable radiation. At the nozzle opening, the Ne (702 nm) emission dominates, while the Ne (585 nm) emission is most noticeable around the tip of the plasma plume. The spatial distribution of the three spectral lines indicates that Ne (702 nm) emission decreases dramatically with plasma propagation while Ne (585 nm) and N2 (337 nm) emissions reach their maxima at the middle of the plasma plume. The results indicate that the Ne (702 nm) emission is much more sensitive to the average electron temperature and the density of the high-energy electrons, so it changes greatly at the tube nozzle and little at the tip region as the voltage increases. The population of high-energy electrons, the average electron temperature, the collision with air molecules and the Penning effect between Ne metastables and air molecules may explain their different variations with plasma propagating and voltage increasing.

Numerical simulation of evolution features of the atmospheric-pressure CF4 plasma generated by the pulsed dielectric barrier discharge

The atmospheric-pressure CF4 plasma has the high application potential in the field of semiconductor fabrication since it can combine the excellent capability for the CF4 plasma etching with the easy atmospheric-pressure operation. In this work, the fluid model has been carried out to numerically research evolution features of the atmospheric-pressure CF4 plasma generated by the pulsed dielectric barrier discharge. The computational results show that the averaged electron temperature dramatically increases during the rising and the falling phases of the applied voltage pulse, and then swiftly decreases. The discharge current density has the waveform of two bipolar short pulses. The electrons and CF3 + ions form the cathode sheath at the discharge duration. However, the CF3 - and F− negative ions take the place of the electrons to sustain the cathode sheath of the CF4 discharge plasma at the time interval between the two bipolar discharge pulses. During the time interval of the two adjacent applied voltage pulses the discharge region is the quasi-neutral plasma region, and meanwhile CF2 + and CF3 - are the dominated charged species. Moreover, F and CF3 maintain the relatively stable high densities and uniform axial distributions during the whole period of the applied voltage.