Decrease In Electron Temperature Research Articles

Determination of the Electron Temperature of Atmospheric Pressure Argon Plasmas by Absolute Line Intensities and a Collisional Radiative Model

The electron temperature in atmospheric argon plasmas created by a DBD jet is determined using a combination of Absolute Line Intensity (ALI) measurements and a collisional radiative model (CRM). The ALI measurements have been performed to determine the densities of the states in the 4p level. In addition, the ground state density is taken into account, which is found via the pressure and the gas temperature. The density ratio of the ground state and 4p state gives a value of the excitation temperature, which by means of the CRM is transformed into the electron temperature. With this method, the electron temperature in the active zone of a pure argon plasma is found to be 1.27 eV which is significantly higher than the experimental value reported by others. An error analysis shows that the relative error in the electron temperature obtained in this way is about 5%. In the afterglow, the temperature decreases gradually to about 0.88 eV. The addition of 2% O2 leads to a decrease in electron temperature of about 5%.

Simulation of Radiation Cooling Effects in the GAMMA 10 West End‐Cell Using Fluid Model

AbstractWe have started a simulation study of background plasma in the GAMMA 10 west end‐cell using fluid‐code in order to understand divertor simulation experiment. This fluid code is B2 code without including the effects of drifts and currents. In this paper, we obtained the effects of additional neutral particles density. As increasing amount of additional neutral particle density, ion and electron temperature decrease and plasma density builds up. Especially, the peak of plasma density moves from z = 10.04 m from z = 10.1 m. However, electron temperature does not decrease detachment front for high ion temperature. Therefore, it needs that ion temperature is decreased. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Theoretical Study on the Characteristics of Atmospheric Radio Frequency Discharges by Altering Electrode Gap

In this paper, we present a theoretical study on the discharge characteristics of radio-frequency discharges at atmospheric pressure driven by a higher frequency of 40.68 MHz while the electrode gap is altered. Based on the analytical equations and simulation data from a one-dimensional fluid model, an optimal gap between electrodes, at which the largest electron density is obtained, can be observed under a constant power condition; however, as the electrode gap increases the time-averaged electron temperature decreases, and the underpinning physics is also discussed based on the simulation results. This study indicates that at a constant power by choosing an appropriate electrode spacing, the rf discharge can be effectively optimized at atmospheric pressure.

Study on the Plume Characteristics of Pulsed Plasma Thruster

A current-model Triple Langmuir probe was developed and used to measure electron temperature and density of the Pulsed Plasma Thruster plume. To decreasing the errors in measurement, Probe, collection circuit and glow cleaning devices were elaborately designed. A FIR digital Filter based on Matlab was designed and the software for date processing was developed by Labview. Measurements were taken at various position in the plume of a Pulsed Plasma Thruster operating at discharge energy of 6-24J. The results show the thruster plume has electron temperatures in the range between 0.6and 5.4eV, electron densities between 0.9×1019 and 4.1x1021m-3 for all discharge energy levels considered. Electron temperature and density decrease with increasing angle away from the centerline and with decreasing discharge energy.

Characteristics of SiO2 etching by using pulse-time modulation in 60 MHz/2 MHz dual-frequency capacitive coupled plasma

60 MHz pulsed radio frequency (rf) source power and 2 MHz continuous wave rf bias power, were used for SiO2 etching masked with an amorphous carbon layer (ACL) in an Ar/C4F8/O2 gas mixture, and the effects of the frequency and duty ratio of the 60 MHz pulse rf power on the SiO2 etch characteristics were investigated. With decreasing duty ratio of the 60 MHz pulse rf power, not only the etch rate of SiO2 but also the etch rate of ACL was decreased, however, the etch selectivity of SiO2 over ACL was improved with decreasing the duty ratio. On the other hand, when the pulse frequency was varied at a constant duty ratio, no significant change in the etch rate and etch selectivity of both materials could be observed. The variation of the etch characteristics was believed to be related to the change in the gas dissociation characteristics caused by the change in the average electron temperature for different pulsing conditions. The improvement in the etch selectivity with the decrease of duty ratio, therefore, was related to the decreased gas dissociation of C4F8 by the decrease of average electron temperature and, which resulted in a change in composition of the fluorocarbon polymer on the etched materials surface from C–C rich to CF2 rich. With decreasing the duty ratio, not only the etch selectivity but also the improvement in the SiO2 etch profile could be observed.

Electron Temperature and Density Measurements by Using Thomson Scattering System in GAMMA 10

Thomson scattering (TS) is the most reliable diagnostic to measure the electron temperature and electron density radial profiles. In GAMMA 10, the yttrium-aluminium-garnet (YAG)-TS system was constructed with the large solid angle of TS collection optics. We carried out the Rayleigh and Raman scattering experiments for system settings and applied the YAG-TS system to the GAMMA 10 plasma. We can successfully measure the electron temperature and density radial profiles in the central cell of GAMMA 10 by using YAG-TS system. The supersonic molecular beam injection (SMBI) experiments have been started for plasma fueling study in GAMMA 10. In SMBI experiments, we observed the electron temperature decrease and electron density increase in the plasma center.

Plasma parameters and electron energy distribution functions in a magnetically focused plasma

Spatially resolved measurements of ion density, electron temperature, floating potential, and the electron energy distribution function (EEDF) are presented for a magnetically focused plasma. The measurements identify a central plasma column displaying Maxwellian EEDFs at an electron temperature of about 5 eV indicating the presence of a significant fraction of electrons in the inelastic energy range (energies above 15 eV). It is observed that the EEDF remains Maxwellian along the axis of the discharge with an increase in density, at constant electron temperature, observed in the region of highest magnetic field strength. Both electron density and temperature decrease at the plasma radial edge. Electron temperature isotherms measured in the downstream region are found to coincide with the magnetic field lines.

High-latitude ionospheric response to the solar eclipse of 1 August 2008: EISCAT observations and TRANSCAR simulation

On 1 August 2008, a total solar eclipse occurred and the footprint of its umbra passed North–East of the Svalbard archipelago, where the EISCAT Svalbard Radars (ESR) are installed. This eclipse is peculiar because it was seen at high-latitude, thus with large solar zenith angles and it was the first time that incoherent scatter radars were able to sound the ionospheric response at such a high latitude. The ESR data, after correction, show the typical signatures of a solar eclipse: depletion in electron density in the E- and F-regions, a decrease in electron temperature in the F-region, and a downflow of ions. Also, the UHF dish of the mainland EISCAT system measured a decrease in the same parameters, showing the influence of the penumbra (partial eclipse) on the ionosphere. We have modelled the response of the high-latitude ionosphere to this solar eclipse with the TRANSCAR code. Our simulations reproduce rather well the observations above the UHF radar in Tromsø and the ESR on Svalbard. In particular, we show the influence of particle precipitation above the ESR and we suspect an effect above Tromsø of the photoelectrons coming from the opposite hemisphere. Another interesting and quite unusual feature is the observation of the summer ionospheric cusp undergoing the eclipse. Radar data show structures of enhanced electron temperature, due to soft particle precipitation through the polar cusp.

Time-gated measurements of electron beam generated Kα emission lines from brass planar wire array implosions

The relative amount of Kα radiation emitted by partially ionized copper and zinc from planar wire arrays on the 1 MA Zebra generator at the University of Nevada, Reno, does not correspond to the composition (70% copper, 30% zinc) of the array's brass wires. For example, the copper Kα line at 8 keV was observed to be much stronger than would be expected from zinc's Kα radiation at 8.6 keV, but this ratio also reversed, more emission from zinc than from copper, during the X-ray pulse. An excess of Kα photons from copper is consistent with a beam of electrons with energies above copper's K-edge but below that of zinc, but the opposite case is perplexing. Preferential ablation of Zn over Cu early in the current pulse could be a contributing factor, but opacity effects are not. Synthetic spectra for brass computed by a non-LTE collisional-radiative model that includes an electron beam component compare well with observed K-shell spectra, and suggest the parent ions of the Kα emission. These ionization stages are consistent with L-shell spectra. This comparison also indicates that the total energy in the electron beam increases towards the end of the radiation pulse while the electron temperature decreases. The crucial diagnostic in this measurement is a time-resolved X-ray spectrometer based on a LiF crystal.

Ionospheric anomalies associated with the Haiti earthquake of 12 January 2010 observed by DEMETER satellite

Abstract. This paper examines the ionospheric anomalies around the time of a strong earthquake (M = 7.0) which occurred in Haiti region (18.457° N, 72.533° W) on 12 January 2010. DEMETER satellite data have been used to study the plasma parameters variation during the Haiti earthquake. One day (11 January 2010) before the earthquake there is a significant enhancement of electron density and electron temperature near the epicenter. Decrease of electron temperature is observed few days after the earthquake. Anomalous plasma parameter variations are detected both in day and nighttimes before the quake. Statistical processing of the DEMETER data demonstrates that satellite data can play an important role for the study of precursory phenomena associated with earthquakes.

Quantitative analysis of diamond deposition reactor efficiency

Optical emission spectroscopy has been used to characterize diamond deposition microwave chemical vapour deposition (MWCVD) plasmas operating at high power density. Electron temperature has been deduced from H atom emission lines while H-atom mole fraction variations have been estimated using actinometry technique, for a wide range of working conditions: pressure 25–400hPa and MW power 600–4000W. An increase of the pressure from 14hPa to 400hPa with a simultaneous increase in power causes an electron temperature decrease from 17,000K to 10,000K and a H atom mole fraction increase from 0.1 to up to 0.6. This last value however must be considered as an upper estimate due to some assumptions made as well as experimental uncertainties.

Energy relaxations of hot electrons in AlGaN/AlN/GaN heterostructures grown by MOCVD on sapphire and 6H-SiC substrates

In this work, we investigated the hot-electron dynamics of AlGaN/GaN HEMT structures grown by MOCVD on sapphire and SiC substrates at 80 K. High-speed current-voltage measurements and Hall measurements over the temperature range 27–300 K were used to study hot-electron dynamics. At low fields, drift velocity increases linearly, but deviates from the linearity toward high electric fields. Drift velocities are deduced as approximately 6.55 × 10 6 and 6.60 × 10 6 cm/s at an electric field of around E ~ 25 kV/cm for samples grown on sapphire and SiC, respectively. To obtain the electron temperature as a function of the applied electric field and power loss as a function of the electron temperature, we used the so-called mobility comparison method with power balance equations. Although their low field carrier transport properties are similar as observed from Hall measurements, hot carrier energy dissipation differs for samples grown on sapphire and SiC substrates. We found that LO-phonon lifetimes are 0.50 ps and 0.32 ps for sapphire and SiC substrates, respectively. A long hot-phonon lifetime results in large non- equilibrium hot phonons. Non-equilibrium hot phonons slow energy relaxation and increase the momentum relaxation. The effective energy relaxation times at high fields are 24 and 65 ps for samples grown on sapphire and SiC substrates, respectively. They increase as the electron temperature decreases.

Control of ion energy distributions using a pulsed plasma with synchronous bias on a boundary electrode

Ion energy distributions (IEDs) on a grounded substrate in a Faraday-shielded argon inductively coupled plasma were measured with a retarding field energy analyzer. A Langmuir probe was also used to measure space- and time-resolved plasma parameters. IEDs and plasma parameters were studied with continuous or pulsed positive dc bias voltage on a ‘boundary electrode’ in contact with the plasma. For continuous wave plasmas without applied bias, the IED exhibited a single broad peak at the plasma potential. Applying a continuous positive dc bias on the boundary electrode shifted the peak of the IED to higher energy. Application of a synchronous dc bias on the boundary electrode during the afterglow of a pulsed plasma resulted in a double-peaked IED. The mean energies of the two peaks, as well as the peak separation, were controlled by adjusting the applied dc bias and the discharge pressure. The full width at half maximum (FWHM) of the peak corresponding to the synchronous dc bias diminished with decreasing electron temperature. The FWHM was controlled by varying the time window in the afterglow during which dc bias was applied.

DEGENERACY EFFECT ON THE COMPTON SCATTERING POWER

The Compton scattering is one of the loss processes in fusion media. In this paper the Compton cross-section is calculated in three limits of temperature, non-relativistic, relativistic and ultra-relativistic temperatures. By considering the electron distribution function for all the temperature limits, we found the power of Compton scattering in degenerate media. These results show that the Compton scattering power increases with decreasing electron temperature. So, in degenerate conditions, the Compton loss processes decrease in fusion media.

Ar流速对多级弧放电装置中Ar等离子特性的影响

In this study PLASIMO program developed by Eindhoven University of Technology was used to investigate the effects of argon flow velocity on argon plasma in the cascaded arc. The simulation results are in good agreement with available experimental data that along the symmetry axis, the pressure decreases but the electron temperature increases from the inlet to the outlet. The effects of flow velocity of argon on plasma properties were investigated. The simulation results show that for argon arc discharges, with increasing the flow velocity, the electron density and the heavy particle temperature increases, while the electron temperature decreases. Along the symmetry axis, the electron temperatures are all above 1 eV and the heavy particle temperatures are all about 1 eV at differe

Determination of electron density and temperature in a capacitively coupled RF discharge in neon by OES complemented with a CR model

A method of determination of electron temperature and electron density in plasmas based on optical emission spectroscopy complemented with collisional–radiative modelling (OES/CRM) was studied in this work. A radiofrequency (13.56 MHz) capacitively coupled discharge in neon at 10 Pa was investigated by intensity calibrated optical emission spectroscopy. The absolute intensities of neon transitions between 3p and 3s states were fitted with a collisional–radiative (CR) model in order to determine the electron temperature and electron density. Measuring techniques such as imaging with an ICCD camera were adopted for supplementary diagnostics. The obtained results were compared with the results of compensated Langmuir probe measurement and one-dimensional particle-in-cell/Monte Carlo (PIC/MC) simulation.The results of OES/CRM and PIC/MC method were in close agreement in the case of electron temperature in the vicinity of a driven electrode. The determined value of electron temperature was about 8 eV. In bulk plasma, the measured spectra were not satisfactorily fitted. In the case of electron density only relative agreement was obtained between OES/CRM and Langmuir probe measurement; the absolute values differed by a factor of 5. The axial dependence of electron density calculated by PIC/MC was distinct from them, reaching the maximum values between the results of the other two methods. The investigation of power dependence of plasma parameters close to the driven electrode showed a decrease in electron temperature and an increase in electron density together with increasing incoming RF power. The calculated spectra fitted very well the measured spectra in this discharge region.

Conditions for establishing quasistable double layers in the Earth’s auroral upward current region

The strength and stability of simulated double layers at the ionosphere-auroral cavity boundary have been studied as a function of cold ionospheric electron temperature and density. The simulations are performed with an open boundary one-dimensional particle-in- cell (PIC) simulation and are initialized by imposing a density cavity within the simulation domain. The PIC simulation includes H+ and O+ ion beams, a hot H+ background population, cold ionospheric electrons, and a hot electron population. It is shown that a double layer remains quasistable for a variety of initial conditions and plasma parameters. The average potential drop of the double layer is found to increase as the cold electron temperature decreases. However, in terms of cold electron density, the average potential drop of the double layer is found to increase up to some critical cold electron density and decreases above this value. Comparisons with FAST observations are made and agreement is found between simulation results and observations in the shape and width of the double layer. This study helps put a constraint on the plasma conditions in which a DL can be expected to form and remain quasistable.

Effects of Supersonic Molecular Beam Injection (SMBI) on Plasma Performance in Heliotron J

AbstractGas fueling by supersonic molecular beam injection (SMBI) is successfully applied to ECH/NBI plasmas in Heliotron J. The stored energy reached ∼4.5 kJ for a heating combination of ECH (∼0.35 MW) and NBI (∼0.6 MW), which is about 50 % higher than the maximum one achieved so far under the conventional gas‐puffing in Heliotron J. After an SMBI pulse for ECH+NBI plasma, two different kinds of perturbation in the radiation profile are caused simultaneously in the center and the peripheral regions. For ECH plasma, an SMBI pulse causes increase or decrease of electron temperature, which seems to depend on the target density (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermal analysis of femtosecond laser processing for metal thin films

The temperature distributions in a metal film heated by femtosecond lasers are investigated in this paper. The time scale in which energy transfers from the electrons to the lattice is of the order of a picosecond for metals. Therefore, when the duration of femtosecond laser heating of metal films is of the order of or shorter than a picosecond, substantial nonequilibrium can occur between the electron and lattice temperatures and the metal lattices stay almost thermally undisturbed in this highly nonequilibrium regime. Assuming the system to be one dimensional and insulated at the front and rear surfaces, a parabolic two-temperature model is employed to investigate temperature distributions in metal films irradiated by a femtosecond laser. Using the Laplace transformation technique and the iterative method to solve the nonlinear model, the results reveal that the electron temperature distribution along x decreases with increasing absorption depth, coupling factor and electron specific heat. The high thermal conductivity leads to a decrease in electron temperature with time near the front surface of the film but an increase in electron temperature with time near the rear surface of the film.

Fluid simulation for influence of metastable atoms on the characteristics of capacitively coupled argon plasmas

One-dimensional self-consistent fluid model is used to simulate the capacitively coupled argon plasma, in which the metastable effect on the plasma parameters at different discharge conditions is investigated. The results show that due to the metastable atom existence, the bulk plasma density drops significantly, especially at high pressures, high voltages, and high frequencies, accompanied by the decrease in electron temperature in the bulk. When the pressure and voltage are high, the metastable atom density is characterized by a saddle distribution in the axis direction. However, with the decrease in voltage and pressure, the metastable atom density becomes a parabolic distribution. Besides, the curve of plasma density with frequency has a minimum, and so is the profile of metastable atom density.