Effective Electron Temperature Research Articles

Effects of Gas Pressure on the Plasma Properties in a Radial Small Size Inductively Coupled Plasma Reactor

To improve the technology of glow discharge polymer (GDP) thin film deposition and provide theoretical support for the deposition mechanism of GDP thin films, the plasma properties in a special cylinder (radial small size) inductively coupled plasma (ICP) reactor were investigated. High electron energy was observed in this reactor in contrast to radial large reactors. The electron energy relaxation length $\lambda _{\varepsilon } $ in the elastic range was calculated to determine the electron kinetics transition pressure. The electron energy probability functions were found to change from a bi-Maxwellian distribution to a Maxwellian distribution and then into a Druyvesteyn-like distribution. Furthermore, we observed the association ions $\text{Ar}^{+}(+$ Ar) generated by ion-molecule association reactions. In addition, the profiles of plasma parameters, such as the plasma potential $V_{p}$ , the electron density $n_{e}$ , and the effective electron temperature $T_{\mathrm {eff}}$ , were experimentally investigated with increasing gas pressure.

Thermal effects on laser-assisted field evaporation from a Si surface: A real-time first-principles study

This work assessed thermal effects on laser-assisted field evaporation from a Si surface using real-time time-dependent density functional theory calculations. These assessments focused on finite electron and lattice temperatures, both of which were characterized on different time scales. The results show that dangling bonds at clean surfaces assist thermal excitation in response to increased finite electron temperature. It was also determined that thermal excitation induces electron transfer from the surface to the interior of Si in the presence of an electrostatic field, resulting in ionization of the surface atoms. The finite electron temperature effect on evaporation dynamics, however, was found to be negligible. In contrast, increases in the finite lattice temperature evidently induce atomic motion both parallel and perpendicular to the surface, thus appreciably enhancing the evaporation rate in the presence of electrostatic and laser fields. The real-time first-principles simulations “without empirical parameters” presented herein provide theoretical evidence for thermal effects during laser-assisted field evaporation, and this method should also be applicable to various nonequilibrium thermal phenomena, such as laser ablation.

Effect of axial electron temperature and plasma density ramp on self-focusing / defocusing of a laser beam in plasma

In the present study, we analyze the self-focusing / defocusing of an intense laser beam in the plasma under combined effect of density ramp and higher order axial electron temperature. The differential equation for beam width parameter is obtained and then solved numerically under paraxial ray approximation. The behavior of beam width parameter with propagation distance is extensively investigated for different values of optimized parameters and is strongly influenced by the higher order axial electron temperature, Tp4. The results indicate that the electron temperature component Tp4 is not of little significance than Tp0 and Tp2. Under the influence of plasma density ramp and higher order axial electron temperature Tp4 the defocusing is reduced and self-focusing becomes stronger, especially for large propagation distance. Furthermore, increase in the density ramp results more reduction in the laser beam spot size and hence, increase in the intensity of the laser which may be useful for various applications including laser-driven fusion.

Investigation of the power transfer efficiency in a radio-frequency driven negative hydrogen ion source

The radio frequency power transfer efficiency is experimentally and numerically investigated in an inductively coupled negative hydrogen ion source. The discharge is operated in a low pressure range of 0.1–3 Pa at a driving frequency of 2 MHz and an applied power of up to 6 kW. In the experiment, the power transfer efficiency value is determined by measuring the applied power and current through the antenna coil both with and without discharge operation. Fundamental properties, such as electron density and effective electron temperature, are obtained by means of a Langmuir probe. The effect of the antenna coil turns, N, is also studied in a range of 5–9 turns. It is found that more coil turns can significantly enhance the power transfer efficiency due to the remarkably increasing quality factor of the system. Moreover, the experimental results show that the power transfer efficiency first increases and then reaches the maximum with increasing applied power, while it first increases quickly and then rises at a slower rate with increasing gas pressure. In order to give a comprehensive knowledge of the power absorption mechanism, a self-consistent hybrid model is developed. It is found that the numerical results are in reasonable agreement with that measured in the experiment. The numerical results and the analytic solutions in the limit cases of low and high pressures can well explain the various trends of the power transfer efficiency obtained in the experiment. These trends mainly depend on the quality factor Q, the electron density, and the effective electron collision frequency.

Capacitively coupled radio frequency nitrogen plasma generated at two different exciting frequencies of 13.56 MHz and 40 MHz analyzed using Langmuir probe along with optical emission spectroscopy

Capacitively coupled nitrogen plasma discharges driven by two different exciting radio frequencies of 13.56 MHz, and 40 MHz are investigated. Langmuir probe diagnostics along with optical emission spectroscopy are used for interpreting the discharges. The results of these diagnostics are not shown sufficiently in the literature for 40 MHz even though there are some for 13.56 MHz. The electron density ne and the effective electron temperature Teff are calculated from the measurements of the current – voltage characteristics of the discharges. These calculated parameters are correlated with the vibrational temperatures of the N2 second positive system C3Πu−B3Πg and the N2+ first negative system B2Σu+−X2Σg+ measured via optical emission spectroscopy. The population of the vibrational excitation particles plays a crucial role in the determination of the vibrational temperature which strongly depends on ne and Teff. The transition from collisionless stochastic heating mode to collisional Ohmic heating mode into the bulk plasma appears at lower pressure value for 40 MHz as compared to 13.56 MHz. This effect is observed effectively with increasing the RF input power due to the high energy electrons. It is noted that the vibrational temperatures of N2 and N2+ decreases at high-pressure region (>0.3 Torr for 13.56 MHz and >0.2 Torr for 40 MHz) due to a reduction in the relative population of the vibrationally excited particle. The measurements of the Langmuir probe are very consistent with the results of the optical emission spectroscopy.

Interaction of relativistically intense laser pulses with long-scale near critical plasmas for optimization of laser based sources of MeV electrons and gamma-rays

Experiments were performed to study electron acceleration by intense sub-picosecond laser pulses propagating in sub-mm long plasmas of near critical electron density (NCD). Low density foam layers of 300–500 μm thickness were used as targets. In foams, the NCD-plasma was produced by a mechanism of super-sonic ionization when a well-defined separate ns-pulse was sent onto the foam-target forerunning the relativistic main pulse. The application of sub-mm thick low density foam layers provided a substantial increase of the electron acceleration path in a NCD-plasma compared to the case of freely expanding plasmas created in the interaction of the ns-laser pulse with solid foils. The performed experiments on the electron heating by a 100 J, 750 fs short laser pulse of 2–5 × 1019 W cm−2 intensity demonstrated that the effective temperature of supra-thermal electrons increased from 1.5–2 MeV in the case of the relativistic laser interaction with a metallic foil at high laser contrast up to 13 MeV for the laser shots onto the pre-ionized foam. The observed tendency towards a strong increase of the mean electron energy and the number of ultra-relativistic laser-accelerated electrons is reinforced by the results of gamma-yield measurements that showed a 1000-fold increase of the measured doses. The experiment was supported by 3D-PIC and FLUKA simulations, which considered the laser parameters and the geometry of the experimental set-up. Both, measurements and simulations showed a high directionality of the acceleration process, since the strongest increase in the electron energy, charge and corresponding gamma-yield was observed close to the direction of the laser pulse propagation. The charge of super-ponderomotive electrons with energy above 30 MeV reached a very high value of 78 nC.

Effect of Electron Density and Temperature in Oxygen Plasma Treatment of Polystyrene Surface

A plasma treatment of polymeric materials has become one of the most important methods to enhance the surface wettability without affecting the bulk material features. Oxygen plasma treatment of polystyrene surfaces deposited on a QCM sensor was evaluated by relating the plasma parameters, surface roughness, and the wettability. The internal plasma parameters investigated in this work were the electron temperature (Te) and the electron density (ne). The oxygen plasma was generated using an RF power generator. The power was varied by applying a voltage from 60 volts to 100 volts. An Optical Emission Spectroscopy (OES) was used to determine the plasma species, the Te and the ne during the plasma oxygen process. The dominant species in the plasma was excited atomic oxygen or activated oxygen (OI) which was detected from the 774 nm and 842 nm emissions. The higher applied RF voltage resulted in the higher Te and ne. The effect of the Te and ne on the polystyrene surface was observed on the change of the surface roughness. The surface roughness significantly related to the surface wettability observed with a contact angle measurement. Furthermore, the plasma treatment greatly changed the surface from hydrophobic to hydrophilic via reactive processes by the excited atomic oxygen species. This was confirmed by the increase in C = C and C = O functional groups observed using a Fourier transform infrared (FTIR) spectroscopy. The Te and ne may also affected the character of the plasma in terms of its reactivity.

Heating of a degenerate electron ensemble in a well of compound semiconductors at low lattice temperatures

At low lattice temperatures, an ensemble of electrons exhibits some specific features which are hardly observed for higher lattice temperatures. Considering a two-dimensional ensemble of non-equilibrium electrons in a quantum well of compound semiconductors, the dependence of the effective electron temperature upon the electric field has been analysed under the condition when the lattice temperature is low. The aim of the analysis has been to assess how does the degeneracy of the ensemble and the piezoelectric interaction of the electrons, result in changes in the electron temperature characteristics at low lattice temperatures. Numerical results are obtained for quantum wells of InSb, GaAs and GaN which are potentially used for the device purpose. The assessment is made through the comparison of the results obtained from the present analysis with other theoretical and experimental results which are available in the literature. The analysis predicts that the low-temperature features result in significant changes in the characteristics. In the absence of appropriate experimental data in the literature, any conclusive comparison of the theoretical results of the present analysis with the experiment could hardly be made. However, a rather cursory comparison for the wells of GaAs with the indirectly obtained effective temperature characteristics of the electrons shows some qualitative similarity, particularly for the regime of low electric fields. The results of the present approximate analysis being interesting, it holds promise for further work in the same field.

Computational investigation of ion cyclotron heating on Proto-MPEX

Ion cyclotron heating (ICH) on the Prototype Material Plasma Exposure eXperiment (Proto-MPEX) is to be accomplished using the “beach-heating” technique. Beach heating has not been previously demonstrated to efficiently heat core ions at the high electron density values present in Proto-MPEX. This work numerically investigates the wave propagation characteristics of the ICH region on Proto-MPEX to explore avenues for efficient core ion heating. The analysis reveals that finite electron temperature effects are required to predict core ion heating. Cold plasma dispersion analysis and full-wave simulations show that the inertial Alfvén wave (IAW) is restricted from coupling power into the core plasma because (1) the group velocity is too shallow for its energy to penetrate into the core before damping in the periphery and (2) when operating in a magnetic field where ω/ωci≳0.7, the IAW is cut off from the core plasma by the Alfvén resonance. However, including kinetic effects shows that the kinetic Alfvén wave (KAW) can propagate in the electron temperature regime in Proto-MPEX. Full-wave simulations show that when the electron temperature is increased to Te > 2 eV and the edge electron density is sufficiently high needge>1×1017 m−3, ion power absorption in the core increases substantially (≈25% of total power). The increase in ion power absorption in the core is attributed to the propagation of the KAW. Calculations of electron and ion power absorption show that the electron heating is localized around the Alfvén resonance, while the ion heating is localized at the fundamental ion cyclotron resonance.

Statistical study of PMSE response to HF heating in two altitude regions

Polar mesospheric summer echoes (PMSE) often show different layers. Artificial electron heating experiments are an important diagnostic tool to investigate the parameters in the PMSE regions. The response of PMSE to high frequency heating in the lower (80–85 km) and upper (85–90 km) PMSE layers is studied by analyzing PMSE observations carried out by the EISCAT VHF radar in July 2007. Different characteristics of modulated PMSE (e.g., PMSE intensity reduction, recovery, overshoot, ratios during the heating-on and heating-off times) are analyzed and compared at different situations such as only in one layer (lower or upper) and in both layers simultaneously without high-energy particle precipitation. Based on statistical results, it is found that in the lower layer all characteristics of modulated PMSE except PMSE recovery are greater than that in the upper layer. Electron temperature enhancement and PMSE modulation index due to ionospheric heating were calculated to show the enhanced electron temperature effect on PMSE. It is found that in both layers usually higher electron temperature enhancement corresponds to higher PMSE modulation index. However, the comparison of statistical results shows that in the lower layer electron temperature enhancement and PMSE modulation index are greater than that in the upper layer. Based on the relation of electron temperature enhancement to the PMSE modulation index, it is concluded that the variability of electron temperature enhancement may be responsible for the variations in different modulated PMSE characteristics between the lower and upper layers.

Characteristics of a dual‐radio‐frequency cylindrical inductively coupled plasma

The plasma parameters such as electron density, effective electron temperature, plasma potential, and uniformity are investigated in a new dual‐frequency cylindrical inductively coupled plasma (ICP) source operating at two frequencies (2 and 13.56 MHz) and two antennas (a two‐turn high‐frequency antenna and a six‐turn low‐frequency (LF) antenna). It is found that the electron density increases with 2 MHz power, whereas the electron temperature and plasma potential decrease with 2 MHz power at a fixed 13.56 MHz power. Moreover, the plasma uniformity can be improved by adjusting the LF power. These results indicate that a dual‐frequency synergistic discharge in a cylindrical ICP can produce a high‐density, low‐potential, low‐effective‐electron‐temperature, and uniform plasma.

Effects of electron temperature on the ion extraction characteristics in a decaying plasma confined between two parallel plates

In this paper, a one-dimension particle-in-cell (PIC) code (EDIPIC) is employed to simulate the parallel-plate ion extraction process under an externally applied electrostatic field, focusing on the analysis of the influence of the initial electron temperature on the extracted ion fluxes to the metal plates during the ion extraction process. Compared with previously published results, the plasma oscillations on a timescale of the electron plasma period, and the excitation of the ion acoustic rarefaction waves resulting from the plasma oscillations originating from both the negative and positive electrodes, are studied for the first time. The modeling results show that both the negative and positive extractors can collect ions due to the plasma oscillations and the propagation of the ion acoustic rarefaction waves. With the increase of the initial electron temperature achieved by keeping other parameters unchanged, on the one hand, both the ion speed and flux to the negative and positive plates increase, which leads to a significant decrease of the ion extraction time, while on the other hand, the ion flux to the positive plate after the formation of a Child–Langmuir sheath is much more sensitive to an increase of the initial electron temperature than that to the negative plate. The PIC simulation results provide a deeper physical understanding of the influence of the initial electron temperature on the characteristics of the entire ion extraction process in a decaying plasma.

Can we neglect relativistic temperature corrections in thePlanckthermal SZ analysis?

Measurements of the thermal Sunyaev-Zel'dovich (tSZ) effect have long been recognized as a powerful cosmological probe. Here we assess the importance of relativistic temperature corrections to the tSZ signal on the power spectrum analysis of the Planck Compton-$y$ map, developing a novel formalism to account for the associated effects. The amplitude of the tSZ power spectrum is found to be sensitive to the effective electron temperature, $\bar{T}_e$, of the cluster sample. Omitting the corresponding modifications leads to an underestimation of the $yy$-power spectrum amplitude. Relativistic corrections thus add to the error budget of tSZ power spectrum observables such as $\sigma_8$. This could help alleviate the tension between various cosmological probes, with the correction scaling as $\Delta \sigma_8/\sigma_8 \simeq 0.019\,[k\bar{T}_e\,/\,5\,{\rm keV}]$ for Planck. At the current level of precision, this implies a systematic shift by $\simeq 1\sigma$, which can also be interpreted as an overestimation of the hydrostatic mass bias by $\Delta b \simeq 0.046\,(1-b)\,[k\bar{T}_e\,/\,5\,{\rm keV}]$, bringing it into better agreement with hydrodynamical simulations. It is thus time to consider relativistic temperature corrections in the processing of current and future tSZ data.

The Influence of Secondary Electron Emission and Electron Reflection on a Capacitively Coupled Oxygen Discharge

The one-dimensional object-oriented particle-in-cell Monte Carlo collision code oopd1 is applied to explore the role of secondary electron emission and electron reflection on the properties of the capacitively-coupled oxygen discharge. At low pressure (10 mTorr), drift-ambipolar heating of the electrons dominates within the plasma bulk, while at higher pressure (50 mTorr), stochastic electron heating in the sheath region dominates. Electron reflection has negligible influence on the electron energy probability function and only a slight influence on the electron heating profile and electron density. Including ion-induced secondary electron emission in the discharge model introduces a high energy tail to the electron energy probability function, enhances the electron density, lowers the electronegativity, and increases the effective electron temperature in the plasma bulk.

Modeling of argon–acetylene dusty plasma

The properties of an Ar/C2H2 dusty plasma (ion, electron and neutral particle densities, effective electron temperature and dust charge) in glow and afterglow regimes are studied using a volume-averaged model and the results for the glow plasma are compared with mass spectrometry measurements. It is shown that dust particles affect essentially the properties of glow and afterglow plasmas. Due to collection of electrons and ions by dust particles, the effective electron temperature, the densities of argon ions and metastable atoms are larger in the dusty glow plasma comparing with the dust-free case, while the densities of most hydrocarbon ions and acetylene molecules are smaller. Because of a larger density of metastable argon atoms and, as a result, of the enhancement of electron generation in their collisions with acetylene molecules, the electron density in the afterglow dusty plasma can have a peak in its time-dependence. The results of numerical calculations are in a good qualitative agreement with experimental results.

Probing suprathermal electrons by trace rare gases optical emission spectroscopy in low pressure dipolar microwave plasmas excited at the electron cyclotron resonance

In microwave plasmas with the presence of a magnetic field, fast electrons could result from collisionless energy absorption under electron cyclotron resonance (ECR) conditions. In this case, electrons are trapped between the two poles of the magnetic field and rotate at the cyclotron frequency ωce. When crossing a zone where the cyclotron frequency equals the microwave frequency (ωce=ω), electrons see a steady electric field in their reference frame and are constantly accelerated by the right handed polarized (RHP) wave. When the plasma density reaches the so-called critical density nc at which ωpe2=ω2±ωωce, where ωpe is the plasma electron frequency, the left handed polarized (LHP) electromagnetic wave can excite electrostatic waves that can produce collisionless electron heating and fast electron generation by Landau damping. In this study, a combination of the Langmuir probe and trace rare gas optical emission spectroscopy (TRG-OES) is used to analyze the electron energy probability function (EEPF) in microwave (2.45 GHz) low-pressure argon plasmas excited at ECR in a dipolar magnetic field. While both TRG-OES and Langmuir probe measurements agree on the effective electron temperature (TeAll) from 1.6 to 50 mTorr, TRG-OES, which is more sensitive to high energy electrons, shows that the EEPF is the sum of two Maxwellian populations: one described by TeAll and a high energy tail characterized by a temperature TeTail. Spatially resolved-TRG-OES measurements show that the high-energy tail (TeTail) in the EEPF is spatially localized near the magnet, while the effective electron temperature (TeAll) stays constant. The ratio between the high energy tail and the effective temperatures is found to increase with the absorbed microwave power and decrease with increasing pressure. The former phenomenon is ascribed to a rise in ECR heating due to a stronger RHP wave electric field and to an enhanced absorption of the LHP waves. On the other hand, the decrease in the ratio is attributed to a smaller magnetic confinement of the electrons (increase in the collision frequency), which lessens ECR heating and to a decrease in the LHP field intensity at the resonant position, which impedes the conversion into electrostatic waves.

A scanning tunneling microscope for spectroscopic imaging below 90 mK in magnetic fields up to 17.5 T.

We describe the development and performance of an ultra-high vacuum scanning tunneling microscope working under combined extreme conditions of ultra-low temperatures and high magnetic fields. We combined a top-loading dilution refrigerator and a standard bucket dewar with a bottom-loading superconducting magnet to achieve 4.5 days operating time, which is long enough to perform various spectroscopic-imaging measurements. To bring the effective electron temperature closer to the mixing-chamber temperature, we paid particular attention to filtering out radio-frequency noise, as well as enhancing the thermal link between the microscope unit and the mixing chamber. We estimated the lowest effective electron temperature to be below 90 mK by measuring the superconducting-gap spectrum of aluminum. We confirmed the long-term stability of the spectroscopic-imaging measurement by visualizing superconducting vortices in the cuprate superconductor Bi2Sr2CaCu2O8+δ .

Relativistic ponderomotive self-focusing of quadruple Gaussian laser beam in cold quantum plasma

AbstractIn the present paper, we have investigated self-focusing of the quadruple Gaussian laser beam in underdense cold quantum plasma. The non-linearity chosen is associated with the relativistic mass effect that arises due to quiver motion of electron and electron density perturbation caused by ponderomotive force. The non-linearity modifies the plasma frequency in the dielectric function and hence the refractive index of the medium. The focusing/defocusing of the quadruple laser depends on the refractive index of the medium. We have set up non-linear differential equation that controls the beam width parameter by using well-known paraxial ray approximation and Wentzel–Krammers–Brillouin approximation. The effect of intensity parameter and electron temperature is observed on laser beam self-focusing in the presence of cold quantum plasma. From the results, it is revealed that electron temperature and the initial intensity of the laser beam control the profile dynamics of the laser beam.

Self-focusing and defocusing of cosh Gaussian laser beam in the presence of nonlinearity of ponderomotive force and temperature gradient

In this paper, the propagation of Cosh Gaussian laser beam and its interaction with isothermal plasma without temperature gradient as well as the effect of the exponential electron temperature gradient are investigated. Here the ponderomotive nonlinearity force is effective mechanism. This force can modify the electron density distribution. All the investigations are carried out for different initial plasma temperatures. Using Maxwell’s equations we obtained the nonlinear second-order differential equation of the dimensionless beam-width parameter (f) on the distance of propagation for several initial electron temperatures and exponential temperature variations. These equations are solved numerically by taking WKB and paraxial approximation. Under the effect of initial electron temperature, self-focusing and defocusing of hyperbolic cosine (cosh) Gaussian laser beam is distinguished. Furthermore, the exponential temperature gradient cause to stationary propagation mode breaks, and self-focusing or defocusing properties is observable.

Investigation of the temperature dependent field emission from individual ZnO nanowires for evidence of field-induced hot electrons emission

ZnO nanowires as field emitters have important applications in flat panel display and x-ray source. Understanding the intrinsic field emission mechanism is crucial for further improving the performance of ZnO nanowire field emitters. In this article, the temperature dependent field emission from individual ZnO nanowires was investigated by an in situ measurement in ultra-high vacuum. The divergent temperature-dependent Fowler–Nordheim plots is found in the low field region. A field-induced hot electrons emission model, that takes into account penetration length, is proposed to explain the results. The carrier density and temperature dependence of the field-induced hot electrons emission current are derived theoretically. The obtained results are consistent with the experimental results, which could be attributed to the variation of effective electron temperature. All of these are important for a better understanding on the field emission process of semiconductor nanostructures.