Decrease In Electron Temperature Research Articles

The Radial Distribution of Ions and Electrons in RF Inductively Coupled H2/T2B Plasmas

A glow discharge polymer (GDP) was fabricated using trans-2-butene (T2B) and hydrogen (H2) via a plasma-enhanced chemical vapor deposition (PECVD) system. The uniformity of the GDP films was significantly affected by the radial distribution of the H2/T2B plasma parameters. The plasma properties while discharging by a multi-carbon gas source of mixed H2/T2B were investigated during the GDP deposition process. The main positive ions and ion energy distributions in inductively coupled H2/T2B plasmas were analyzed by energy-resolved mass spectrometer (MS), and the electron density and the effective electron temperature were mainly analyzed using a Langmuir probe. The MS results show that the main positive ions in the plasmas are \({\text{C}}_{ 2} {\text{H}}_{ 4}^{ + }\), \({\text{C}}_{ 2} {\text{H}}_{ 6}^{ + }\), \({\text{C}}_{ 3} {\text{H}}_{ 3}^{ + }\), \({\text{C}}_{ 3} {\text{H}}_{ 6}^{ + }\), \({\text{C}}_{ 3} {\text{H}}_{ 8}^{ + }\), \({\text{C}}_{ 4} {\text{H}}_{ 5}^{ + }\), \({\text{C}}_{ 4} {\text{H}}_{ 1 0}^{ + }\), \({\text{C}}_{ 5} {\text{H}}_{ 5}^{ + }\), and \({\text{C}}_{ 5} {\text{H}}_{ 7}^{ + }\) with mass-to-charge ratios (m/e) of 28, 30, 39, 42, 44, 53, 58, 65, and 67, respectively. For a normalized ion intensity, the relative intensities of saturated CH ions increase with increasing radial distance, while the unsaturated CH ions decrease with increasing radial distance. The ion energy distribution of \({\text{C}}_{ 2} {\text{H}}_{ 6}^{ + }\) (m/e = 30) presents a bimodal structure. Additionally, both the electron density and the effective electron temperature decrease with increasing radial distance.

Effects of gas pressure on plasma characteristics in dual frequency argon capacitive glow discharges at low pressure by a self-consistent fluid model**Project supported by the National Natural Science Foundation of China (Grant No. 51172101).

A self-consistent fluid model for dual radio frequency argon capacitive glow discharges at low pressure is established. Numerical results are obtained by using a finite difference method to solve the model numerically, and the results are analyzed to study the effect of gas pressure on the plasma characteristics. It shows that when the gas pressure increases from 0.3 Torr (1 Torr = 1.33322×102 Pa) to 1.5 Torr, the cycle-averaged plasma density and the ionization rate increase; the cycle-averaged ion current densities and ion energy densities on the electrodes electrode increase; the cycle-averaged electron temperature decreases. Also, the instantaneous electron density in the powered sheath region is presented and discussed. The cycle-averaged electric field has a complex behavior with the increasing of gas pressure, and its changes take place mainly in the two sheath regions. The cycle-averaged electron pressure heating, electron ohmic heating, electron heating, and electron energy loss are all influenced by the gas pressure. Two peaks of the electron heating appear in the sheath regions and the two peaks become larger and move to electrodes as the gas pressure increases.

Electron kinetics in capacitively coupled plasmas modulated by electron injection

The controlling effect of an electron injection on the electron energy distribution function (EEDF) and on the energetic electron flux, in a capacitive radio-frequency argon plasma, is studied using a one-dimensional particle-in-cell/Monte Carlo collisions model. The input power of the electron beam is as small as several tens of Watts with laboratory achievable emission currents and energies. With the electron injection, the electron temperature decreases but with a significant high energy tail. The electron density, electron temperature in the sheath, and electron heating rate increase with the increasing emission energy. This is attributed to the extra heating of the energetic electrons in the EEDF tail. The non-equilibrium EEDF is obtained for strong non-local distributions of the electric field, electron heating rate, excitation, and ionization rate, indicating the discharge has transited from a volume heating (α-mode dominated) into a sheath heating (γ-mode dominated) type. In addition, the electron injection not only modifies the self-bias voltage, but also enhances the electron flux that can reach the electrodes. Moreover, the relative population of energetic electrons significantly increases with the electron injection compared to that without the electron injection, relevant for modifying the gas and surface chemistry reactions.

SAMI3 prediction of the impact of the 21 August 2017 total solar eclipse on the ionosphere/plasmasphere system

AbstractWe present quantitative predictions of the impact of the upcoming total solar eclipse on the ionosphere and plasmasphere using the Naval Research Laboratory (NRL) model Sami3 is Also a Model of the Ionosphere (SAMI3). The eclipse will occur over the continental United States on 21 August 2017. Our simulation results indicate that in the vicinity of the eclipse (1) the total electron content (TEC) decreases by up to ∼ 5 TEC units (TECU; 1 TECU = ×1016 m−2) which is a ∼ 35% decrease in TEC, (2) the electron density decreases by a factor of ∼ 50% in the F region, (3) the electron temperature decreases by up to ∼800 K in the plasmasphere, and (4) the O+ velocity changes from ∼40 m s−1 upward to ∼20 m s−1 downward in the F region. Interestingly, the continental size modification of the ionospheric conductance modifies the global electric field, which should lead to measurable changes in the TEC in the southern conjugate hemisphere ( 1 TECU).

Cold and warm electrons at comet 67P/Churyumov-Gerasimenko

Strong electron cooling on the neutral gas in cometary comae has been predicted for a long time, but actual measurements of low electron temperature are scarce. We present in situ measurements of plasma density, electron temperature and spacecraft potential by the Rosetta Langmuir probe instrument, LAP. Data acquired within a few hundred km from the nucleus are dominated by a warm component with electron temperature typically 5--10 eV at all heliocentric distances covered (1.25 to 3.83 AU). A cold component, with temperature no higher than about 0.1 eV, appears in the data as short (few to few tens of seconds) pulses of high probe current, indicating local enhancement of plasma density as well as a decrease in electron temperature. These pulses first appeared around 3 AU and were seen for longer periods close to perihelion. The general pattern of pulse appearance follows that of neutral gas and plasma density. We have not identified any periods with only cold electrons present. The electron flux to Rosetta was always dominated by higher energies, driving the spacecraft potential to order -10 V. The warm (5--10 eV) electron population is interpreted as electrons retaining the energy they obtained when released in the ionisation process. The sometimes observed cold populations with electron temperatures below 0.1 eV verify collisional cooling in the coma. The cold electrons were only observed together with the warm population. The general appearance of the cold population appears to be consistent with a Haser-like model, implicitly supporting also the coupling of ions to the neutral gas. The expanding cold plasma is unstable, forming filaments that we observe as pulses.

Observation and particle simulation of vaporized W, Mo, and Be in PISCES-B plasma for vapor-shielding studies

Interactions of Tungsten (W), Molybdenum (Mo), and Beryllium (Be) vapors with a steady-state plasma were studied by the PISCES-B liner plasma experiments as well as Particle-In-Cell (PIC) simulations for the understanding of vapor-shielding phenomena. Effective cooling of the plasma by laser-generated Be vapor was observed in PISCES-B. On the other hand, no apparent cooling was observed for W and Mo vapors. The PIC simulation explains these experimental observations of the difference between low-Z and high-Z vapors. Decrease of electron temperature due to the vapor ejection was observed in case of a simulation of the Be vapor. As for the W vapor, it was found that the plasma cooling is localized only near the wall at a higher electron density plasma (∼1019m−3). On the other hand, the appreciable plasma cooling can be observed in a lower density plasma (∼1018m−3) for the W vapor.

RF plasma generation in the chamber with the conducting walls

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

Time-resolved electron density and electron temperature measurements in nanosecond pulse discharges in helium

Thomson scattering is used to study temporal evolution of electron density and electron temperature in nanosecond pulse discharges in helium sustained in two different configurations, (i) diffuse filament discharge between two spherical electrodes, and (ii) surface discharge over plane quartz surface. In the diffuse filament discharge, the experimental results are compared with the predictions of a 2D plasma fluid model. Electron densities are put on an absolute scale using pure rotational Raman spectra in nitrogen, taken without the plasma, for calibration. In the diffuse filament discharge, electron density and electron temperature increase rapidly after breakdown, peaking at ne ≈ 3.5 · 1015 cm−3 and Te ≈ 4.0 eV. After the primary discharge pulse, both electron density and electron temperature decrease (to ne ~ 1014 cm−3 over ~1 µs and to Te ~ 0.5 eV over ~200 ns), with a brief transient rise produced by the secondary discharge pulse. At the present conditions, the dominant recombination mechanism is dissociative recombination of electrons with molecular ions, . In the afterglow, the electron temperature does not relax to gas temperature, due to superelastic collisions. Electron energy distribution functions (EEDFs) inferred from the Thomson scattering spectra are nearly Maxwellian, which is expected at high ionization fractions, when the shape of EEDF is controlled primarily by electron–electron collisions. The kinetic model predictions agree well with the temporal trends detected in the experiment, although peak electron temperature and electron density are overpredicted. Heavy species temperature predicted during the discharge and the early afterglow remains low and does not exceed T = 400 K, due to relatively slow quenching of metastable He* atoms in two-body and three-body processes. In the surface discharge, peak electron density and electron temperature are ne ≈ 3 · 1014 cm3 and Te ≈ 4.25 eV, attained after the surface ionization wave reaches the grounded electrode. The sensitivity of the present diagnostics is too low to measure electron density in the plasma during surface ionization wave propagation (estimated to be below ne ≈ 1013 cm−3). After peaking during the primary current pulse, the electron density decays due to dissociative recombination. Electron temperature decreases rapidly over ~150 ns after the primary current pulse rise, to Te ≈ 0.5 eV, followed by a much more gradual electron cooling between the primary and the secondary discharge pulses, due to superelastic collisions providing moderate electron heating in the afterglow.

Preliminary Study of a Hybrid Helicon-ECR Plasma Source

A new type of hybrid discharge is experimentally investigated in this work. A helicon source and an electron cyclotron resonance (ECR) source were combined to produce plasma. As a preliminary study of this type of plasma, the optical emission spectroscopy (OES) method was used to obtain values of electron temperature and density under a series of typical conditions. Generally, it was observed that the electron temperature decreases and the electron density increases as the pressure increased. When increasing the applied power at a certain pressure, the average electron density at certain positions in the discharge does not increase significantly possibly due to the high degree of neutral depletion. Electron temperature increased with power in the hybrid mode. Possible mechanisms of these preliminary observations are discussed.

Supersonic molecular beam injection effects on tokamak plasma applied non-axisymmetric magnetic perturbation

The change of tokamak plasma behavior by supersonic molecular beam injection (SMBI) was investigated by applying a three-dimensional magnetic perturbation that could suppress edge localized modes (ELMs). From the time trace of decreasing electron temperature and with increasing plasma density keeping the total confined energy constant, the SMBI seems to act as a cold pulse on the plasma. However, the ELM behaviors were changed drastically (i.e., the symptom of ELM suppression has disappeared). The plasma collisionality in the edge-pedestal region could play a role in the change of the ELM behaviors.

Effect of collisional temperature isotropisation on ELM parallel transport in a tokamak scrape-off layer

We develop a hybrid model to describe the parallel transport in a tokamak scrape-off layer following an edge-localized mode (ELM) event. The parallel dynamics is treated with a kinetic Vlasov–Poisson model, while the evolution of the perpendicular temperature is governed by a fluid equation. The coupling is ensured by isotropising collisions. The model generalises an earlier approach where was constant in space and time (Manfredi et al 2011 Plasma Phys. Control. Fusion 53 015012). Numerical results show that the main effect comes from electron–electron collisions, which limit the decrease of the parallel electron temperature and increase the potential drop in the Debye sheath in front of the surface. Ion–ion collisions have an almost negligible impact. The net effect is an increased peak power load on the target plates.

SIMULATION OF IONOSPHERIC HEATING BASED ON SAMI2 MODEL

AbstractWith artificial heating term (Qhf) added in the electron energy equation of SAMI2 model, the disturbance amplitude of electron temperature and density along field line is simulated. The effects of disturbances under different heating conditions are also compared. The results show that the terrestrial ionospheric plasma can be heated by powerful high‐frequency radio waves, which can result in the rising of the temperature of electron in the whole field line, especially at the heated spot where electron temperature enhances more than 3 times; the pressure balance is broken as the increase in the electron temperature, which leads to plasma diffusion and then perturbation of electron density occurred; electron density gradient perpendicular to magnetic field line changes in accordance with the perturbation of electron density; the perturbation amplitude of electron temperature and density decreases during the heating time, which gradually becomes saturated. Electron temperature and density have a nonlinear relationship with the intensity of heating source.

Low-pressure hydrogen plasmas explored using a global model

Low-pressure hydrogen plasmas have found applications in a variety of technology areas including fusion, neutral beam injection and material processing applications. To better understand these discharges, a global model is developed to predict the behaviour of electrons, ground-state atomic and molecular hydrogen, three positive ion species (H+, , and ), a single negative ion species (H−), and fourteen vibrationally excited states of molecular hydrogen (–14)). The model is validated by comparison with experimental results from a planar inductively coupled GEC reference cell and subsequently applied to the MAGPIE linear helicon reactor.The MAGPIE reactor is investigated for a range of pressures from 1 to 100 mTorr and powers up to 5 kW. With increasing power between 50 W and 5 kW at 10 mTorr the density of all charged species increases as well as the dissociative fraction while the electron temperature remains almost constant at around 3 eV. For gas pressures from 1–100 mTorr at an input power of 1 kW, the electron density remains almost constant, the electron temperature and dissociative fraction decreases, while density increases in density and also dominates amongst ion species. Across these power and pressure scans, electronegativity remains approximately constant at around 2.5%. The power and pressure determines the dominant ion species in the plasma with observed to dominate at high pressures and low powers whereas H+ tends to be dominant at low pressures and high powers.A sensitivity analysis is used to demonstrate how experimental parameters (power, pressure, reactor wall material, geometry etc) influence individual species’ density as well as the electron temperature. Physical reactor changes including the length, radius and wall recombination coefficient are found to have the largest influence on outputs obtained from the model.

Three distinct modes in a surface micro-discharge in atmospheric pressure He + N2 mixtures

A surface micro-discharge in atmospheric pressure He + N2 mixtures is studied in this paper with an emphasis on the discharge modes. With the N2 admixture increasing from 0.1% to 20%, the discharge evolves from a spatially diffuse mode to a filamentary mode during positive half-cycles of the applied voltage. However during the negative half-cycles, an additional patterned mode emerges between the diffuse and the filamentary modes, which has not been reported before to exist in surface micro-discharges. In the diffuse and patterned modes, the plasmas cover almost the entirety of the mesh area during one cycle after plasma ignition in all mesh elements, and the discharge power increases linearly with the applied voltage. In contrast, plasma coverage of the mesh area is only partial in the filamentary mode and the plasma is more unstable with the discharge power increasing exponentially with the applied voltage. As the surface micro-discharge evolves through the three modes, the density of excited species changes significantly, for instance, the density of N2+(B) drops by ∼20-fold from [N2] = 0.2% to 20%. The N2+(B) is predicted to be generated mainly through successive processes of Penning ionization by helium metastables and electron-impact excitation of N2+(X), the latter is most responsible for the density decrease of N2+(B) because much more N2+(X) is converted to N4+(X) as the increase of N2 fraction. Also, the electron density and electron temperature decrease with the discharge mode transition.

Actinometry study on dissociation fraction in low pressure capactively coupled Ar–O2 mixture plasma

In the given research work, experiments with optical emission spectroscopy combined with actinometry were performed in capactively coupled 13.56 MHz Ar–O2 discharge in the pressure range of 0.2 to 0.5 mbar. The Ar content in the gas mixture was varied from 5 to 30%; effect of the filling gas pressure and Ar content on the variation of emission line intensities from various species, dissociation fraction and electron temperature was investigated at 150 and 250 W input powers. The electron temperature was increased with an increase in Ar content in the mixture and input power, however, a linear decrease in electron temperature was seen with an increase in filling gas pressure. It is worth mentioning here that the electron temperature increased linearly with an increase in Ar content from 5 to 10%, thereafter reached its steady state. The excitation temperature was increased from 0.86 to 1.33 eV with an increase in Ar content from 0 to 30% at 0.2 mbar pressure and 250 W RF power. The presented work concludes that the electron temperature and generation of the active species strongly depend on Ar content in the mixture together with the discharge conditions.

Triple-probe Diagnostic Measurements in Plasma of GLAST Spherical Tokamak

Triple-probe has been developed and operated successfully to characterize ECRH-assisted argon as well as hydrogen microwave plasmas in GLAST Spherical Tokamak. This technique enables to determine transient plasma parameters such as floating potential, electron temperature and electron number density in rapidly time-varying plasmas. An effective electron heating mechanism is applied to produce microwave plasma by injecting radiofrequency (RF) radiation at a frequency of 2.45 GHz in the presence of resonant toroidal magnetic field. Plasma parameters and corresponding fluctuations are measured as a function of time in different gas fill pressures for various applied magnetic fields. The results demonstrate the dependence of plasma parameters such as Vf, Te, ne and their fluctuations on gas fill pressure during the pre-ionization phase of the GLAST operation. Plasma behavior is observed to be closely depending on the coupling of RF power during microwave discharge. Additionally, the hydrogen plasma shows pronounced fluctuations in comparison with argon plasma with some decrease in electron temperature and densities.

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

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

Electron temperature measurement in Maxwellian non-isothermal beam plasma of an ion thruster.

Published electron temperature profiles of the beam plasma from ion thrusters reveal many divergences both in magnitude and radial variation. In order to know exactly the radial distributions of electron temperature and understand the beam plasma characteristics, we applied five different experimental approaches to measure the spatial profiles of electron temperature and compared the agreement and disagreement of the electron temperature profiles obtained from these techniques. Experimental results show that the triple Langmuir probe and adiabatic poly-tropic law methods could provide more accurate space-resolved electron temperature of the beam plasma than other techniques. Radial electron temperature profiles indicate that the electrons in the beam plasma are non-isothermal, which is supported by a radial decrease (∼2 eV) of electron temperature as the plume plasma expands outward. Therefore, the adiabatic "poly-tropic law" is more appropriate than the isothermal "barometric law" to be used in electron temperature calculations. Moreover, the calculation results show that the electron temperature profiles derived from the "poly-tropic law" are in better agreement with the experimental data when the specific heat ratio (γ) lies in the range of 1.2-1.4 instead of 5/3.

On the Plasma Parameters in Co-sputtering Discharge

In this work, a DC planar sputtering system has been successfully designed, manufactured and assembled. The glow discharge plasma chamber was made of stainless steel with a length of 40.5 cm and a diameter of 28 cm. This chamber consists of two Coplanar sputtering magnetrons adapted with copper and Aluminum targets each of diameter of 4.8 cm. The systems have been tested with the pressure of 6x10-5 mbar. The plasma parameters like electron temperature Te, electrons density ne, ions density ni, plasma potential VP and floating potential VF were measured using single Langmuir probe with different gas pressures and distances between the electrodes. It is found that the electron temperature decreases and electron density increased with increasing the argon gas pressure and varying distance between electrodes.

Spectral characteristics of arc plasma during laser-arc double-sided welding for aluminum alloy

In laser-arc double-sided welding, the spectral characteristics of the arc plasma are calculated and analyzed by spectroscopic diagnosis. The results show that, compared with conventional tungsten inert gas (TIG) welding, the introduction of a laser changes the physical characteristics of the arc plasma regardless of whether laser plasma penetration takes place, and that the influence of the laser mainly affects the near-anode region of the arc. When the laser power is relatively low, the arc column tends to compress, and the arc spectral characteristics show no significant difference. When the arc root constricts, compared with pure TIG arc, the electron density increases by ∼2.7 times and the electron temperature decreases by ∼3000 K. When the arc column expands, the intensities of spectral lines of both the metal and Ar atoms are the strongest. But it is also observed that the electron density reduces, whereas there is no obvious decrease of electron temperature. OCIS codes: 140.3390, 350.3390, 300.6170. doi: 10.3788/COL201513.061403.