Electron Temperature In Region Research Articles

Electron heating and airglow emission due to lightning effects on the ionosphere

This study is the first attempt to consider lightning effects on the F2 region. Although pulsed electric fields parallel to the geomagnetic field have been observed by every rocket flight over active thunderstorms at thermospheric heights, their existence remains controversial. Predicting the disturbance of ionospheric parameters induced by these electric fields may lead to verifying them using ground‐based ionospheric observations. This study is also important for understanding the kinetics of ionospheric plasma disturbed by pulsed parallel electric fields. These fields can accelerate electrons from pulse to pulse. If the pause between flashes is longer than τen, electrons are scattered by elastic collisions with neutrals and transformed into thermal electrons with a corresponding electron temperature enhancement. Inelastic collisions of electrons with neutrals will become more important with increased energy and, subsequently, the electron energy distribution (EED) can differ from a Maxwellian distribution. The vibrational excitation of N2 is extremely important as a source of inelastic collisions for energy ≥2 eV. This vibrational barrier can influence the EED. An electron kinetics model induced by pulsed parallel electric fields in ionospheric plasma is developed here. The accelerated and heated electrons can excite airglow in the F2 region. Excitation of red line emissions is most effective. Red line intensities during thunderstorms are predicted to be much higher than the background intensity. Our model also predicts a significant increase in electron temperature in the F2 region during a strong thunderstorm. Opportunities for observing the ionospheric effects of parallel electric fields induced by lightning are discussed.

Benchmarking atomic data for astrophysics: Fe VII and other cool lines observed by Hinode EIS

The EUV spectrum of is reviewed, using new rates for electron impact excitation, atomic structure calculations, and experimental data. In particular, solar observations of a sunspot loop spectrum obtained from the Hinode EUV Imaging Spectrometer (EIS) are used. Previous line identifications, mostly based on laboratory data, have been assessed. Large discrepancies between observed and predicted line intensities and wavelengths are found for the decays from the 3s<sup>2<sup/> 3p<sup>5<sup/> 3d<sup>3<sup/> configuration, which are strong EUV lines. We ascribe these discrepancies to incorrect line identifications. A number of new identifications are proposed. With these, very good agreement between theory and experimental data is found. A few transitions, in particular from the 3s<sup>2<sup/> 3p<sup>6<sup/> 3d 4s configuration, are observed for the first time, and are shown to provide a new important diagnostic for measuring the electron temperature in the solar transition region. The temperatures obtained at the base of solar coronal loops are found to be close to the temperature of maximum abundance in ionization equilibrium (K). The assessment of the lines was done in conjunction with an assessment of all the strongest cool lines observed with EIS. This spectrum is rich in transition region lines. Some new identifications are presented, in particular for . Most of the strongest transitions are identified, however a large number of lines still awaits firm identification.

Plume detachment from a magnetic nozzle

High-powered electric propulsion thrusters utilizing a magnetized plasma require that plasma exhaust detach from the applied magnetic field in order to produce thrust. This paper presents experimental results demonstrating that a sufficiently energetic and flowing plasma can indeed detach from a magnetic nozzle. Microwave interferometer and probe measurements provide plume density, electron temperature, and ion flux measurements in the nozzle region. Measurements of ion flux show a low-beta plasma plume which follows applied magnetic field lines until the plasma kinetic pressure reaches the magnetic pressure and a high-beta plume expanding ballistically afterward. Several magnetic configurations were tested including a reversed field nozzle configuration. Despite the dramatic change in magnetic field profile, the reversed field configuration yielded little measurable change in plume trajectory, demonstrating the plume is detached. Numerical simulations yield density profiles in agreement with the experimental results.

Unified modelling of near-cathode plasma layers in high-pressure arc discharges

A model of a near-cathode region in high-pressure arc discharges is developed in the framework of the hydrodynamic (diffusion) approximation. Governing equations are solved numerically in 1D without any further simplifications, in particular, without explicitly dividing the near-cathode region into a space-charge sheath and a quasi-neutral plasma. Results of numerical simulation are reported for a very high-pressure mercury arc and an atmospheric-pressure argon arc. Physical mechanisms dominating different sections of the near-cathode region are identified. It is shown that the near-cathode space-charge sheath is of primary importance under conditions of practical interest. Physical bases of simplified models of the near-cathode region in high-pressure arc discharges are analysed. A comparison of results given by the present model with those given by a simplified model has revealed qualitative agreement; the agreement is not only qualitative but also quantitative in the case of an atmospheric-pressure argon plasma at moderate values of the near-cathode voltage drop. The modelling data are compared with results of spectroscopic measurements of the electron temperature and density in the near-cathode region.

EXPERIMENTAL STUDY OF A LOW-VOLTAGE CIRCUIT BREAKER, BY ANALYSIS OF COMPLEX SPECTRA, INCLUDING THE SELF-REVERSED PROFILES OF COPPER RESONANCE LINES

A low-voltage circuit-breaker operating in air is studied by optical emission spectroscopy. An important quantity of copper vapors coming from electrodes is present in the arc plasma. The existence of a central hot emissive region and a peripheral cold region is brought to the fore. Time evolution of the electron density and temperature in the emissive region were obtained from intensities and profiles of CuI and CuII lines.

Confinement improvement in high-ion temperature plasmas heated with high-energy negative-ion-based neutral beam injection in the Large Helical Device

An increase in the ion temperature due to transport improvement has been observed in plasmas heated with high-energy negative-ion-based neutral beam injection (NBI), in which the electrons are dominantly heated, in the Large Helical Device. When centrally focused electron-cyclotron-resonance heating is superposed on the NBI plasma, the ion temperature is observed to rise, accompanied by the formation of the electron internal transport barrier (electron-ITB). In the electron-ITB plasmas, an increase in a positive radial electric field is observed, and the transport analysis indicates that the ion transport in the half-radius region is improved with a reduction of the anomalous transport. Thus, this ion temperature rise is ascribed to the ion transport improvement by the transition to the neoclassical electron root. In high-Z plasmas, the ion temperature is increased with an increase in the ion heating power and reaches 13.5 keV. The central ion temperature increases with an increase in a gradient of the electron temperature in an outer plasma region of ρ = 0.8, suggesting the ion transport improvement in the outer plasma region induced by the neoclassical electron root. These results indicate the effectiveness of the electron-root scenario for obtaining high-ion temperature plasmas in helical systems.

Spatial structures of plasma parameters in a magnetic neutral loop discharge

Spatial structures of plasma parameters in a radio-frequency inductively coupled magnetic neutral loop discharge are investigated under various parameter variations using spatially resolved Langmuir probe measurements. A strong coupling between the plasma production region, in the neutral loop (NL) plane, and the axially remote substrate region is observed. The two regions are connected through the separatrices and therefore, spatial profiles in the substrate region are strongly influenced by the plasma production region and the structure of the separatrices. The electron temperature in the plasma production region peaks in the centre of the NL while the maximum in electron density is shifted radially inwards due to diffusion. Details of the structures in both regions, the production region and the substrate region, are determined through the position of the NL and the gradient of the inhomogeneous magnetic field around the NL confinement region. Parameter combinations are found providing higher plasma densities and better uniformity than in common inductively coupled plasmas without applying an additional magnetic field. The uniformity can be further improved using temporal variations of the magnetic field structure.

The Electron Temperature Gradient in the Galactic Disk

We derive the electron temperature gradient in the Galactic disk using a sample of HII regions that spans Galactocentric distances 0--17 kpc. The electron temperature was calculated using high precision radio recombination line and continuum observations for more than 100 HII regions. Nebular Galactocentric distances were calculated in a consistent manner using the radial velocities measured by our radio recombination line survey. The large number of nebulae widely distributed over the Galactic disk together with the uniformity of our data provide a secure estimate of the present electron temperature gradient in the Milky Way. Because metals are the main coolants in the photoionized gas, the electron temperature along the Galactic disk should be directly related to the distribution of heavy elements in the Milky Way. Our best estimate of the electron temperature gradient is derived from a sample of 76 sources for which we have the highest quality data. The present gradient in electron temperature has a minimum at the Galactic Center and rises at a rate of 287 +/- 46 K/kpc. There are no significant variations in the value of the gradient as a function of Galactocentric radius or azimuth. The scatter we find in the HII region electron temperatures at a given Galactocentric radius is not due to observational error, but rather to intrinsic fluctuations in these temperatures which are almost certainly due to fluctuations in the nebular heavy element abundances. Comparing the HII region gradient with the much steeper gradient found for planetary nebulae suggests that the electron temperature gradient evolves with time, becoming flatter as a consequence of the chemical evolution of the Milky Way's disk.

Flow Energy Control of Nitrogen Ions Generated by Electron Cyclotron Resonance

The flow energy of nitrogen ions produced by an electron cyclotron resonance (ECR) discharge is controlled by electrostatic acceleration in a plasma synthesis method. The source consists of an ion production region using ECR and a plasma synthesis region. Two grids for potential control and electron reflection of the ion production region, and an electron emitter with mesh shape are installed. In the synthesis region, electrons emitted from the emitter and ions accelerated by electrostatic potential difference between these regions are synthesized, which yields the generation of ion flow in the synthesis region. The electron temperature in the plasma synthesis region can be reduced to about 0.5 eV because of a reflection of high-energy electrons in the ion production region and a supply of thermionic electrons. In addition, it is observed that the density ratio of nitrogen atomic to molecular ions in the synthesis region markedly increases compared with that in the ion production region.

Investigation of pinching discharges in MPC device operating with nitrogen and xenon gases

Discharge characteristics and parameters of plasma streams generated by magnetoplasma compressor (MPC) of compact geometry with conical-shaped electrodes and pulsed gas supply are studied for different operation regimes. The current — voltage characteristics of the discharge and dependencies of plasma stream velocity on discharge current are analyzed. It is shown that Ud(Id) ∼ aIdb, where b depends on mass flow rate of working gas and time delay between start of gas supply and discharge switching on. Optimal operation regimes are characterized by b ∼ 3. The high-speed imaging the plasma discharge and compression dynamics is carried out in frame-by-frame regime with different absorption optical filters. Spectroscopy measurements of plasma density and electron temperature in compression region of MPC have been performed on the base of Stark broadening of spectral lines and intensities ratio in visible wave-range. Efficiency of MPC operation with nitrogen and xenon gases and influence of the kind of working gas on parameters of compression region are analyzed.

On collisionless ion and electron populations in the magnetic nozzle experiment (MNX)

The Magnetic Nozzle Experiment (MNX) is a linear magnetized helicon-heated plasma device, with applications to advanced spacecraft-propulsion methods and solar-corona physics. This paper reviews ion and electron energy distributions measured in MNX with laser-induced fluorescence (LIF) and probes, respectively. Ions, cold and highly collisional in the main MNX region, are accelerated along a uniform magnetic field to sonic then supersonic speeds as they exit the main region through either mechanical or magnetic apertures. A sharp decrease in density downstream of the aperture(s) helps effect a transition from collisional to collisionless plasma. The electrons in the downstream region have an average energy somewhat higher than that in the main region. From LIF ion-velocity measurements, we find upstream of the aperture a presheath of strength Deltaphi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ps</sub> = <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mr</sub> T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> , where <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mr</sub> T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> is the electron temperature in the main region, and length ~3 cm, comparable to the ion-neutral mean-free-path; immediately downstream of the aperture is an electrostatic double layer of strength Deltaphi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DL</sub> =3-10 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mr</sub> T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> and length 0.3-0.6 cm, 30-600lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> . The existence of a small, ca. 0.1%, superthermal electron population with average energy ~10 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mr</sub> T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> is inferred from considerations of spectroscopic line ratios, floating potentials, and Langmuir probe data. The superthermal electrons are suggested to be the source for the large Deltaphi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DL</sub>

Effect of magnetic field profile on the anode fall in a Hall-effect thruster discharge

The effect of the magnetic field configuration on the anode fall in an E⃗×B⃗ discharge of a Hall thruster is studied both experimentally and theoretically. Plasma potential, electron temperature, and plasma density in the near-anode region are measured with a biased probe in three configurations of the magnetic field. It is observed that the anode fall in a Hall thruster can be changed from negative to positive by creating a magnetic field configuration with a zero magnetic field region. Similar configurations are utilized in some advanced Hall thrusters, like an ATON thruster. Results of the measurements are employed to model a Hall thruster with different magnetic field configurations, including the one with a zero-field region. Different anode sheath regimes observed experimentally are used to set the boundary conditions for the quasineutral plasma. Numerical solutions obtained with a hydrodynamic quasi-one-dimensional model suggest that varying the magnetic field configuration affects the electron mobility both inside and outside the channel, as well as the plasma density distribution along the axis.

Study of an edge transport barrier by Langmuir probes in the compact helical system

The edge transport barrier (ETB) produced by the L–H transition was measured by a triple Langmuir probe (LP) at two toroidal sections of the compact helical system (CHS), of which diagnostic method has good time and spatial resolutions. The radial profiles of electron density (ne), electron temperature (Te) and space potential (Vs) in the ETB region have different shapes at two different toroidal sections. These profiles are deformed inside the ETB region at one location and are formed with rather smooth variations at the other. These deformations gradually disappear in the deep H-phase (after ∼15 ms from the transition) and the profiles inside the ETB become similar at both sections. The deformation seems linked to the presence of a non-rotating magnetic island at the rational surface of the rotational transform ι/2π = 1.

Analytical solution for temperature field in electron and lattice sub-systems during heating of solid film

The analytical solution for non-equilibrium temperature field in solid substrate is presented. Closed form solutions for electron and lattice site temperature rise are obtained for a solid layer heated at the surface with a time-decaying intensity pulse. In the analytical solutions, a perturbation method of strained parameters is introduced. Temperature simulations are carried out for a gold layer with different thicknesses. It is found that increasing layer thickness lowers electron and lattice site temperatures at the surface. Electron temperature at the surface decays sharply with progressing heating period, which is more pronounced for thin layer. Moreover, lattice site temperature continues to rise despite reducing electron temperature in the surface region. The results obtained from the analytical solution for the lattice site temperature agrees well with the numerical predictions.

Observing the north polar ionosphere on 30 October 2003 by GPS imaging and IS radars

Abstract. The evening of 30 October 2003 was subject to a major storm main phase. For this time, we combine large-scale electron content maps from GPS imaging with time series of electron density and temperature of two EISCAT radars in Tromsø and Svalbard and the Sondrestrom radar, for observing the north polar ionosphere. The GPS assimilations resulted in the image of the electron content trace of an anti-sunward polar Tongue Of Ionisation (TOI) consecutively to 20:00 UT. In combination with the radar observations we concluded that the TOI persisted during the whole period of continuous southward IMF Bz until about 22:40 UT while its largest extension toward the nightside auroral region was found between 21:00-22:00 UT. A typical F region electron temperature of ~2000 K and the plasma velocity of ~800 ms-1 support its convective origin from the dayside mid-latitudes. Due to the structured appearance of the electron content distribution and the radar electron density time series we believe that discrete plasma patches formed inside the anti-sunward drift pattern. After two large oscillations of the IMF Bz the nightside plasma density was observed to re-enhance after 23:00 UT along a longitudinal band below 70 N. Coinciding electron temperatures of ~2000 K suggest again the convective nature of the plasma, while a modified convection pattern is expected.

Particle growth in hydrogen–methane plasmas

Particle growth and the behavior of particle clouds in hydrogen–methane capacitively coupled rf plasmas are investigated. At room temperature, most for different wall temperatures and gas compositions of these particles are due to flakes of layers delaminated from the electrode surfaces. Heating of the electrodes up to 800 K and dilution by hydrogen (up to H 2:CH 4 = 20:1) suppresses the production of the particles from the electrode surfaces. The electron temperature in the particle levitation region is controlled by introducing an additional electrode made from a grid (= gridded electrode) in between the levitation electrode and the driven electrode. If we introduce diamond seed particles (∼ 2.8 μm in diameter) into the plasma with the gridded electrode in place, we observe nucleation of new grains (∼ 100 nm) on the surfaces of the diamond particles. On the other hand, without the gridded electrode, we do not observe nucleation but growth of amorphous carbon films on them.

Control and analysis of ion species in inductively coupled nitration plasma using a grid system

We control the ion density ratio of [N+]∕[N2+] with the voltage-biased grid system in inductively coupled nitration plasma. The ion density ratio is controlled from 0.39 to 0.04 with decreasing grid-biased voltage. We try to analyze the variation of the ion density ratio using the measured plasma parameters and particle balance equation. The important factor determining the ion ratio is the plasma potential difference between the source region—where plasma is generated—and the diffusion region—where the electron temperature is controlled. When the plasma potential is higher in the source region than in diffusion region, the ion density ratio is determined by the electron temperature in Region I. Inversely, the ion density ratio is determined by the electron temperature in Region II, when the plasma potential is higher in Region II than in Region I.

Thomson scattering from laser-produced gold plasmas in radiation conversion layer

With a 263.3 nm probe laser beam, the Thomson scattering (TS) spectra are measured at the distance from the surface of gold disc targets as close as 50μm. All of the TS spectra become narrower with time, which indicates the overall drop of plasma temperature as the high-Z plasmas blow off. The experimental data show that there are distinct characteristics between the inner region (i.e., 50 and 100μm away from target surface) and the outer region. The gradient of the electron temperature in outer region is toward the target and becomes opposite to that in the inner region. The asymmetries of the TS spectra in the inner region are in good agreement with calculation based on the Spitzer–Härm theory. In the outer region, however, the discrepancies between the experiments and calculations are significant, which may be a hint that the electron energy transport becomes flux limited or nonlocal in this region.

R&D on a high energy accelerator and a large negative ion source for ITER

R&D pertaining to a 1 MeV accelerator and a large negative ion source has been carried out at the Japan Atomic Energy Research Institute for the ITER neutral beam system. The R&D is, at present, progressing towards: (1) 1 MeV acceleration of H− ion beams at the ITER relevant current density of 200 A m−2 and (2) improvement of uniform negative ion production over wide extraction area in large negative ion sources. Recently, H− ion beams of 1 MeV and 140 mA level have been generated with a substantial beam current density (100 A m−2). In the uniformity study, it was clarified that the electron temperature in the ion extraction region was locally high (>1 eV), which resulted in the destruction of negative ions at a high reaction rate. Interception of fast electrons leaking through a transverse magnetic field called ‘magnetic filter’ has been found to be effective in lowering the local electron temperature, followed by an improvement of negative ion beam profile.

A strong positive phase of ionospheric storms observed by the Millstone Hill incoherent scatter radar and global GPS network

During geomagnetic storms, the ionospheric F region electron density may be greatly increased or decreased, which are termed positive storms or negative storms. It is generally accepted that negative storm phases are caused by neutral composition changes. In contrast, different mechanisms have been proposed to explain the generation of positive storm phases. In this paper, we present observations of a strong positive storm at middle latitudes. The Millstone Hill incoherent scatter radar detected significant increases of the midlatitude ionospheric F region electron density during a magnetic storm on 3 April 2004. The positive phase of the ionospheric storm started to occur in the morning sector (0912 LT at Millstone Hill) and lasted for more than 10 hours. Compared with the quiet‐time ionosphere, the daytime F peak altitude over Millstone Hill during the storm was ∼80 km higher, the F region electron density was increased by a factor of 2–4, and the F region electron temperature was decreased by ∼1000 K (or ∼40%). The radar also measured an enhanced eastward electric field and a slightly more equatorward neutral wind. Global GPS measurements show that total electron content (TEC) was increased at middle latitudes and decreased at lower latitudes, and the large TEC enhancements occurred primarily in the Atlantic sector. We suggest that electric fields may play an important role in the generation of the observed positive storm phase. The eastward electric field will cause increases in the midlatitude ionospheric electron density by moving the plasma particles upward and decreases in the equatorial ionospheric electron density by strengthening the fountain effect. The daytime poleward wind was reduced or even reversed during the storm, which may also contribute to the occurrence of the positive storm.