Values Of Electron Temperature Research Articles

Characterization and calibration of 8-channel E-band heterodyne radiometer system for SST-1 tokamak.

An 8-channel E-band heterodyne radiometer system (74-86 GHz) is designed, characterized, and calibrated to measure the radial electron temperature profile by measuring Electron Cyclotron Emission spectrum at SST-1 Tokamak. The developed radiometer has a noise equivalent temperature of 1 eV and sensitivity of 5 × 10(9) V/W. In order to precisely measure the absolute value of electron temperature, a calibration measurement of the radiometer system is performed using hot-cold Dicke switch method, which confirms the system linearity.

Diagnostic of Plasma Produced by a Spark Plug at Atmospheric Pressure: Reduced Electric Field and Vibrational Temperature

AbstractThe electric discharge generated between the electrodes of a classic spark plug could not assure a fast and total combustion of the air – hydrocarbon mixture. To be able to improve the quality of the combustion process through the ignition system improvement it is necessary to have a complete diagnostic of the discharge produced by a spark plug, from physical and chemical point of view. This work presents a comparative study of the reduced electric field and the vibrational temperature for a classic spark produced in air at atmospheric pressure, as functions of pulses widths applied by the power supply. The reduced electric field was calculated by using the rotational temperature values established by a previous study, considering them as temperature plasma gas temperatures. The vibrational temperature was determined by using the N2second positive molecular emission spectra. The spark plug was supplied with trains of pulses containing one or two pulses having variable widths provided by a special power supply.The results obtained for the vibrational temperature of nitrogen molecules are close to these obtained for the rotational temperature calculated by using a spectroscopic diagnostic method based on the OH UV molecular band spectra (between 2000 and 3500 K). The electron temperature values, imposed by the reduced electric field (up to 2000 Td), are superior to 10000 K. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Plasma Structure of Miniature Ring-Cusp Ion Thruster Discharges

Previous miniature ion thruster studies have demonstrated impressive performance using ring-cusp discharges. These studies suggest that the magnetic field must be sufficiently strong to increase primary electron confinement times for ionization, but weak enough to allow plasma electrons to escape and maintain the plasma potential necessary for ionization. To investigate these phenomena, an experiment was developed to allow detailed measurements of the internal structure and characteristics of a miniature ring-cusp discharge. These measurements provide spatially resolved values for plasma density, electron temperature, and plasma potential along a meridian plane. The magnetic field configuration is arranged as a quasi-periodic domain in order to generalize the findings to all multipole discharges. The results show that the magnetic field strength drives the plasma structure, and the dependence on discharge power can be removed with proper scaling of the plasma parameters. The stronger magnetic field results in a higher peak plasma density, but relatively low discharge utilization efficiency. In addition, the potential measurements indicate the likely onset of discharge instability. In contrast, the weaker magnetic field, or baseline configuration, better uses the volume of the chamber. This leads to a higher and more uniform density near the downstream end of the discharge where ion extraction would occur, implying superior discharge utilization.

Cosmic ray acceleration and Balmer emission from RCW 86 (G315.4 – 2.3)

Context. Observation of Balmer lines from the region around the forward shock of supernova remnants (SNR) may provide valuable information on the shock dynamics and the efficiency of particle acceleration at the shock. Aims. We calculated the Balmer line emission and the shape of the broad Balmer line for parameter values suitable for SNR RCW 86 (G315.4-2.3) as a function of the cosmic-ray (CR) acceleration efficiency and of the level of thermal equilibration between electrons and protons behind the shock. This calculation aims at using the width of the broad Balmer-line emission to infer the CR acceleration efficiency in this remnant. Methods. We used the recently developed nonlinear theory of diffusive shock-acceleration in the presence of neutrals. The semianalytical approach we developed includes a description of magnetic field amplification as due to resonant streaming instability, the dynamical reaction of accelerated particles and the turbulent magnetic field on the shock, and all channels of interaction between neutral hydrogen atoms and background ions that are relevant for the shock dynamics. Results. We derive the CR acceleration efficiency in the SNR RCW 86 from the Balmer emission. Since our calculation used recent measurements of the shock proper motion, the results depend on the assumed distance to Earth. For a distance of 2 kpc the measured width of the broad Balmer line is compatible with the absence of CR acceleration. For a distance of 2.5 kpc, which is a widely used value in current literature, a CR acceleration efficiency of 5-30% is obtained, depending upon the electron-ion equilibration and the ionization fraction upstream of the shock. By combining information on Balmer emission with the measured value of the downstream electron temperature, we constrain the CR acceleration efficiency to be ~20%.

Langmuir probe measurements in a time-fluctuating-highly ionized non-equilibrium cutting arc: Analysis of the electron retarding part of the time-averaged current-voltage characteristic of the probe

This work describes the application of Langmuir probe diagnostics to the measurement of the electron temperature in a time-fluctuating-highly ionized, non-equilibrium cutting arc. The electron retarding part of the time-averaged current-voltage characteristic of the probe was analysed, assuming that the standard exponential expression describing the electron current to the probe in collision-free plasmas can be applied under the investigated conditions. A procedure is described which allows the determination of the errors introduced in time-averaged probe data due to small-amplitude plasma fluctuations. It was found that the experimental points can be gathered into two well defined groups allowing defining two quite different averaged electron temperature values. In the low-current region the averaged characteristic was not significantly disturbed by the fluctuations and can reliably be used to obtain the actual value of the averaged electron temperature. In particular, an averaged electron temperature of 0.98 ± 0.07 eV (= 11400 ± 800 K) was found for the central core of the arc (30 A) at 3.5 mm downstream from the nozzle exit. This average included not only a time-average over the time fluctuations but also a spatial-average along the probe collecting length. The fitting of the high-current region of the characteristic using such electron temperature value together with the corrections given by the fluctuation analysis showed a relevant departure of local thermal equilibrium in the arc core.

Plasma chemistry in the free-burning Ar arc

Recent ambitions have been aimed at modelling of a free-burning arc in argon by means of a self-consistent description of the arc plasma and the electrodes avoiding assumptions of equilibrium. As a next step, the present work deals with the impact of the reaction chemistry used in non-equilibrium modelling. A set of reactions accounts for elastic scattering, excitation and de-excitation in collisions with electrons and atoms, step-wise ionization, recombination and spontaneous emission. A simple chemistry model based on the approximation of prompt ionization, a model with an effective excited level, and a model implying higher excited levels of argon atoms are considered. The results obtained show that all three models are capable of predicting the arc characteristics. They deliver values of electric current density, electric conductivity, arc voltage, electron and heavy particle temperature which are close to each another. The simple model can serve as a fast-track evaluation of the arc characteristics, and for sensitive studies of the impact of model parameters. The extended model allows obtaining the populations of individual and effective levels giving rise to important radiative transitions.

Statistical properties of the surface‐charging environment at geosynchronous orbit

AbstractBased on 13 years of data from the Magnetospheric Plasma Analyzers on six Los Alamos National Laboratory (LANL) geosynchronous satellites, the statistical behavior of environmental conditions that cause strong surface charging on the satellites is examined. Analysis of the Magnetospheric Plasma Analyzers data reveals the electron energy range (~5–10 keV) and threshold flux (1.4×103 cm–2 s–1 sr–1 eV–1 at 8 keV) that are most closely associated with satellite surface charging. We also find that the average ambient electron temperature in the plasma sheet correlates with the observed magnitude of the surface potential on the LANL satellites. Analysis of the statistical occurrence rates of (1) the observed surface potential on the LANL satellites, (2) 8 keV electron fluxes above the threshold, and (3) elevated values of the average electron temperature all reveal that an enhanced surface charging probability exists (a) during higher values of Kp, (b) in the local time range from premidnight through dawn, (c) during equinox seasons, and (d) during the declining phase of the solar cycle. With the exception of the solar cycle dependence, these are the same statistical dependences found by Choi et al. (2011) in the satellite anomaly database they examined. The local time dependence of those anomalies is a particularly strong diagnostic of surface charging as a probable cause of a significant number of them.

Analysis of cylindrical Langmuir probe using experiment and different theories

Cylindrical probe data have been analyzed using different theories in order to determine some plasma parameters (electron temperature and electron and ion densities). Langmuir probe data are obtained in a cylindrical DC glow discharge in the positive column plasma at argon gas pressures varied from 0.5 to 6 Torr and at constant discharge current equal to 10 mA. The electron density has calculated from the elec� tron current at the space potential and from Orbital Motion Limited (OML) collisionless theory. Ion density has obtained from the OML analysis of the ion saturation currents. In addition, the electron temperature has measured by three different methods using probe and electrons currents. The electron temperature Te, plasma density ne, and space potential Vs, have been obtained from the measured single cylindrical probe I- V characteristic curves. The radial distribution of the electron temperature and plasma density along the glow discharge are measured and discussed. Using the collisionless theories by Langmuir cylindrical probe and up to several Torr argon gas pressures the differences between the values of electron temperature and electron and ion densities stay within reasonable error limits.

Temporal behavior of the tungsten plasma produced by 1064 nm pulsed Nd-YAG laser

A time-resolving Langmuir probe was used to investigate the expansion of tungsten plasma produced by the pulsed Nd-YAG laser (wavelength=1064nm, pulse duration=10ns). Current–voltage (IV) plots at various times after the laser shot hit the target were obtained from probe electron and ion currents. Langmuir probe theory was used to determine the temporal variation of the plasma potential, electron temperature and electron density. These plasma parameters sharply rise to a maximum value and then slowly decrease during the plume expansion. For the laser irradiance of 10.88×108W/cm2, maximum values of plasma potential, electron temperature and electron density were about 24V, 15.8eV and 2.24×1016cm−3 respectively. The measurements performed with time-of-flight electrostatic energy analyzer confirmed the presence of highly charged tungsten ions in the plasma and charge state of ions found to increase with the laser irradiance.

Revisiting plasma hysteresis with an electronically compensated Langmuir probe

The measurement of electron temperature in plasma by Langmuir probes, using ramped bias voltage, is seriously affected by the capacitive current of capacitance of the cable between the probe tip and data acquisition system. In earlier works a dummy cable was used to balance the capacitive currents. Under these conditions, the measured capacitive current was kept less than a few mA. Such probes are suitable for measurements in plasma where measured ion saturation current is of the order of hundreds of mA. This paper reports that controlled balancing of capacitive current can be minimized to less than 20 μA, allowing plasma measurements to be done with ion saturation current of the order of hundreds of μA. The electron temperature measurement made by using probe compensation technique becomes independent of sweep frequency. A correction of ≤45% is observed in measured electron temperature values when compared with uncompensated probe. This also enhances accuracy in the measurement of fluctuation in electron temperature as δT(pk-pk) changes by ~30%. The developed technique with swept rate ≤100 kHz is found accurate enough to measure both the electron temperature and its fluctuating counterpart. This shows its usefulness in measuring accurately the temperature fluctuations because of electron temperature gradient in large volume plasma device plasma with frequency ordering ≤50 kHz.

Modelling the black hole silhouette in Sagittarius A* with ion tori

We calculate the "observed at infinity" image and spectrum of the accretion structure in Sgr A*, by modelling it as an optically thin, constant angular momentum ion torus in hydrodynamic equilibrium. The physics we consider includes a two-temperature plasma, a toroidal magnetic field, as well as radiative cooling by bremsstrahlung, synchrotron and inverse Compton processes. Our relativistic model has the virtue of being fully analytic and very simple, depending only on eight tunable parameters: the black hole spin and the inclination of the spin axis to our line of sight, the torus angular momentum, the polytropic index, the magnetic to total pressure ratio, the central values of density and electron temperature and the ratio of electron to ion temperatures. The observed image and spectrum are calculated numerically using the ray-tracing code GYOTO. Our results demonstrate that the ion torus model is able to account for the main features of the accretion structure surrounding Sgr A*.

Measurements of electron density and temperature in the H-1 heliac plasma by helium line intensity ratios

Electron density and temperature distributions in the H-1 heliac plasma are measured using the helium line intensity ratio technique based on a collisional-radiative model. An inversion approach with minimum Fisher regularization is developed to reconstruct the ratios of the local emission radiances from detected line-integrated intensities. The electron density and temperature inferred from the He I 667.8/728.1 and He I 728.1/706.5 nm line ratios are in good agreement with those from other diagnostic techniques in the inner region of the plasma. The electron density and temperature values appear to be a little high in the outer region of the plasma. Some possible causes of the discrepancy in the outer region are discussed.

Electron broadening of the resonance lines of Ar+17 and Ar+16

With the revised UCL wave code, the reactance matrix can be calculated when an electron impacts on an ion, so that the scattering matrix and the collision strength are calculated. With the collision strength, the electron broadening of the resonance line is studied. Specifically, the widths and the shifts of resonance lines emitted from Ar+17 and Ar+16 are calculated under the different values of electron temperature and electron density.

Effect of anisotropy of electron velocity distribution function on dynamic characteristics of sheath in Hall thrusters

In Hall thrusters, the electron velocity distribution function is not only depleted at high energies, but also strongly anisotropic. With these electrons interacting with the channel wall, the sheath will be changed in its dynamic characteristics. In the present letter, a two dimensional particle-in-cell code is used to simulate these effects in a collisionless plasma slab. The simulated results indicate that the sheath changes from steady regime to temporal oscillation regime when the electron velocity distribution function alters from isotropy to anisotropy. Moreover, the temporal oscillation sheath formed by the anisotropic electrons has a much greater oscillating amplitude and a much smaller average potential drop than that formed by the isotropic electrons has. The anisotropic electrons are also found to lower the critical value of electron temperature needed for the appearance of the spatial oscillation sheath.

Spatially resolved dynamic structure factor of finite systems from molecular dynamics simulations

The dynamical response of metallic clusters up to 10(3) atoms is investigated using the restricted molecular dynamics simulations scheme. Exemplarily, a sodium like material is considered. Correlation functions are evaluated to investigate the spatial structure of collective electron excitations and the optical response of laser-excited clusters. In particular, the spectrum of bilocal correlation functions shows resonances representing different modes of collective excitations inside the nano plasma. The spatial structure, the resonance energy, and the width of the eigenmodes have been investigated for various values of electron density, temperature, cluster size, and ionization degree. Comparison with bulk properties is performed and the dispersion relation of collective excitations is discussed.

Electron energetics in the Enceladus torus

[1] The inner magnetosphere of Saturn contains both neutral gas and plasma whose composition is dominated by water group ion species. This gas is distributed in a torus-shaped region located near the orbit of Enceladus. The source of this gas is the predominately water vapor plume located in the south polar region of Saturn's icy satellite Enceladus. The electron distribution in the torus comprises two populations: a relatively cold ( 10 eV) suprathermal tail. This paper describes model calculations of the electron energy distribution and energetics in the torus in order to explore how the observed electron distributions can be explained. A thermal electron energy equation is numerically solved, and electron temperatures are calculated. A separate electron energy deposition model determines suprathermal electron fluxes as functions of energy. The main suprathermal electron population is due to photoelectron production from the absorption of solar radiation by water and other neutral species, and this is demonstrated by a comparison of the model results with recently published Cassini data. The model includes heating of thermalized electrons by fresh photoelectrons and by hot pickup ions and also includes cooling by collisions with water and other neutral species. Calculated electron temperatures for the thermal population are about 104 − 2 × 104 K (i.e., 1–2 eV), values which are somewhat lower than recently published Cassini Langmuir probe electron temperature values of 2–3 eV.

Hot electrons as tracers of large-scale structure of magnetotail current sheets

[1] This paper is devoted to the investigation of the vertical electron temperature distribution in thin currents sheets of the Earth magnetotail. The dependence of electron temperature on magnetic field Te(Bx) is examined for 62 thin currents sheet crossings by the Cluster spacecraft. The profiles Te(Bx) are approximated by the simple expression Te ≈ Temax(1 − α(Bx/Bext)2), where α is a constant parameter, Temax is the maximum value of electron temperature and Bext is the amplitude of Bx obtained from the vertical pressure balance. The mean value of the parameter 〈α〉 ≈ 1. The profiles Te(Bx) are described in the frame of the theory of adiabatic electron heating in the course of the Earthward plasma convection. The comparison between the observed values of α and the theoretical predictions allows to estimate the scale Lx of observed current sheets along the magnetotail (Bz ∼ (−x/Lx)h) and the ratio of Lx and current sheet thickness Lz. For the majority of the observed thin current sheets Lx ∈ [5RE, 20RE] and the average ratio of the scales 〈Lx/Lz〉 ≈ 25.

Ultrashort-laser-pulse absorption with spatial dispersion and nonlocal transport effects

We study ultrashort-laser-pulse absorption and plasma heating at a sharp plasma–vacuum interface using advanced models for all-range plasma permittivity and nonlocal heat transport. The electron response includes both collisional and collisionless dissipative effects in the plasma of an arbitrary ion charge. We show that nonlocal electron heat transport is important for correct determination of the value of electron temperature and spatial temperature profile. Nonlocal electron heat flux comes into play after electrons heat up to temperatures of the order of 1 keV and to temperatures several times less for low-density targets.

Ambipolar ion acceleration in an expanding magnetic nozzle

The helicon plasma stage in the Variable Specific Impulse Magnetoplasma Rocket (VASIMR®) VX-200i device was used to characterize an axial plasma potential profile within an expanding magnetic nozzle region of the laboratory based device. The ion acceleration mechanism is identified as an ambipolar electric field produced by an electron pressure gradient, resulting in a local axial ion speed of Mach 4 downstream of the magnetic nozzle. A 20 eV argon ion kinetic energy was measured in the helicon source, which had a peak magnetic field strength of 0.17 T. The helicon plasma source was operated with 25 mg s−1 argon propellant and 30 kW of RF power. The maximum measured values of plasma density and electron temperature within the exhaust plume were 1 × 1020 m−3 and 9 eV, respectively. The measured plasma density is nearly an order of magnitude larger than previously reported steady-state helicon plasma sources. The exhaust plume also exhibits a 95% to 100% ionization fraction. The size scale and spatial location of the plasma potential structure in the expanding magnetic nozzle region appear to follow the size scale and spatial location of the expanding magnetic field. The thickness of the potential structure was found to be 104 to 105 λDe depending on the local electron temperature in the magnetic nozzle, many orders of magnitude larger than typical laboratory double layer structures. The background plasma density and neutral argon pressure were 1015 m−3 and 2 × 10−5 Torr, respectively, in a 150 m3 vacuum chamber during operation of the helicon plasma source. The agreement between the measured plasma potential and plasma potential that was calculated from an ambipolar ion acceleration analysis over the bulk of the axial distance where the potential drop was located is a strong confirmation of the ambipolar acceleration process.

Combined Nonlinear Tokamak Plasma Current Profile Control System Design and Simulation with Input Constraints

AbstractThe paper presents the design and simulation results of the combined multivariable control system with the plant input constraints for a plasma current profile in a tokamak. The plasma kinetic model was used in terms of the Grad-Shafranov plasma equilibrium equation and the poloidal magnetic flux diffusion equation. The model is square specifically contains 5 inputs and 5 outputs. Actuators are external current drive sources. Output is plasma current density measured at five points of the minor radius. A set of linear models for controller design was obtained by a state subspace identification approach. A set of H∞ controllers was synthesized by a loop shaping methodology at various values of the plasma electron temperature on the magnetic axis. Controllers designed were applied by the numerical simulation to the original model to change the current profile from one state to another. In the presence of plant input constraints a special logic block was developed in addition to the linear robust controller and used when plant inputs saturated. The plasma current profile control system designed showed its operability in the tokamak plasma electron temperature range on the magnetic axis from 0.1 to 18 keV.