Average Electron Temperature Research Articles

Results from radiating divertor experiments with RMP ELM suppression and mitigation

The range in density and collisionality for which resonant magnetic perturbations (RMPs) are effective in suppressing edge-localized modes (ELMs) in the presence of a radiating divertor was found to be modest for representative H-mode plasmas in DIII-D. When deuterium and argon gas injection rates were increased during RMP, both the electron collisionality in the pedestal and the maximum electron pressure gradient (∇Pe,MAX) in the pedestal also increased. As ∇Pe,MAX approached values consistent with the peeling–ballooning stability limit, as determined by edge stability analysis, ELMing activity re-emerged. For cases with the same injected neutral beam power, argon accumulation in the main plasma was greater in the RMP ELM-suppressed cases than in comparable non-RMP ELMing H-mode cases. Reductions in the core concentration of injected argon were observed for both RMP and non-RMP H-mode cases when their respective deuterium injection rates were increased. Although complete ELM suppression in RMP radiating divertor plasmas in DIII-D was only accessible over a limited range in pedestal density and collisionality, significant ELM mitigation with heat flux reduction was possible over a wider range. Comparing RMP radiating divertor discharges after the re-appearance of ELMing activity during gas puffing with a standard ELMing plasma for cases with the same pedestal density reveals that the RMP discharges have (1) lower average electron temperature at the midplane separatrix, implying lower average electron temperature at the divertor target, (2) lower time-averaged peak heat flux and (3) lower transient peak heat flux from ELMs even at the same pedestal collisionality.

Characterization of the evolution of underwater DBD plasma jet

An air plasma jet formed underwater using a coaxial DBD electrode configuration with gas flow is being studied for water treatment applications. The arc-like behavior of the discharge in the absence of any obvious return electrode is not well understood. This study seeks to understand the underlying nature of the arc-like jet mode by studying the evolution of the discharge from microdischarge to jet mode. Photographic and spectroscopic data are used to develop a phenomenological model of discharge evolution. Time-averaged spectra were used to assign an average plume and electron temperature. Calculated jet temperatures were consistent with observed affects such as melting and oxide layer formation on a downstream substrate. The capacity of the microdischarge mode to decompose organic dye in water as a function of time, confirmed previously in the jet mode, was also demonstrated in the absence of the jet.

Nanomaterials synthesis at atmospheric pressure using nanosecond discharges

The application of nanosecond discharges towards nanomaterials synthesis at atmospheric pressure is explored in this perspective article. First, various plasma sources are evaluated in terms of the energy used to include one atom into the nanomaterial, which is shown to depend strongly on the electron temperature. Because of their high average electron temperature, nanosecond discharges could be used to achieve nanofabrication at a lower energy cost, and therefore with better efficiency, than with other plasma sources at atmospheric pressure. Transient spark discharges and nanosecond repetitively pulsed (NRP) discharges are suggested as particularly useful examples of nanosecond discharges generated at high repetition frequency. Nanosecond discharges also generate fast heating and cooling rates that could be exploited to produce metastable nanomaterials.

Electron density and temperature of gas-temperature-dependent cryoplasma jet

A microsize cryoplasma jet was developed and analyzed at plasma gas temperatures ranging from room temperature down to 5 K. Experimental results obtained from optical emission spectroscopy and current–voltage measurements indicate that the average electron density and electron temperature of the cryoplasma jet depend on the gas temperature. In particular, the electron temperature in the cryoplasma starts to decrease rapidly near 60 K from about 13 eV at 60 K to 2 eV at 5 K, while the electron density increases from about 109 to approximately 1012 cm−3 from room temperature to 5 K. This phenomenon induces an increase in the Coulomb interaction between electrons, which can be explained by the virial equation of state.

Analytical Calculation of Gas Temperature and Experimental Determination of Electron Temperature in Gas Discharge in Ne–He Mixtures

Thermal conductivities of binary gas systems are calculated on the basis of existing experimental data and of 12-6 Lennard-Jones and rigid-sphere interatomic interaction approximations for the case of gas discharge in Ne-He mixtures. Assuming that the gas temperature varies only in the radial direction and using the calculated thermal conductivities, an analytical solution of the steady-state heat conduction equation is found for uniform power input. Two cases are considered: taking or not taking into account the radiance of a ceramic tube insert. Measurement of the relative intensities of some He and Ne spectral lines, originating from different upper levels, has enabled us to determine the average electron temperature, using a line-ratio method of optical emission spectroscopy.

Evaluation of Electron Temperature Fluctuations Using Two Different Probe Techniques in Plasma Assembly for Nonlinear Turbulence Analysis (PANTA)

Electron temperature fluctuations are measured with a rotatable triple probe in PANTA. Effects of fluctuation phase are cancelled by aligning the probe pins in the propagation direction of fluctuations. Evaluated electron temperature fluctuations normalized by average electron temperature are much smaller than normalized density fluctuations and normalized floating potential fluctuations in low electron temperature PANTA plasma. Additionally conditional sampling technique is applied to a single probe measurement.

Energy Loss of the Electron System in Individual Single-Walled Carbon Nanotubes

We characterize the energy loss of the nonequilibrium electron system in individual metallic single-walled carbon nanotubes at low temperature. Using Johnson noise thermometry, we demonstrate that, for a nanotube with Ohmic contacts, the dc resistance at finite bias current directly reflects the average electron temperature. This enables a straightforward determination of the thermal conductance associated with cooling of the nanotube electron system. In analyzing the temperature- and length-dependence of the thermal conductance, we consider contributions from acoustic phonon emission, optical phonon emission, and hot electron outdiffusion.

Analytical calculation of the gas temperature and measurement of the electron temperature for gas discharges in Ne and He mixtures with copper, bromine, hydrogen and strontium

Thermal conductivities of binary gas systems are calculated on the basis of 12-6 Lennard-Jones and rigid sphere inter-atomic interaction approximations for the case of gas discharges in He and Ne with small admixtures of copper, bromine, hydrogen and strontium. Assuming that the gas temperature varies only in the radial direction and using the calculated thermal conductivities, analytical solutions of the steady-state heat conduction equation are found for two cases of uniform and non-uniform power input, respectively. For both cases the average gas temperature is found by averaging the radial gas temperature distribution over the radius. Measurement of the relative intensities of some He and Ne spectral lines originating from different upper levels has enabled us to determine the average electron temperature.

Theoretical and experimental determination of gas and electron temperatures for gas discharges in Ne and He mixtures with copper, bromine, hydrogen and strontium

Thermal conductivities of binary gas systems are calculated on the basis of 12-6 Lennard-Jones and rigid sphere inter-atomic interaction approximations for the case of gas discharges in He and Ne with small admixtures of copper, bromine, hydrogen and strontium. Assuming that the gas temperature varies only in the radial direction and using the calculated thermal conductivities, an analytical solution of the steady-state heat conduction equation is found for two discharge tube constructions. Two cases of uniform and non-uniform power input are considered. For both cases the average gas temperature is found by averaging the radial gas temperature distribution over the radius. Measurement of the relative intensities of some He and Ne spectral lines, originating from different upper levels, has enabled us to determine the average electron temperature.

Experimental Investigation into Characteristics of Plasma Aerodynamic Actuation Generated by Dielectric Barrier Discharge

This article carries out synthetic measurements and analysis of the characteristics of the asymmetric surface dielectric barrier discharge plasma aerodynamic actuation. The rotational and vibrational temperatures of an N2(C3IIu) molecule are measured in terms of the optical emission spectra from the N2 second positive system. A simplified collision-radiation model for N2(C) and N2+ (B) is established on the basis of the ratio of emission intensity at 391.4 nm to that at 380.5 nm and the ratio of emission intensity at 371.1 nm to that at 380.5 nm for calculating temporal and spatial averaged electron temperatures and densities. Under one atmosphere pressure, the electron temperature and density are on the order of 1. 6 eV and 1011 cm−3 respectively. The body force induced by the plasma aerodynamic actuation is on the order of tens of mN while the induced flow velocity is around 1. 3 m/s. Starting vortex is firstly induced by the actuation; then it develops into a near-wall jet, about 70 mm downstream of the actuator. Unsteady plasma aerodynamic actuation might stimulate more vortexes in the flow field. The induced flow direction by nanosecond discharge plasma aerodynamic actuation is not parallel, but vertical to the dielectric layer surface.

Application of a collisinal-radiative model for the analysis of K-shell line spectra emitted by Z-pinch plasma

In this paper, the principle of the collisional-radiative model for the estimation of plasma parameters from the ratios of K-shell spectral lines was introduced. The structure of a computer program, ZSPEC, developed for the analysis of K-shell line spectra emitted by Z-pinch plasma based on the collisioanl-radiative model was described in detail. The calculation for neon plasma were presented, including the number fractions of major ionization stages at different electron temperature and the contours of K-shell line ratios in the plane defined by electron density and electron temperature. ZSPEC had been used to analyze the measured results of neon gas-puff Z-pinch experiment performed on Yang accelerator. By comparing the K-shell line ratios of neon plasma obtained by an elliptical crystal spectrometer with the results calculated by ZSPEC, the time and space averaged electron temperature and electron density of the K-shell plasma for the shot with 540 kA peaking current were determined to be 240 eV and 1.0×1019 cm-3, respectively.

Simulation of Plasma Parameters for HCSB-DEMO by a 1.5D Plasma Transport Code

Simulation of the core plasma parameters of HCSB-DEMO (helium-cooled solid breeder, HCSB), by using a 1.5D plasma transport code, was carried out. The study includes investigations of operational scenarios, temperature and density profiles of both ions and electrons, fusion and radiated power, distribution of the safety factor, sensitivity analyses for some input parameters as well as a primary estimate of the divertor heating load. The results indicate that the following fusion reactor parameters can be properly set for HCSB-DEMO, namely major radius of 7.2 m, aspect ratio of 3.4, elongation of 1.85, triangularity of 0.45, plasma current of 14.8 MA, normalized beta of 4.4, toroidal field (TF) of 6.86 T, average electron density of 1.5×1020 m−3, average electron temperature of 14.5 keV, fusion power of 2.55 GW, neutron wall loading of 2.3 MW·m−2 and fusion multiplication factor of 35.

Transport of energy by ultraintense laser-generated electrons in nail-wire targets

Nail-wire targets (20 μm diameter copper wires with 80 μm hemispherical head) were used to investigate energy transport by relativistic fast electrons generated in intense laser-plasma interactions. The targets were irradiated using the 300 J, 1 ps, and 2×1020 W⋅cm−2 Vulcan laser at the Rutherford Appleton Laboratory. A spherically bent crystal imager, a highly ordered pyrolytic graphite spectrometer, and single photon counting charge-coupled device gave absolute Cu Kα measurements. Results show a concentration of energy deposition in the head and an approximately exponential fall-off along the wire with about 60 μm 1/e decay length due to resistive inhibition. The coupling efficiency to the wire was 3.3±1.7% with an average hot electron temperature of 620±125 keV. Extreme ultraviolet images (68 and 256 eV) indicate additional heating of a thin surface layer of the wire. Modeling using the hybrid E-PLAS code has been compared with the experimental data, showing evidence of resistive heating, magnetic trapping, and surface transport.

90 GHz AND 150 GHz OBSERVATIONS OF THE ORION M42 REGION. A SUBMILLIMETER TO RADIO ANALYSIS

We have used the new 90 GHz MUSTANG camera on the Robert C. Byrd Green Bank Telescope (GBT) to map the bright Huygens region of the star-forming region M42 with a resolution of 9'' and a sensitivity of 2.8 mJy beam−1. Ninety GHz is an interesting transition frequency, as MUSTANG detects both the free–free emission characteristic of the H ii region created by the Trapezium stars, normally seen at lower frequencies, and thermal dust emission from the background OMC1 molecular cloud, normally mapped at higher frequencies. We also present similar data from the 150 GHz GISMO camera taken on the IRAM 30 m telescope. This map has 15'' resolution. By combining the MUSTANG data with 1.4, 8, and 21 GHz radio data from the VLA and GBT, we derive a new estimate of the emission measure averaged electron temperature of Te = 11376 ± 1050 K by an original method relating free–free emission intensities at optically thin and optically thick frequencies. Combining Infrared Space Observatory–long wavelength spectrometer (ISO–LWS) data with our data, we derive a new estimate of the dust temperature and spectral emissivity index within the 80'' ISO–LWS beam toward Orion KL/BN, Td = 42 ± 3 K and βd = 1.3 ± 0.1. We show that both Td and βd decrease when going from the H ii region and excited OMC1 interface to the denser UV shielded part of OMC1 (Orion KL/BN, Orion S). With a model consisting of only free–free and thermal dust emission, we are able to fit data taken at frequencies from 1.5 GHz to 854 GHz (350 μm).

Generation control of fast electron beam by low-density foam for FIREX-I

Integrated simulations for fast ignition with a cone-guided target and a 10 ps heating laser have been performed to investigate core heating properties in FIREX-I experiments. It is found that the fast electron beam intensity scales well as the inverse square root of the front electron density, and the averaged core temperature reaches a higher value when the preformed plasma on an inner surface of the cone tip has a longer scale length. As the scale length of the preformed plasma is not easily controllable, a low-density foam coated target is proposed to prevent the reduction in the fast electron beam intensity during the laser irradiation. Optimum foam density and thickness are estimated by averaged core electron temperatures calculated by the integrated simulations.

A NEW APPROACH TO ANALYZING SOLAR CORONAL SPECTRA AND UPDATED COLLISIONAL IONIZATION EQUILIBRIUM CALCULATIONS. II. UPDATED IONIZATION RATE COEFFICIENTS

We have re-analyzed Solar Ultraviolet Measurement of Emitted Radiation (SUMER) observations of a parcel of coronal gas using new collisional ionization equilibrium (CIE) calculations. These improved CIE fractional abundances were calculated using state-of-the-art electron–ion recombination data for K-shell, L-shell, Na-like, and Mg-like ions of all elements from H through Zn and, additionally, Al- through Ar-like ions of Fe. They also incorporate the latest recommended electron impact ionization data for all ions of H through Zn. Improved CIE calculations based on these recombination and ionization data are presented here. We have also developed a new systematic method for determining the average emission measure (EM) and electron temperature (Te) of an isothermal plasma. With our new CIE data and a new approach for determining average EM and Te, we have re-analyzed SUMER observations of the solar corona. We have compared our results with those of previous studies and found some significant differences for the derived EM and Te. We have also calculated the enhancement of coronal elemental abundances compared to their photospheric abundances, using the SUMER observations themselves to determine the abundance enhancement factor for each of the emitting elements. Our observationally derived first ionization potential factors are in reasonable agreement with the theoretical model of Laming.

Crystallographic effects in the kinetic excitation of metal surfaces: A computational study

We present a statistical investigation of the kinetic excitation in atomic collision cascades induced by keV particle impact on metal surfaces. For the model system 5-keV Ag→Ag and a set of 120 impact points, we study the effect of the crystallographic orientation of the target on the average electron temperature evolution at the very surface. Results are discussed in view of secondary ion formation.

A cold plasma plume with a highly conductive liquid electrode

A cold dielectric barrier discharge (DBD) plasma plume with one highly conductive liquid electrode has been developed to treat thermally sensitive materials, and its preliminary discharging characteristics have been studied. The averaged electron temperature and density is estimated to be 0.6eV and 1011/cm3, respectively. The length of plasma plume can reach 5 cm with helium gas (He), and the conductivity of the outer electrode affects the plume length obviously. This plasma plume could be touched by bare hand without causing any burning or painful sensation, which may provide potential application for safe aseptic skin care. Moreover, the oxidative particles (e.g., OH, O*, O3) in the downstream oxygen (O2) gas of the plume have been applied to treat the landfill leachate. The results show that the activated O2 gas can degrade the landfill leachate effectively, and the chemical oxygen demand (COD), conductivity, biochemical oxygen demand (BOD), and suspended solid (SS) can be decreased by 52%, 57%, 76% and 92%, respectively.

On the use of the metallic nozzle of a cutting arc torch as a Langmuir probe

The region inside the nozzle (bore diameter ≈ 1 mm) of a cutting arc torch is inaccessible to most plasma diagnostics, and numerical simulations are the only means to find out the relative importance of several physical processes. In this work, a study of electrostatic (Langmuir) probes applied to the inside of a high energy density 30 A cutting arc torch nozzle is presented. The metallic nozzle was used as a Langmuir probe, so the plasma flow is not perturbed by the probe as a solid body. Biasing the nozzle through an electric circuit that employs appropriate resistors together with the arc power source, the i–V nozzle characteristic was built. It was found that under a large positively biased nozzle, the electron current drained from the arc was relatively small, ≈ 1 A, notwithstanding the fact that the size of the nozzle was relatively large. On the other hand, an almost linear ion current was found for the ion branch for nozzle voltages well below the floating value. Based on the magnitude of inverse slope of the ion current, an estimation of the average electron temperature of the plasma in the vicinity of the nozzle wall was estimated from an ion sheath resistance model using a non-equilibrium two-temperature Saha-equation. An average electron temperature of about 4200 K and a corresponding plasma density of 4 × 1017 m- 3 were found.

X-ray spectral measurements and collisional-radiative modeling of hot, gold plasmas at the omega laser

M-Band and L-Band Gold spectra between 3 and 5 keV and 8 and 13 keV, respectively, have been recorded by a photometrically calibrated crystal spectrometer. The spectra were emitted from the plasma in the laser deposition region of a ‘hot hohlraum’. This is a reduced-scale hohlraum heated with ≈9 kJ of 351 nm light in a 1 ns square pulse at the OMEGA laser. The space- and time-integrated spectra included L-Band line emission from Co-like to Ne-like gold. The three L-Band line features were identified to be the 3s → 2p, 3d 5/2 → 2p 3/2 and 3d 3/2 → 2p 1/2 transitions at ≈9 keV, ≈10 keV and ≈13 keV, respectively. M-Band 5f → 3d, 4d → 3p, and 4p → 3s transition features from Fe-like to P-like gold were also recorded between 3 and 5 keV. Modeling from the radiation–hydrodynamics code LASNEX, the collisional-radiative codes FLYCHK and SCRAM, and the atomic structure code FAC were used to model the plasma and generate simulated spectra for comparison with the recorded spectra. Through these comparisons, we have determined the average electron temperature of the emitting plasma to be between 6.0 and 6.5 keV. The electron temperatures predicted by LASNEX appear to be too large by a factor of about 1.5.