He(I) and He(II) populations in the Nagoya TPD plasma machine

A collisional-radiative model is used to explain the He(I) population densities observed by Otsuka, Ikee and Ishii in their TPD plasma machine. It is shown that a plasma model, which is partially optically thick to He(II) Lyman radiation, can explain the experimentally observed He(II) population density at T_e=3.17 eV. The agreement between the experimental and calculated He(II) population densities observed by Otsuka and others is shown to be due to an error in their calculations.     

Stepwise ionization in a non-equilibrium,steady-state hydrogen plasma

The paper considers a non-equilibrium, steady-state hydrogen plasma with 10¹⁰ ? N_e, cm^-3 ? 10¹⁷ and 8000 ? T_e, °K ? 64,000. The following two cases are analyzed: (1) the plasma is optically thin for all atomic lines and (2) the plasma is optically thick towards the Lyman lines and optically thin for all other lines. Analytical expressions have been obtained for populations and ionization frequencies of excited levels. Populations of the excited levels obtained from the analytical formulas are in good agreement with numerical calculations.     

Saha decrements and collisional-radiative recombination and ionization coefficients for a nonequilibrium oxygen plasma

Using a time-dependent approach, a collisional-radiative model is developed for an oxygen plasma. Effective recombination and ionization coefficients are calculated for two specific cases, optically thin and optically thick in bound-bound u.v. radiation. The steady-state population densities for neutral and ionic states are presented in terms of their deviations from Saha equilibrium predictions. These results show the approach of the plasma to a state of local thermodynamic equilibrium (LTE) as a function of electron temperature and density. The computations are for temperatures between 1.0 and 3.0 eV and electron densities between 10¹⁶ and 10¹⁹ cm^-3.     

Direct observation of population inversion between Al+11 levels in a laser-produced plasma

Measured X-ray intensities of the resonance line series of Al⁺¹¹ in a laser-produced plasma shows population inversion between the n = 4,5 levels and the n =3 level at a plasma density N_e～10²⁰ cm^-3. The cooling of the expanding plasma leading to inversion is enhanced by a special target configuration. The gain coefficient in the 4 → 3 transition at 129.7 Å is estimated to be ～ 10 cm^-1, using both measured line intensities and numerical simulation.     

Stark broadening of lines from multiply-charged carbon ions in a high-density arc plasma

Profiles of C(III) and C(IV) lines emitted in the VUV and visible regions from a pulsed arc (N_e=1.5×10¹⁸ cm^-3, T_e=5.3×10⁴K) have been measured with time resolution. The experimental results are in satisfactory agreement with the predictions of electron impact theory for (3-3) and (3-4) transitions for which the energy separation between the upper level and the nearest perturbing level is smaller than the electron thermal energy. For lines from (2-2) transitions for which the plasma is optically thick, damping constants determined experimentally agree with theoretical values within a factor of two.     

Die Erzeugung von Seriengrenzkontinua mit Hilfe von Gleitfunken zur Absolutmessung im Vakuum-Ultraviolett

A lithium plasma is produced by discharging a 40 kV, 0,3 μF capacitor through a lithium-hydride-capillary (diameter 2 mm, length 20 mm) in vacuum (p～10^?4 Torr). During the first half-cycle (0,6 μs) Bremsstrahlung of Li III is observed in the visible and infrared, and the Lyman series of Li III together with the recombination continuum in the vacuum UV (100 Å). The high members of the Lyman series are broadened by Stark effect giving an electron density of about 6 · 10¹⁸ cm^?3. In the infrared the radiation is emitted from an optically thick plasma at a time when the free-free continuum in the visible is emitted from an optically thin plasma. Temporal development of electron temperatureT _e and electron density N_e has been measured from the absolute intensity in these spectral regions. Typical values ofT _e=230 000° K andN _e 5 · 10¹⁸ cm^?3 e.g. have been obtained. For these values the relaxation time for an ionisation equilibrium is short compared to the observation time. The complete ionisation of Li III has been checked by absorption measurements near 100 A. Thus the absolute intensity of the recombination continuum could be calculated. An experimental arrangement was built to measure simultaneously the time history of the intensity in the vacuum ultraviolet, in the visible, and infrared spectral regions.     

Numerical and analytical study of high-resolution limb spectral radiance from nonequilibrium atmospheres

Emission line shapes are calculated numerically for isolated optically thick infrared lines in the earthlimb as a function of tangent height using a general nonlocal thermodynamic equilibrium (non-LTE), upper-atmospheric line-by-line radiation transport code. It is shown that the exact integral form of the transport equation can be written in a form that is easily amenable to analytical approximation of high accuracy. In this form, the limb spectral radiance I_v appears as a weighted average of n_u/n_l, the ratio of upper-state to lower-state population density, multiplied by the absorptivity 1 - exp[-τ(v)], where τ(v) is the total optical path along the line of sight. In the wings the variation of I_v is governed by the absorptivity; in the core of the optically thick line, I_v is determined by the averaged population ratio. The analytical forms enable us to calculate all of the important features of the self-absorbed line and agree remarkably well with more time-intensive numerical calculation. These results are illustrated by calculations on the 15-μm CO₂v₂ (01¹0-00⁰0) vibrational transition for tangent heights ranging through the mesosphere and lower thermosphere. Even though the collision linewidth is less than 1% of the Doppler width at these altitudes, it is shown that it is essential to use the Voigt line profile in this calculation rather than the Doppler profile. Failure to do so leads to a total band radiance that is in error by up to a factor of three, as well as incorrect band shapes and line shapes.     

Population inversion between the ground and first excited states in a recombining hydrogen plasma

Plasma conditions for generating a population inversion between the ground and first excited states in a recombining hydrogen plasma have been investigated on the basis of the CR model. Population inversion can be expected when three-body recombination plays a dominant role; the required regions of electron density and temperature are specified. It is shown that upper bounds exist for the ground-state population density at given electron density and temperature. Larger inversion densities can be obtained between the ground and first excited states than between excited levels. Numerical results are presented.     

MgⅪ 1s3p-1s4p能级间平均高温及高密度条件下的粒子数反转

采用最新设计带侧向喷口的微管靶,当微管内壁平均激光辐照强度约为3.5×10¹³W·cm^-2时,观察到沿整个喷口1s3p ¹P₀⁰和1s4p ¹P₀⁰能级间强烈的粒子数反转。测得相应环境等离子体平均电子温度470—520eV,密度约为2×10²⁰cm^-3。分析了可能导致高温条件下粒子数反转的机制。 关键词：     

Density profiles in tokamaks from electron cyclotron radiation spectra

Measurement of the line shape of optically thick and optically thin lines in the electron cyclotron radiation spectrum emitted by a tokamak plasma may yield both electron temperature and density profiles. Currently temperature profiles are routinely extracted from optically thick lines. Consequently, this paper is addressed to the density profile problem. Algorithms for extracting density profiles are outlined in the case of uncontrolled reflection and controlled reflection of the cyclotron radiation within the tokamak vacuum chamber.     

Comparison of single and multiple scattering approaches for the simulation of limb-emission observations in the mid-IR

The validity of single scattering radiative transfer calculations for simulation of limb-emission measurements of clouds in the mid-infrared spectral region was investigated by comparison with a multiple scattering model. For in limb direction optically thin clouds, like polar stratospheric clouds, errors of the single scattering scheme range below 3%. For optically thick clouds deviations are below 3% in case of low single scattering albedo (ω₀=0.24) increasing up to 10-30% for ω₀=0.84. Clouds which are optically thick in limb, but thin in nadir direction, can cause limb radiances which are by a factor of 1.7 higher than the blackbody radiance at cloud altitude.     

Spectrum diagnostics. The necessity for detailed non-LTE modeling of X-ray emission from dense plasmas

Except in the simplest of physical situations, broadband spectrum formation in dense optically thick plasmas is the result of a highly complex set of nonlinear phenomena. At NRL, we are developing models to investigate a number of the theoretical issues related to the interpretation of time integrated X-ray spectra. Many of the individual features of these spectra can be understood qualitatively and modeled quantitatively (see Ref. 3). However, a number of questions concerning the self-consistency of theoretical treatments of an entire spectrum remain. A few of these questions will be examined and discussed in this talk within the context of imploding plasmas.Spectrum formation at high ion densities will be described using an argon K-shell model containing atomic structure up to n = 10 in both hydrogen and helium-like ionization stages as well as lower excited states in the lithium-like system. Lyman series emission is computed along with three prominent satellite lines of the H- and He-L_α lines and He 1s²?1s2p³P intercombination line. Local Stark profiles are also computed and used for L_α, L_β, and L_γ lines of both the hydrogen and helium-like series. For the higher lying lines, which are strongly overlapped at high densities, collisional width estimates for Voigt profiles are used. The overlap of satellite, intercombination, and L_α resonance lines, on the other hand, occurs as the result of overlapping Stark and Voigt profiles.The influence of these different line profile assumptions on spectrum formation at high density will be discussed in terms of the problems of self-consistently inferring plasma conditions during emission, such as temperature, density, and plasma ionization state. These are usually inhomogeneous in both space and time. However, some recent progress at NRL enables us to theoretically address these problems. We will discuss them within the context of post-processing the temperature and density profiles that are predicted by hydrodynamics calculations of imploded, Argon/DT filled, glass microballoons.     

High-pressure amplified stimulated emission effect in a N2 laser produced plasma with axicon lenses

An axicon is used to focus a CO₂-TEA laser pulse in a high pressure preionized mixture of He-N₂. An amplified stimulated emission (ASE) effect at 337.1 nm (N₂) is obtained. The dependence of inversion population on the electron density is shown. Also presented is the electron temperature as a function of the CO₂ pulse intensity for different mixtures of He-N₂.     

A non-equilibrium atmospheric pressure Capacitively-Coupled-Plasma (CCP) driven at VHF (162 MHz) for plasma catalysis of CO2 into CO

The design of a Very-High-Frequency (VHF) 162 MHz driven atmospheric-pressure Capacitively-Coupled-Plasma (CCP), with top and bottom electrodes operated in push-pull configuration, powered via a Power-Splitting-Transmission-Line-Driver (PSTLD), is presented. Application to the reprocessing of carbon dioxide into carbon-monoxide in this "high” VHF atmospheric plasma is presented, demonstrating some behaviour of the plasma source. rf power in the system is characterized using measured current (~ 1′s Amps peak) and voltage (~ 10′s Volts peak) waveforms at the electrode; Both are sinusoidal confirming a glow-discharge operational condition. Analysis of Optical Emission Spectra results find a highly non-equilibrium plasma, with high vibrational temperatures (from N₂) in the range ~4000 K, while gas temperature, monitored by a thermocouple at the gas outlet, remains low ~300 K, and confirmed by analysis of the N₂ rotational bands. The relative density of CO produced, as a by-product of CO₂ dissociation, is measured optically using N₂ as an actinometer. The CO density increases with rf power and longer gas residence times in the plasma volume. The high VHF atmospheric plasma is found to operate in pure CO₂ flows (no helium) with minimal gas heating for the full range of power densities (specific energy input of 0.4–2 eV per molecule) investigated.     

Measurement of atom and molecule number densities in hydrogen arcs by means of VUV spectroscopy

The number density of ground state atoms in the 2mm hydrogen arc (T≈20000 K) and the number density of molecules in the 5 mm hydrogen arc (T≈12000 K) have been measured by means of vuv spectroscopy. These species' are particularly likely to deviate from the equilibrium population and may therefore falsify the hydrogen transport coefficients measured in arc experiments. In the present investigation the optically thick line wings of Ly-α and the H₂ molecular spectrum around 1600 Å have been analyzed. The results demonstrate that the former assumptions of LTE and PLTE, respectively, are completely justified on and near the arc axis. However, in the outer zones of these arcs a considerable overpopulation of the molecules must be expected as a consequence of radial diffusion.     

Highly excited,normally inaccessible vibrational levels by sub-doppler modulated gain spectroscopy: The Na2 A1Σ+u state

Modulated gain spectroscopy is a sensitive, widely applicable, rovibronically state selective, sub-Doppler, triple resonance method for examining excited vibronic levels which are Franck—Condon inaccessible from thermally populated levels of the electronic ground state. A cw optically pumped molecular laser (OPL) prepares a steady-state population in a selected, vibrationally highly excited, rotation-vibration level of the electronic ground state (the lower level of the OPL transition). An intensity-modulated, single frequency dye laser excites part of this intracavity OPL-prepared population to the level of interest, thereby causing an increase in the OPL population inversion density, and, in turn, its output power. As the frequency of the dye laser is scanned, resonances are selectively detected by the appearance of modulation on the OPL output power; discrimination against dye laser excitations out of levels unconnected with the OPL is nearly perfect. Sub-Doppler (≈300 MHz FWHM) transitions are observed, thereby extending knowledge of the Na₂A¹Σ⁺_u state from v=44 to 62.     

“水窗”波段类氦Al离子2p-3dX射线激光的粒子数反转研究

报道类氦Al用离子2p—3d粒子数反转的理论与实验研究结果,实验中观测到ls2p—ls3p能级间的粒子数反转,详细研究了其反转系数与激光等离子体参数及靶结构的相互关系,并与理论计算结果进行了比较,得到了令人满意的结果。     

An investigation of the energy exchange mechanisms involving the 23S metastable level in an RF helium plasma

The energy exchange mechanisms present in a pure helium and a helium-neon plasma were investigated using spectroscopic diagnostic techniques. The plasma was spatially resolved and only the volume element at the plasma centerline was considered in the energy- exchange analysis. The experiment was conducted with a constant total pressure of 0·7 torr, a fixed oscillator frequency of 4 MHz, and a constant input power of 1·8 kW. Emission line spectroscopy was used to determine the population densities of 16 levels in the n³S, n³P, and n³D series. Spatially resolved, self-absorption measurements of the 2³P-2³S transition were used to determine the 2³S metastable level number density. The electron number density of 3·3 × 10¹³ cm^-3 was determined from the spatially resolved H_β blue wing profile, and a lower bound excitation temperature of 8800 °K was determined from a Boltzmann plot of the spatially resolved lower bound levels of the excited helium. The addition of 10% and 20% by volume of neon gas caused a measurable decrease in the population densities of the lower bound levels of helium, while the electron number density and lower bound excitation temperature remained unchanged. Three energy exchange models (local thermal equilibrium, corona, and collisional- radiative) were examined, and the collisional-radiative model was found to best describe the excitation processes for the 2³S level. This model was also appropriate for describing the helium-neon plasma at this level.     

Power determination and hydrino product characterization of ultra-low field ignition of hydrated silver shots

Hydrated silver shots comprising a source of H and HOH catalyst were ignited by passing a low voltage, high current through the shot to produce explosive plasma that emitted brilliant light predominantly in the short-wavelength 10 to 300 nm region. Based on Stark broadening, the initially optically thick essentially 100% ionized plasma expanded at sound speed or greater and thinned to emit EUV and UV light. The peak power of 20 MW was measured using absolute spectroscopy over the 22.8–647 nm region wherein the optical emission energy was 250 times the applied energy. Synchronized high-speed video and spectroscopic recording of the plasma emission and the measurement of the applied ignition power over time showed that plasma persisted even after the ignition power decayed to zero. Continuous megawatt-level power was recorded on a hydrino reactor wherein continuous brilliant plasma was maintained by HOH and H produced from water-entrained injected molten silver matrix. The molten fuel produced the same EUV spectrum as the shots, but converted to 5700 K blackbody radiation of about 1 m² surface area with a positive feedback cycle of silver vaporization and absorption of the hydrino reaction emission with the plasma becoming increasingly optically thick. The calorimetrically measured power of a typical 80 mg, 10 microliter shot ignition released by the nascent HOH catalyzed transition of H to hydrino state H₂ (1/4) was 400,000 W. Based on the shockwave propagation velocity and the corresponding pressure, the high-current ignition of water in a silver matrix was measured to produce a shock wave that was equivalent to about 10 times more moles of gunpowder. The catalysis reaction product H₂(1/4) was identified by Raman spectroscopy, photoluminescence emission spectroscopy, X-ray photoelectron spectroscopy, and MAS ¹H NMR.     

High quality weld of melt textured YBCO using Ag doped YBCO junctions

The addition of silver to YBa₂Cu₃O_7−δ (Y123) is well known to decrease its decomposition temperature. This study demonstrates the success in welding large Y123 textured samples with Ag doped Y123 junctions. Attempts to weld two melt textured domains of Y123 by a 1 mm thick layer of Ag doped Y123 are reported. The crucial importance of the initial Y211 excess content in the spacer material is pointed out. Microstructural observations, trapped field measurements and transport critical current density measurements prove that for a given Y211 amount a very high joint quality can be obtained. A transport critical current density as high as 10 kA/cm² is registered through the junction at 77 K and 5 T when the applied field is parallel to the (a,b) planes.