Autoionization effects in ultraviolet absorption spectra of hot gases Scientific report no. 6
Autoionization effects in ultraviolet absorption spectra of hot gases
ULTRAVIOLET SPECTROSCOPY↗
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Determination of C1-C4 alkanes by ion mobility spectrometry
Results are presented from a comparison between two ion-mobility-spectrometer (IMS) methods of sample ionisation: a conventional IMS with very dry helium and an IMS using metastable helium ionization. As one of the tests, a mixture of several hydrocarbons expected to be the components of Titan's atmosphere (made of ethane, ethylene, acetylene, propane, n-butane, isobutane, and propyne in concentrations from 20 to 200 ppm) was analyzed by both methods. Results from the dry-He IMS showed that the dry-helium approach was more adequate for the analysis of these gases than the metastable-helium IMS approach. In the metastable-He approach, in which several versions of He ionization reaction were tested, the spectra produced were not as clear as the conventional IMS spectra, due to the fact that the strong electric field introduced in the reaction region to generate metastable helium affected the gating, resolution, and collection of the ions.
Kojiro, Daniel R.↗
Balloon-borne photoionization mass spectrometer for measurement of stratospheric gases
A balloon-borne photoionization mass spectrometer used to measure stratospheric trace gases is described. Ions are created with photons from high-intensity krypton discharge lamps and a quadrupole mass analyzer is employed for ion identification. Differential pumping is achieved with liquid helium cryopumping. To insure measurement of unperturbed stratospheric air, the entire system is contained in a sealed gondola and the atmospheric sample is taken some distance away during descent. The photoionization technique allows the detection of a low ionization potential constituent, such as nitric oxide, at less than a part in one billion in the presence of the major atmospheric gases and their isotopes. Operation of the mass spectrometer system was demonstrated during a daytime flight from Palestine, Texas on 26 April 1977. The sensitivity achieved and the unique selectivity afforded by this technique offer a capability for trace constituent measurement not possible with the more conventional electron impact ionization approach.
Aikin, A. C.↗
Reverse Energy Cascade in Turbulent Weakly Ionized Plasmas
For systems far from equilibrium, the neglect of a role for viscous effects in turbulence may be generally inappropriate when the relaxation time for the molecular process approaches the local flow time (Orou et al. (1996)). Furthermore, for stationary collisional plasmas, the conventional Reynolds number is irrelevant under circumstances where the standard features of turbulence in ordinary gases are observed in the plasma (Johnson et al. (1987)). The current theoretical understanding of these turbulent phenomenon is particularly inadequate for turbulence associated with ionizing shock waves; generally speaking, thermodynamic, acoustic and pressure fluctuations are all seen as amplified across the shock wave followed by a dramatic decay (relaminarization) usually attributed to a lack of importance of viscosity in the turbulent regions. This decay would be accelerated when the flow speed is also reduced due to the importance usually given to the conventional Reynolds number (which is directly proportional to velocity) as a quality of turbulence index. However, evidence supporting this consensus is lacking. By contrast, recent evidence of vanishing triple correlations form De Silva et al. (1996) provides strong support for early theoretical speculation of inherently molecular effects in macroscopic turbulence in Tsuge (1974). This specifically suggests that the role of compressive effects ordinarily associated with the shock wave could be significantly muted by the existence of a strongly turbulent local environment. There is also more recent theoretical speculation (Frisch et al. (1984)) of an inherently and previously unsuspected non-dissipative nature to turbulence, with energy conservation being nurtured by reverse energy cascades in the turbulent fluctuation spectra. Furthermore, the role which might be played by fluctuations on quantum mechanical phenomena and variations in molecular parameters is completely unknown, especially of the sort which might be found in optical spectra. A determination of the role which changing turbulent parameters might play on optical signatures behind a reflected shock wave should therefore provide a useful tool for the evolution of theoretical models for turbulence.
Williams, Kyron↗
Soft X-ray opacity in hot and photoionized gases
New calculations are presented of the soft X-ray opacity of gas having cosmic elemental abundances, but in a variety of ionization states. Coronal ionization equilibrium is considered over the range of temperatures 10 to the 4th to 3 x 10 to the 8th K and photoionization equilibrium with power-law and thermal bremsstrahlung spectra over a wide range of ionization parameters. The results are displayed in illustrative figures. For temperatures and ionization parameters commonly found in astrophysical plasmas, the opacity (particularly to photons of equal to or less than 1 keV) can be diminished by substantial factors relative to the state in which all atoms are neutral. As the dominant ionization stages change, the positions and contrasts of prominent K-edges also change.
Krolik, J. H.↗
High-resolution emission-line imaging of Seyfert galaxies. I - Observations. II - Evidence for anisotropic ionizing radiation
A CCD direct imaging survey of 11 Seyfert galaxies with a mean seeing of 1.3 arcsec FWHM is presented. It is found that the major axes and spatial scales of the circumnuclear emission-line gas are very similar to those of the radio continuum sources. In the second part, this close connection between thermal and relativistic gases is examined. A scenario is proposed in which the radio jets and plasmoids shock, accelerate, and compress ambient and entrained gas, with the dominant source of ionization being the nonstellar nuclear UV continuum.
Haniff, Christopher A.↗
The evolving intergalactic medium - The uncollapsed baryon fraction in a cold dark matter universe
The time-varying density of the intergalactic medium (IGM) is calculated by coupling detailed numerical calculations of the thermal and ionization balance and radiative transfer in a uniform IGM of H and He to the linearized equations for the growth of density fluctuations in both gases and a dark component in a cold dark matter universe. The IGM density is identified with the collapsed baryon fraction. It is found that even if the IGM is never reheated, a significant fraction of the baryons remain uncollapsed at redshifts of four. If instead the collapsed fraction releases enough ionizing radiation or thermal energy to reionize the IGM by z greater than four as required by the Gunn-Peterson (GP) constraint, the uncollapsed fraction at z of four is even higher. The known quasar distribution is insufficient to supply the ionizing radiation necessary to satisfy the GP constraint in this case and, if stars are instead responsible, a substantial metallicity must have been produced by z of four.
Shapiro, Paul R.↗
Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) Model - An Unified Concept for Earthquake Precursors Validation
The paper presents a conception of complex multidisciplinary approach to the problem of clarification the nature of short-term earthquake precursors observed in atmosphere, atmospheric electricity and in ionosphere and magnetosphere. Our approach is based on the most fundamental principles of tectonics giving understanding that earthquake is an ultimate result of relative movement of tectonic plates and blocks of different sizes. Different kind of gases: methane, helium, hydrogen, and carbon dioxide leaking from the crust can serve as carrier gases for radon including underwater seismically active faults. Radon action on atmospheric gases is similar to the cosmic rays effects in upper layers of atmosphere: it is the air ionization and formation by ions the nucleus of water condensation. Condensation of water vapor is accompanied by the latent heat exhalation is the main cause for observing atmospheric thermal anomalies. Formation of large ion clusters changes the conductivity of boundary layer of atmosphere and parameters of the global electric circuit over the active tectonic faults. Variations of atmospheric electricity are the main source of ionospheric anomalies over seismically active areas. Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) model can explain most of these events as a synergy between different ground surface, atmosphere and ionosphere processes and anomalous variations which are usually named as short-term earthquake precursors. A newly developed approach of Interdisciplinary Space-Terrestrial Framework (ISTF) can provide also a verification of these precursory processes in seismically active regions. The main outcome of this paper is the unified concept for systematic validation of different types of earthquake precursors united by physical basis in one common theory.
Pulinets, S.↗
Device and method for improving specific energy requirement of plasma pyrolyzing or reforming systems
Devices and methods for reducing the specific energy required to reform or pyrolyze reactants in plasmas operating at high flow rates and high pressures are presented. These systems and methods include 1) introducing electrons and/or easily ionized materials to a plasma reactor, 2) increasing turbulence and swirl velocity of the flows of feed gases to have improved mixing in a plasma reactor, and 3) reducing slippage from a plasma reactor system. Such plasma systems may allow plasma reactors to operate at lower temperatures, higher pressure, with improved plasma ignition, increased throughput and improved energy efficiency. In preferred embodiments, the plasma reactors are used to produce hydrogen and carbon monoxide, hydrogen and carbon, or carbon monoxide through reforming and pyrolysis reactions. Preferred feedstocks include methane, carbon dioxide, and other hydrocarbons.
Bromberg, Leslie↗
Laser Ablation Plasmas and Spectroscopy for Nuclear Applications
The development of measurement methodologies to detect and monitor nuclear-relevant materials remains a consistent and significant interest across the nuclear energy, nonproliferation, safeguards, and forensics communities. Optical spectroscopy of laser-produced plasmas is becoming an increasingly popular diagnostic technique to measure radiological and nuclear materials in the field without sample preparation, where current capabilities encompass the standoff, isotopically resolved and phase-identifiable (e.g., UO and UO[Formula: see text]) detection of elements across the periodic table. These methods rely on the process of laser ablation (LA), where a high-powered pulsed laser is used to excite a sample (solid, liquid, or gas) into a luminous microplasma that rapidly undergoes de-excitation through the emission of electromagnetic radiation, which serves as a spectroscopic fingerprint for that sample. This review focuses on LA plasmas and spectroscopy for nuclear applications, covering topics from the wide-area environmental sampling and atmospheric sensing of radionuclides to recent implementations of multivariate machine learning methods that work to enable the real-time analysis of spectrochemical measurements with an emphasis on fundamental research and development activities over the past two decades. Background on the physical breakdown mechanisms and interactions of matter with nanosecond and ultrafast laser pulses that lead to the generation of laser-produced microplasmas is provided, followed by a description of the transient spatiotemporal plasma conditions that control the behavior of spectroscopic signatures recorded by analytical methods in atomic and molecular spectroscopy. High-temperature chemical and thermodynamic processes governing reactive LA plasmas are also examined alongside investigations into the condensation pathways of the plasma, which are believed to serve as chemical surrogates for fallout particles formed in nuclear fireballs. Laser-supported absorption waves and laser-induced shockwaves that accompany LA plasmas are also discussed, which could provide insights into atmospheric ionization phenomena from strong shocks following nuclear detonations. Furthermore, the standoff detection of trace radioactive aerosols and fission gases is reviewed in the context of monitoring atmospheric radiation plumes and off-gas streams of molten salt reactors. Finally, concluding remarks will present future outlooks on the role of LA plasma spectroscopy in the nuclear community.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
SiPM-matrix readout of two-phase argon detectors using electroluminescence in the visible and near infrared range
Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter searches to record (in the gas phase) the ionization signal induced by particle scattering in the liquid phase. The “standard” EL mechanism is considered to be due to noble gas excimer emission in the vacuum ultraviolet (VUV). In addition, there are two alternative mechanisms, producing light in the visible and near infrared (NIR) ranges. The first is due to bremsstrahlung of electrons scattered on neutral atoms (“neutral bremsstrahlung”, NBrS). The second, responsible for electron avalanche scintillation in the NIR at higher electric fields, is due to transitions between excited atomic states. In this work, we have for the first time demonstrated two alternative techniques of the optical readout of two-phase argon detectors, in the visible and NIR range, using a silicon photomultiplier matrix and electroluminescence due to either neutral bremsstrahlung or avalanche scintillation. The amplitude yield and position resolution were measured for these readout techniques, which allowed to assess the detection threshold for electron and nuclear recoils in two-phase argon detectors for dark matter searches. To the best of our knowledge, this is the first practical application of the NBrS effect in detection science.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Ionizing potential waves and high-voltage breakdown streamers.
The structure of ionizing potential waves driven by a strong electric field in a dense gas is discussed. Negative breakdown waves are found to propagate with a velocity proportional to the electric field normal to the wavefront. This causes a curved ionizing potential wavefront to focus down into a filamentary structure, and may provide the reason why breakdown in dense gases propagates in the form of a narrow leader streamer instead of a broad wavefront.
Albright, N. W.↗
Generation of ultraviolet and vacuum ultraviolet radiation
The paper describes nonlinear optical techniques that use phase-matched mixtures of metal vapors and inert gases, or, in certain cases, only inert gases for the generation of ultraviolet radiation. These systems are transparent where nonlinear crystals are opaque and their high ionization permits optical power densities of 10 to the 10 or 10 to the 11 W/sq cm to be utilized. An experiment designed to convert incident 1.064 micron radiation to 3547 A radiation is described as are experiments designed to generate vacuum ultraviolet at 1773, 1520, 1182 and 887 A. Theoretical considerations on the use of this nonlinear optical technique for the generation of soft X-rays are presented and the construction of a vacuum ultraviolet holographic grating with a fringe spacing of 836 A is reported on.
Harris, S. E.↗
On the energy resolution obtained with a multistep proportional counter
Results of laboratory experiments with a standard multiwire imaging proportional counter (MWPC), modified to include a parallel grid preamplification stage are presented. Both argon and xenon were used as the primary absorbing gas in conjunction with a number of quench gases. It is found that extremely good energy resolution is obtained from the preamplification stage, almost independent of the ionization potential of the quench gas and over a broad range of gains. Furthermore, regardless of absorbing gas or quench agent, there was no difficulty in transferring a portion of this preamplified charge to the MWPC section for multistep mode operation. Finally, even for overall system gains greater than 10,000, the energy resolution from the second stage is found to be significantly improved, as long as the preamplification stage is operating. These results should have wide application and are of special interest for X-ray astronomy.
Ramsey, B. D.↗
Volcanic control of the Io atmosphere and neutral and plasma torus
Rate equations for the column density of Io's atmosphere and the number density of neutral atoms and ions in the torus have been formulated in terms of surface sublimation and venting of volcanic gases, sputtering efficiency, thermal escape, and the plasma processes that take place in the torus which included electron impact ionization, charge exchange, and transport. In the limit of low volcanic activity, estimates of the densities can be obtained, and the baseline configuration that would exist in the absence of volcanic activity is found. Solution of the coupled steady state rate equations shows that the densities are sensitive, to a varying degree, to the level of Io volcanism. The steady state densities predicted by the model are consistent with a volcanic flux of no more than 10 to the 12th/sq cm per sec. This is significantly lower than the values obtained on the basis of resurfacing rates and appears to imply that surface lava flows play a major role in the resurfacing process.
Eviatar, Aharon↗
Numerical methods for TVD transport and coupled relaxing processes in gases and plasmas
The construction of second-order upwind schemes for nonequilibrium plasmas, for both one- and two-fluid formulations is demonstrated. Coupled relaxation processes, including ionization kinetics and radiative processes and their algorithms for nonequilibrium, multiple temperature conditions are described as well. The paper applies the numerical techniques on some simple test cases, points out critical problems and their solutions, and makes qualitative comparisons with known results, whenever possible.
Cambier, Jean-Luc↗
Space Shuttle's orbital environment
Variations with the solar cycle of chemical composition, density and temperature of the orbital environment of the Space Shuttle are reviewed; micrometeoroid fluxes, ionizing radiation, photon fluxes and cosmic ray bombardment to which the Shuttle will be subjected are also mentioned. In addition, gases arising from offgassing and outgassing of contaminants (at about 300 K) from the Shuttle are considered, and particulates ejected during rocket firings or from the leakage of pressurized vessels (i.e., the cabin) are taken into account.
Witteborn, F. C.↗
Extreme Speeds and Thermodynamic States in Supersonic Flight
The increasing importance of high-speed flow leads to similar problems in various fields of research which are summarized in what follows. Typical of all cases is the conversion of high kinetic energy into extreme thermodynamic states with temperatures of several thousand degrees, frequently connected with dissociation and ionization of the gas involved. There is also a characteristic small sensitivity to the processes discussed in the case of gases of low molecular weight (light gases). The penetration of meteors into the atmosphere of the earth at astronomical speeds results in temperatures higher than those of the surface of the sun. Such temperatures may be produced in shock tubes, with light gases used as the driving gas. For supersonic fighters the problem of propulsion is less difficult to solve than the problem of large heating, on the surface and in the combustion chamber. Finally, for the space-travel rocket, astronomical speeds have to be reached which require the lightest possible gases as propellants. Here again, dissociation processes in the combustion chamber are of considerable importance.
Oswatitsch, Klaus↗