Secondary processes in proton auroras.
Direct ionization and secondary excitation in proton auroras, noting magnitude of contribution by various processes
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Results for “Ionization processes”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Energy branching in the Io plasma torus - The failure of neutral cloud theory
Model calculations are used to explore the energy source characteristics of the energy branching of the hot Io plasma torus. It is assumed that the energy is derived from the kinetic energy acquired by ions created in the rotating planetary magnetic field, and that Coulomb collisions with the electron gas control the flow of energy to the ionizing and radiative processes. The results show that neutral cloud theory is qualitatively inadequate. It is shown that neutral cloud theory can only support a dominantly singly ionized system (at the measured electron densities in the plasma torus) and that it fails to predict observed plasma properties relative to variations in number density.
Shemansky, D. E.↗
The ancient oxygen exosphere of Mars: Implications for atmosphere evolution
This study involves the calculation, by the 2-stream method of Nagy and Cravens, of 'hot' oxygen exosphere density profiles for 'ancient' atmospheres and ionospheres (e.g., different extreme ultraviolet fluxes) and the associated escaping fluxes. We computed the total production rates above different 'nominal' ionopause altitudes (not taking into account the fact that some will reenter the atmosphere). We do not consider the additional neutral escape due to the sputtering process described by Luhmann and Kozyra. The results presented here thus represent conservative estimations of the neutral escape fluxes, but generous estimates of ion loss rates (except that here we do not consider charge exchange and impact ionization ion production processes). Further work along the lines of Luhmann and Kozyra can lead to estimates of sputtering losses over time and the roles played by impact ionization and charge exchange.
Zhang, M. H. G.↗
Atic Experiment: Flight Data Processing
The Advanced Thin Ionization Calorimeter (ATIC) is a balloon borne experiment to measure the composition and energy spectra of Z = 1 to 28 cosmic rays over the energy range approx. 30 GeV - 100 TeV. The instrument consists of a fully active 320-crystal Bismuth Germanate (BGO) calorimeter, 202 scintillator strips in 3 hodoscopes interleaved with a graphite target, and a 4480-pixel silicon matrix charge detector. ATIC has had two successful Long Duration Balloon flights from McMurdo, Antarctica: from 12/28/00 to 01/13/01 and from 12/29/02 to 01/18/03. We have developed the ATIC Data Processing System (ADPs), which is an Object Oriented data processing program based on ROOT. In this paper, we describe the processing scheme used in handling the flight data, especially the calibration method and the event reconstruction algorithm.
Ahn, H. S.↗
Local shear instabilities in weakly ionized, weakly magnetized disks
We extend the analysis of axisymmetric magnetic shear instabilities from ideal magnetohydrodynamic (MHD) flows to weakly ionized plasmas with coupling between ions and neutrals caused by collisions, ionization, and recombination. As part of the analysis, we derive the single-fluid MHD dispersion relation without invoking the Boussinesq approximation. This work expands the range of applications of these instabilities from fully ionized accretion disks to molecular disks in galaxies and, with somewhat more uncertainty, to protostellar disks. Instability generally requires the angular velocity to decrease outward, the magnetic field strengths to be subthermal, and the ions and neutrals to be sufficiently well coupled. If ionization and recombination processes can be neglected on an orbital timescale, adequate coupling is achieved when the collision frequency of a given neutral with the ions exceeds the local epicyclic freqency. When ionization equilibrium is maintained on an orbital timescale, a new feature is present in the disk dynamics: in contrast to a single-fluid system, subthermal azimuthal fields can affect the axisymmetric stability of weakly ionized two-fluid systems. We discuss the underlying causes for this behavior. Azimuthal fields tend to be stabilizing under these circumstances, and good coupling between the neutrals and ions requires the collision frequency to exceed the epicyclic frequency by a potentially large secant factor related to the magnetic field geometry. When the instability is present, subthermal azimuthal fields may also reduce the growth rate unless the collision frequency is high, but this is important only if the field strengths are very subthermal and/or the azimuthal field is the dominant field component. We briefly discuss our results in the context of the Galactic center circumnuclear disk, and suggest that the shear instability might be present there, and be responsible for the observed turbulent motions.
Blaes, Omer M.↗
The influence of autoionization accompanied by excitation on dielectronic recombination and ionization equilibrium
In the process of dielectronic recombination, the doubly excited state formed by radiationless capture may autoionize preferentially into an excited state of the recombining ion. This additional autoionization process has not been discussed in previous treatments of dielectronic recombination. The dielectronic recombination rates for certain nonhydrogenic Fe ions, although still larger than the direct radiative recombination rates, are found to be substantially reduced by the inclusion of the additional autoionization rate in the branching ratio for the stabilizing radiative transition. Consequently, the temperatures of maximum equilibrium abundance are significantly lower than those predicted by recent calculations. Finally, the radiative energy loss rate coefficients are calculated for radiation processes involving electron Fe-ion collisions in high-temperature plasmas. Electron impact excitation of resonance line radiation is the dominant radiative cooling mechanism in steady-state plasmas at temperatures where ions with bound electrons are abundant. However, it is found that the radiation emitted during dielectronic recombination can be more important than direct recombination radiation and bremsstrahlung.
Jacobs, V. L.↗
All Ionospheres are not Alike: Reports from other Planets
Our understanding of planetary ionospheres made some progress during the last four years. Most of this progress was due to new and/or improved theoretical models, although some new data were also obtained by direct and remote sensing observations. The very basic processes such as ionization, chemical transformations and diffusive as well as convective transports are analogous in all ionospheres; the major differences are the result of factors such as different neutral atmospheres, intrinsic magnetic field strength, distance from the Sun, etc. Improving our understanding of any of the ionospheres in our solar system helps in elucidating the controlling physical and chemical processes in all of them. New measurements are needed to provide new impetus, as well as guidance, in advancing our understanding and we look forward to such information in the years ahead.
Nagy, Andrew F.↗
Damage to cellular DNA from particulate radiations, the efficacy of its processing and the radiosensitivity of mammalian cells. Emphasis on DNA double strand breaks and chromatin breaks
For several years, it has been evident that cellular radiation biology is in a necessary period of consolidation and transition (Lett 1987, 1990; Lett et al. 1986, 1987). Both changes are moving apace, and have been stimulated by studies with heavy charged particles. From the standpoint of radiation chemistry, there is now a consensus of opinion that the DNA hydration shell must be distinguished from bulk water in the cell nucleus and treated as an integral part of DNA (chromatin) (Lett 1987). Concomitantly, sentiment is strengthening for the abandonment of the classical notions of "direct" and "indirect" action (Fielden and O'Neill 1991; O'Neill 1991; O'Neill et al. 1991; Schulte-Frohlinde and Bothe 1991 and references therein). A layer of water molecules outside, or in the outer edge of, the DNA (chromatin) hydration shell influences cellular radiosensitivity in ways not fully understood. Charge and energy transfer processes facilitated by, or involving, DNA hydration must be considered in rigorous theories of radiation action on cells. The induction and processing of double stand breaks (DSBs) in DNA (chromatin) seem to be the predominant determinants of the radiotoxicity of normally radioresistant mammalian cells, the survival curves of which reflect the patterns of damage induced and the damage present after processing ceases, and can be modelled in formal terms by the use of reaction (enzyme) kinetics. Incongruities such as sublethal damage are neither scientifically sound nor relevant to cellular radiation biology (Calkins 1991; Lett 1990; Lett et al. 1987a). Increases in linear energy transfer (LET infinity) up to 100-200 keV micron-1 cause increases in the extents of neighboring chemical and physical damage in DNA denoted by the general term DSB. Those changes are accompanied by decreasing abilities of cells normally radioresistant to sparsely ionizing radiations to process DSBs in DNA and chromatin and to recover from radiation exposure, so they make significant contributions to the relative biological effectiveness (RBE) of a given radiation.(ABSTRACT TRUNCATED AT 400 WORDS).
Non-NASA Center↗
The cosmic dust analyzer: Experimental evaluation of an impact ionization model
A thermal equilibrium plasma model is used to process data from an impact ionization time-of-flight mass spectrometer in order to convert the raw ion data to relative abundances of the elemental constituents of cosmic dust particles.
Friichtenicht, J. F.↗
Shock ionization kinetics of pure nitrogen.
Ionization rate limiting processes behind strong shock waves in pure N, plotting electron density profile diagrams
Bentley, S. B.↗
Ion implantation reduces radiation sensitivity of metal oxide silicon /MOS/ devices
Implanting nitrogen ions improves hardening of silicon oxides 30 percent to 60 percent against ionizing radiation effects. Process reduces sensitivity, but retains stability normally shown by interfaces between silicon and thermally grown oxides.
Source record↗
Atomic and molecular studies
The collisions of heavy particles were studied to increase the understanding of the collision of meteoroids with the upper atmosphere. The various methods applied to the development of theoretical models for determining collision processes responsible for ionization and excitation in the meteor collision are discussed.
Flannery, M. R.↗
Wave propagation in a quasi-chemical equilibrium plasma
Wave propagation in a quasi-chemical equilibrium plasma is studied. The plasma is infinite and without external fields. The chemical reactions are assumed to result from the ionization and recombination processes. When the gas is near equilibrium, the dominant role describing the evolution of a reacting plasma is played by the global conservation equations. These equations are first derived and then used to study the small amplitude wave motion for a near-equilibrium situation. Nontrivial damping effects have been obtained by including the conduction current terms.
Fang, T.-M.↗
Bit-error rates in optical communications
Statistical model, which consists of on/off binary system, assumes Poisson detection process and log-normal atmospheric scintillation. Based upon detection process and atmospheric ionization, piecewise linear model for adaptive threshold system is developed.
Webb, W. E.↗
Energy loss by resonance line photons in an absorbing medium
The mean path length of photons undergoing repeated scatterings in media of large optical thickness is calculated from accurate numerical solutions of the transfer equation including the effect of frequency redistribution characteristic of combined Doppler and natural broadening. Energy loss by continuous absorption processes, such as ionization or dust absorption, is discussed, and asymptotic scaling laws for the energy loss, the mean path length, and the mean number of scatterings are inferred from the numerical data.
Hummer, D. G.↗
Requirements for theoretical models of outflows
Recent observational and theoretical investigations of astrophysical mass outflows are reviewed, with a focus on the basic physical principles. Specific limitations on the observational data and their interpretation are listed and discussed. Modeling problems considered include the role of the critical point in determining the mass-loss rate and terminal velocity, the physical processes controlling density at the critical point, the possible coexistence of multiple mass-loss mechanisms, time scales, instabilities and phase changes, multiphase atmospheres and winds, the definition of geometries, the role of the environment, explosive transient events, stochastic phenomena, mode-mode coupling and damping processes, departures from ionization equilibrium, and nonthermal phenomena.
Linsky, Jeffrey L.↗
A new class of solutions for interstellar magnetohydrodynamic shock waves
An analysis is presented of the equations of motion for steady MHD shock waves proopagating in interstellar clouds, for boundary conditions that preclude C shocks. In addition to J shocks, in which the neutral fluid component becomes subsonic at an adiabatic jump front, the equations admit a new class of solutions, called C-asterisk shocks, in which the transition to subsonic flow occurs continuously at a sonic point. Numerical methods are developed for computing the structure of J and C-asterisk shocks propagating in diffuse interstellar clouds. The effects of chemical, ionization, and recombination processes are included in this treatment. An alternative numerical method, which uses artificial viscosity to facilitate integration through sonic points, is analyzed and shown to be invalid. A set of exemplary solutions, computed for realistic shock parameters, shows that C-asterisk shocks occur for a broad range of conditions relevant to diffuse interstellar clouds.
Roberge, W. G.↗