Neutral flow interaction with a magnetic dipole plasma II. Global model
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Charles L. Kelly↗
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A discrete model of matter in the problem of rarefied plasma flowing past solids <diskretnaya model' veshchestva v zadache obtekaniya tel razrezhennoy plazmoy<
Self-consistent electric potential around axisymmetric body in stationary flow of rarefied plasma
SELF-CONSISTENT FIELD /SCF/↗
Mean excitation energies for stopping powers in various materials using local plasma oscillator strengths
The basic model of Lindhard and Scharff, known as the local plasma model, is used to study the effects on stopping power of the chemical and physical state of the medium. Unlike previous work with the local plasma model, in which individual electron shifts in the plasma frequency were estimated empirically, he Pines correction derived for a degenerate Fermi gas is shown herein to provide a reasonable estimate, even on the atomic scale. Thus, the model is moved to a complete theoretical base requiring no empirical adjustments, as characteristic of past applications. The principal remaining error is in the overestimation of the low-energy absorption properties that are characteristic of the plasma model in the region of the atomic discrete spectrum, although higher-energy phenomena are accurately represented, and even excitation-to-ionization ratios are given to fair accuracy. Mean excitation energies for covalent-bonded gases and solids, for ionic gases and crystals, and for metals are calculated using first-order models of the bonded states.
Wilson, J. W.↗
Time-dependent collisional-radiative model for capillary discharge plasmas
A time-dependent, zero-dimensional collisional-radiative model has been developed to study capillary discharge plasmas in view of possibilities for obtaining population inversion leading to laser action in the extreme ultraviolet and soft x-ray spectral region, by amplifying the Balmer-alpha (H-alpha) line of different hydrogenlike ions with nuclear charges from Z = 3 to Z = 6. The model is described in detail, and results for the case of a carbon plasma are presented. Limitations of the model are discussed and comparison is made between our calculations and recent experimental results.
Pockl, M.↗
Production of hard X rays in a plasma focus
A model of a plasma focus is examined wherein large axial electric fields are produced by an imploding current sheet during the final nanoseconds of the collapse phase and where the fields provide a mechanism for creating a beam of electrons of highly suprathermal energies. The expected bremsstrahlung radiation above 100 keV is calculated for such a beam, which has a power-law spectrum, both from electron-deuteron collisions in the focused plasma and when the beam reaches the wall of the device. It is concluded that, since the experimental results indicate little or no radiation above 100 keV originating in the walls, that the electrons in the beam must be decelerated after leaving the plasma and before reaching the wall. Comparisons with the results and the total energy of the device yield qualitative agreement with the expected angular distribution of hard X-rays and reasonable agreement with the total energy in accelerated electrons required to produce the observed total energy in hard X-rays by this mechanism.
Newman, C. E.↗
Twenty-seven day deviations of the interplanetary magnetic field and plasmas from the Parker spiral model
Interplanetary magnetic field and plasma structure observed with Mariners magnetometer, noting 27-day deviations from Parker spiral model
Rosenberg, R. L.↗
On the apparent diamagnetism of the lunar environment in the geomagnetic tail lobes
The reported investigation presents the magnetic observations averaged in a format that facilitates comparison with models of plasma diamagnetic effects. These models demonstrate that a decreased plasma energy density in the lunar vicinity always causes an induced dipole that increases the external field. Hence, an increased plasma energy density in the lunar environs is required to account for the observed magnetic decrease. There are several different plasma populations in the high-latitude geomagnetic tail lobes, including the lunar ions resulting from photoionization of lunar atmosphere neutrals, possible fluxes of polar-wind protons, low-energy particle events which consist of antisolar directed fluxes of 100-eV protons, photoelectrons from the dayside lunar surface, and a high-energy thermal population.
Goldstein, B. E.↗
Analytical model for the density distribution in the Io plasma torus
An analytical model is developed for the diffusive equilibrium plasma density distribution in the Io plasma torus. The model has been employed successfully to follow the ray path of plasma waves in the multi-ion Jovian magnetosphere; it would also be valuable for other studies of the Io torus that require a smooth and continuous description of the plasma density and its gradients. Validity of the analytical treatment requires that the temperature of thermal electrons be much lower than the ion temperature and that superthermal electrons be much less abundant than the thermal electrons; these two conditions are satisfied in the warm outer region of the Io torus from L = 6 to L = 10. The analytical solutions agree well with exact numerical calculations for the most dense portion of the Io torus within 30 deg of the equator.
Mei, YI↗
Structure of field rotating disturbances in warm plasma
A model in which thermal effects are simulated through use of a multibeam plasma distribution function is developed and investigated to see if solutions which take an initially uniform magnetized plasma to a new uniform state with different field orientation are possible. The momentum conservation integrals are found to admit two classes of such solutions, but only one class exhibits appropriate asymptotic behavior. Extensive numerical integrations have failed to demonstrate the existence of the desired solutions.
Wolfson, R.↗
Behavior of Triple Langmuir Probes in Non-Equilibrium Plasmas
A model of current collection in Langmuir probes is used to investigate the effect representative non- equilibrium plasmas under various conditions have on the electron temperature and number density that would be calculated through analysis of the probe collection characteristics. The model uses the distribution function to calculate the charged particle flux to a probe and then, for fixed applied voltages, the current values that satisfy continuity in the probes are determined. The triple probe is not scanned in voltage, so there is no practical way using experimental triple probe data to determine if the plasma is in equilibrium. As a consequence, a triple probe analysis typically relies on the assumption that the plasma is in equilibrium. Proceeding from this point, the numerically-generated non-equilibrium triple probe data are analyzed assuming that the plasma is in equilibrium, with the data compared to the initial distribution function inputs of plasma temperature and number density to determine the effect the non-equilibrium distribution has on plasma measurements. The temperature and number density are both significantly affected when a fraction of the particles in the distribution are shifted from the equilibrium configuration into the non-equilibrium part of the distribution function. For all instances studied, the computed electron temperature and number density are extremely sensitive to small deviations from equilibrium ( ≤ 5% of the plasma shifted into the non-equilibrium function). Shifting more of the plasma into the non-equilibrium distribution beyond this initial level does not produce a significant additional shift in the computed plasma properties.
Polzin, Kurt A.↗
A two-dimensional particle-in-cell model of a dusty plasma
Dusty plasmas are present in comets, in the ring systems of the outer planets, and in the interstellar medium. A two-dimensional particle-in-cell (PIC) model of a dusty plasma is presented in this paper. The PIC code is best suited for modeling the plasma-dust interaction for large grains, with diameters of the order of a centimeter. We have modeled the charging process for an individual dust grain and the associated potential pattern in the surrounding plasma. We have also considered the case of a large number of grains in a plasma, with intergrain separations of the order of the Debye length, and have shown that the plasma becomes depleted and the charge on a dust grain is reduced, as other workers in this field have predicted (cf. C. K. Goertz, 1989). We examine the electron and ion distribution functions in the vicinity of a charged grain and demonstrate that the ions near a grain have clearly been accelerated by the electrostatic potential.
Young, B.↗
Effects of magnetospheric electrons on polar plasma outflow - A semikinetic model
The effect or hot magnetospheric electrons on the polar-plasma outflow was investigated, using a semikinetic model developed by Wilson et al. (1990) and Ho et al. (1991) to simulate the effect. The model is based on a hybrid particle-in-cell approach, in which the H(+) and O(+) ions are treated as adiabatic parallel-drifting gyrocenters injected as the upgoing portions of drifting bi-Maxwellian distributions at 1.6 R(E), while the electrons are treated as a massless neutralizing fluid. The results show that, in order to simulate the polar outflow under the influence of hot magnetospheric electrons, it is necessary to consider the effect of the electron temperature gradient.
Ho, C. W.↗
The cooling and condensation of flare coronal plasma
A model is investigated for the decay of flare heated coronal loops in which rapid radiative cooling at the loop base creates strong pressure gradients which, in turn, generate large (supersonic) downward flows. The important features of this model which distinguish it from previous models of flare cooling are: (1) Most of the thermal energy of the coronal plasma may be lost by mass motion rather than by conduction or coronal radiation. (2) Flare loops are not isobaric during their decay phase, and large downward velocities are present near the footpoints. (3) The differential emission measure has a strong temperature dependence. These results can account for recent observations of compact flare loops that are not consistent with the previous cooling models.
Antiochos, S. K.↗
The cooling and condensation of flare coronal plasma
A model is investigated for the decay of flare heated coronal loops in which rapid radiative cooling at the loop base creates strong pressure gradients which, in turn, generate large (supersonic) downward flows. The coronal material cools and 'condenses' onto the flare chromosphere. The features which distinguish this model from previous models of flare cooling are: (1) most of the thermal energy of the coronal plasma may be lost by mass motion rather than by conduction or coronal radiation; (2) flare loops are not isobaric during their decay phase, and large downward velocities are present near the footpoints; (3) the differential emission measure q has a strong temperature dependence.
Antiochos, S. K.↗
High-Energy Electron-Ion and Photon-Ion Collisions: Status and Challenges
Non-LTE plasmas are ubiquitous in objects studied in the UV and X-ray energy bands. Collisional and photoionization cross sections for atoms and ions are fundamental to our ability to model such plasmas. Modeling is key in the X-ray band, where detector properties and limited spectral resolution limit the ability to measure model-independent line strengths, or other spectral features. Much of the motivation for studying such collisions and many of the tools, are not new. However, the motivation for such studies and their applications, have been affected by the advent of X-ray spectroscopy with the gratings on Chandra and XMM-Newton. In this talk I will review this motivation and describe the tools currently in use for such studies. I will also describe some current unresolved problems and the likely future needs for such data.
Kallman, Timothy R.↗
The Darwin model as a tool for electromagnetic plasma simulation
The Darwin model of electromagnetic interaction is presented as a self-consistent theory, and is shown to be an excellent approximation to the Maxwell theory for slow electromagnetic waves. Since the fast waves of the Maxwell theory are absent, it is convenient for use in the computer simulation of the electromagnetic dynamics of nonrelativistic plasma.
Kaufman, A. N.↗
Modeling of the geosynchronous plasma environment
An analytic simulation of the geosynchronous environment in terms of local time and the daily A sub P index is presented. The simulation is compared with actual statistical data from approximately 50 days of ATS 5 plasma data and 50 days of ATS 6 plasma data. At low levels of activity the model adequately simulates the local time variations of the plasma parameters. At high values of geomagnetic activity, the predicted magnitudes of the plasma parameters agree with the statistical results but the effects of multiple injections are evident in both the data and the simulation, biasing the local time variations.
Garrett, H. B.↗
A model of the Io plasma ribbon
The plasma ribbon noted by Trauger's (1984) in earth-based measurements of the Io plasma torus is presently identified as the source of density fluctuations driving the plasma diffusion outward, in a linearized convection model. This model, which is found to be consistent with the Trauger data, yields simple expressions which encompass the thickness of the source ring, a linear convection cell dimension, and the exponent of the zenocentric radius power law satisfied by the plasma density in the source ring.
Summers, D.↗