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Results for “PLASMA CONDUCTIVITY”

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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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

A possible magnetic wake of Titan - Pioneer 11 observations

The paper deals with measurements of the magnetic field along the outbound leg of Pioneer's trajectory at Saturn, which suggest that the spacecraft may have passed through the magnetic wake of Titan at a distance of 145 Titan radii downstream from Titan. The data obtained over a period of several hours around the crossing of Titan's L shell exhibit a number of characteristics which are qualitatively consistent with predictions based on theories of the interaction between a supersonic magnetized plasma and a conducting or magnetized planetary body. In addition, values of the plasma mass density derived from the interaction geometry are consistent with an upper limit inferred from in situ plasma measurements obtained during the outbound leg of Pioneer's trajectory.

Jones, D. E.↗
NASA NTRS1987

Electrically conductive, black thermal control coatings for spacecraft applications. III - Plasma-deposited ceramic matrix

Five black, electrically-conductive thermal control coatings have been formulated and tested for application on the Galileo spacecraft. The coatings consist of both organic and inorganic systems applied on titanium, aluminum, and glass/epoxy composite surfaces. The coatings were tested under simulated space environment conditions. Coated specimens were subjected to thermal radiation, convective and combustive heating, and cryogenic conditions over a temperature range between -196 C and 538 C. Mechanical, physical, thermal, electrical, and thermooptical properties are presented for one of these coatings. This paper describes the preparation, characteristics, and spraying of iron titanate on titanium and aluminum, and presents performance results.

Hribar, V. F.↗
NASA NTRS1990

Measurement realities of current collection in dynamic space plasma environments

Theories which describe currents collected by conducting and non-conducting bodies immersed in plasmas have many of their concepts based upon the fundamentals of sheath-potential distributions and charged-particle behavior in superimposed electric and magnetic fields. Those current-collecting bodies (or electrodes) may be Langmuir probes, electric field detectors, aperture plates on ion mass spectrometers and retarding potential analyzers, or spacecraft and their rigid and tethered appendages. Often the models are incomplete in representing the conditions under which the current-voltage characteristics of the electrode and its system are to be measured. In such cases, the experimenter must carefully take into account magnetic field effects and particle anisotropies, perturbations caused by the current collection process itself and contamination on electrode surfaces, the complexities of non-Maxwellian plasma distributions, and the temporal variability of the local plasma density, temperature, composition and fields. This set of variables is by no means all-inclusive, but it represents a collection of circumstances guaranteed to accompany experiments involving energetic particle beams, plasma discharges, chemical releases, wave injection and various events of controlled and uncontrolled spacecraft charging. Here, an attempt is made to synopsize these diagnostic challenges and frame them within a perspective that focuses on the physics under investigation and the requirements on the parameters to be measured. Examples include laboratory and spaceborne applications, with specific interest in dynamic and unstable plasma environments.

Szuszczewicz, Edward P.↗
NASA NTRS1993

Stability of the Io plasma torus/atmosphere interaction

The stability of the Io plasma torus-atmosphere interaction is examined. A simple plasma deflection model describes how transients in the plasma flux and the content of the atmosphere affect the ionospheric conductance, limiting the plasma bombardment and, hence, the supply of atmospheric species to the torus. The supply of the torus is seen to be determined by the thermal structure of the plasma, namely, the amount of low energy plasma producing atmospheric erosion vs. that which produces ionization, so that the torus supply rate is not simply proportional to the torus ion density.

Johnson, R. E.↗
NASA NTRS1992

Huygens/ASI plasma wave analyzer capabilities for aerosol measurement

The capabilities of the Huygens Atmospheric Structure Instrument (HASI) are described. These include measurement of atmospheric electrical conductivity by the plasma wave analyzer. How measurement of the atmospheric conductivity can lead to an estimate or the total surface area of the aerosols as a function of altitude is outlined. It is concluded that since the ASI is designed to measure the electrical conductivity as well as the pressure and temperature as a function of altitude, its results should provide a useful check on other instruments that are designed to measure the abundance of aerosols in a limited range of sizes.

Borucki, William J.↗
NASA NTRS2022

Solar Flare Heating with Turbulent Suppression of Thermal Conduction

During solar flares plasma is typically heated to very high temperatures, and the resulting redistribution of energy via thermal conduction is a primary mechanism transporting energy throughout the flaring solar atmosphere. The thermal flux is usually modeled using Spitzer’s theory, which is based on local Coulomb collisions between the electrons carrying the thermal flux and those in the background. However, often during flares, temperature gradients become sufficiently steep that the collisional mean free path exceeds the temperature gradient scale size, so that thermal conduction becomes inherently non-local. Further, turbulent angular scattering, which is detectable in nonthermal widths of atomic emission lines, can also act to increase the collision frequency and so suppress the heat flux. Recent work by Emslie & Bian (2018) extended Spitzer’s theory of thermal conduction to account for both non-locality and turbulent suppression. We have implemented their theoretical expression for the heat flux (which is a convolution of the Spitzer flux with a kernel function) into the RADYN flare-modeling code and performed a parameter study to understand how the resulting changes in thermal conduction affect flare dynamics and hence the radiation produced. We find that models with reduced heat fluxes predict slower bulk flows, less intense line emission, and longer cooling times. By comparing features of atomic emission lines predicted by the models with Doppler velocities and nonthermal line widths deduced from a particular flare observation, we find that models with suppression factors between 0.3 to 0.5 relative to the Spitzer value best reproduce observed Doppmission lines forming over a wide range of temperatures. Interestingly, the model that best matches observed nonthermal line widths has a kappa-type velocity distribution function.

Joel C. Allred↗
NASA NTRS2022

Solar Flare Heating with Turbulent Suppression of Thermal Conduction

During solar flares plasma is typically heated to very high temperatures, and the resulting redistribution of energy via thermal conduction is a primary mechanism transporting energy throughout the flaring solar atmosphere. The thermal flux is usually modeled using Spitzer’s theory, which is based on local Coulomb collisions between the electrons carrying the thermal flux and those in the background. However, often during flares, temperature gradients become sufficiently steep that the collisional mean free path exceeds the temperature gradient scale size, so that thermal conduction becomes inherently non-local. Further, turbulent angular scattering, which is detectable in nonthermal widths of atomic emission lines, can also act to increase the collision frequency and so suppress the heat flux. Recent work by Emslie & Bian (2018) extended Spitzer’s theory of thermal conduction to account for both non-locality and turbulent suppression. We have implemented their theoretical expression for the heat flux (which is a convolution of the Spitzer flux with a kernel function) into the RADYN flare-modeling code and performed a parameter study to understand how the resulting changes in thermal conduction affect flare dynamics and hence the radiation produced. We find that models with reduced heat fluxes predict slower bulk flows, less intense line emission, and longer cooling times. By comparing features of atomic emission lines predicted by the models with Doppler velocities and nonthermal line widths deduced from a particular flare observation, we find that models with suppression factors between 0.3 to 0.5 relative to the Spitzer value best reproduce observed Doppler velocities across emission lines forming over a wide range of temperatures. Interestingly, the model that best matches observed nonthermal line widths has a kappa-type velocity distribution function

Solar flares↗
NASA NTRS1976

Parametric dependence of ion temperature and relative density in the NASA Lewis SUMMA facility

Further hot-ion plasma experiments were conducted in the SUMMA superconducting magnetic mirror facility. A steady-state plasma with mutually perpendicular magnetic and electric fields was formed by applying a strong radially inward dc electric field between cylindrical anodes and hollow cathodes located near the magnetic mirror maxima. Extending the use of water cooling to the hollow cathodes, in addition to the anodes, resulted in higher maximum power input to the plasma. Steady-state hydrogen plasmas with ion kinetic temperatures as high as 830 eV were produced. Functional relations were obtained empirically among the plasma current, voltage, magnetic flux density, ion temperature, and relative ion density. The functional relations were deduced by use of a multiple correlation analysis. Data were obtained for midplane magnetic fields from 0.5 to 3.37 tesla and input power up to 45 kW. Also, initial absolute electron density measurements are reported from a 90 deg Thomson scattering laser system.

Snyder, A.↗
NASA NTRS1993

Mergers, cooling flows, and evaporation

Mergers (the capture of cold gas, especially) can have a profound influence on the hot coronal gas of early-type galaxies and clusters, potentially inducing symptoms hitherto attributed to a cooling flow, if thermal conduction is operative in the coronal plasma. Heat can be conducted from the hot phase into the cold phase, simultaneously ionizing the cold gas to make optical filaments, while locally cooling the coronal gas to mimic a cooling-flow. If there is heat conduction, though, there is no standard cooling-flow since radiative losses are balanced by conduction and not mass deposition. Amongst the strongest observational support for the existence of cooling-flows is the presence of intermediate temperature gas with x-ray emission-line strengths in agreement with cooling-flow models. Here, x-ray line strengths are calculated for this alternative model, in which mergers are responsible for the observed optical and x-ray properties. Since gas around 10(exp 4) K is thermally stable, the cold cloud need not necessarily evaporate and hydrostatic solutions exist. Good agreement with the x-ray data is obtained. The relative strengths of intermediate temperature x-ray emission lines are in significantly better agreement with a simple conduction model than with published cooling-flow models. The good agreement of the conduction model with optical, infrared and x-ray data indicates that significantly more theoretical effort into this type of solution would be profitable.

Sparks, W. B.↗
NASA NTRS1983

Plasma boundaries and shocks

Work conducted over the past four years on the plasma and magnetic field boundaries in the earth's magnetosphere and interplanetary space is reviewed. Studies of the structure and dynamics of bow shocks based largely on ISEE-1 and -2 measurments are discussed, together with intensive investigations of the particles and waves of the foreshock region, marked by various distributions of return ions reflected from the bow shock. Attention is briefly given to interplanetary shocks and the magnetosheath region, while research on the location, motion and structure and flux transfer events in the magnetopause and on the magnetospheric boundary layer is considered in detail. Evidence of reconnection in the magnetosphere is discussed, and studies of processes in the plasma sheet and neutral sheet in the magnetotail, the polar cusp and the injection of plasma into the inner magnetosphere are noted.

Russell, C. T.↗
NASA NTRS1976

Parametric dependence of ion temperature and relative density in the NASA Lewis SUMMA facility

Further hot-ion plasma experiments were conducted in the SUMMA superconducting magnetic mirror facility. A steady-state ExB plasma was formed by applying a strong radially inward dc electric field between cylindrical anodes and hollow cathodes located near the magnetic mirror maxima. Extending the use of water cooling to the hollow cathodes, in addition to the anodes, resulted in higher maximum power input to the plasma. Steady-state hydrogen plasmas with ion kinetic temperatures as high as 830 eV were produced. Functional relations were obtained empirically among the plasma current, voltage, magnetic flux density, ion temperature, and relative ion density. The functional relations were deduced by use of a multiple correlation analysis. Data were obtained for midplane magnetic fields from 0.5 to 3.37 tesla and input power up to 45 kW. Also, initial absolute electron density measurements are reported from a 90 deg Thomson scattering laser system.

Snyder, A.↗
NASA NTRS1981

Bodies in flowing plasmas - Laboratory studies

A brief review of early rudimentary laboratory studies of bodies in flowing, rarefied plasmas is presented (e.g., Birkeland, 1908), along with a discussion of more recent parametric studies conducted in steady plasma wind tunnels, which includes the study by Hall et al. (1964), in which a strong ion density enhancement in the center of the ion void created downstream from the body was observed. Good agreement was found between the experimental results and theoretical calculations which omit ion thermal motion. Examples in which in situ data on the interaction between satellites and the ionospheric plasma have been elucidated by the laboratory results are presented, and include evidence for a midwake axial ion peak, and ion current density in the near-wake region. The application of the ionospheric laboratory to basic space plasma physics is discussed, and its application to some types of solar system plasma phenomena is illustrated.

Stone, N. H.↗
NASA NTRS1993

(abstract) 3D Electromagnetic Plasma Particle Simulations

A 3D electromagnetic plasma particle-in-cell code has been developed using the General Concurrent PIC algorithm. The GCPIC algorithm uses a domain decomposition to divide the computation among the processors. Particles must be exchanged between processors as they move. The efficiencies for 1-, 2-, and 3-dimensional partitions of the three dimensional domain are compared, and the algorithm is found to be very efficient even when a large fraction (e.g., 30%) of the particles must be exchanged at every time step. This PIC code has been used to perform simulations of a variety of space plasma physics problems. Results of three applications will be discussed: 1) plasma disturbances induced by moving conducting bodies in a magnetized plasma; 2) plasma plume interactions; and 3) solar wind termination shock.

electromagnetic plasma particles simulations 3D al↗