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NASA NTRS1994

Statistical uncertainties in temperature diagnostics for hot coronal plasma using the ASCA SIS

Statistical uncertainties in determining the temperatures of hot (0.5-10 keV) coronal plasmas are investigated. The statistical presicion of various spectral temperature diagnostics is established by analyzing synthetic ASCA solid-state imaging spectrometer (SIS) CCD spectra. The diagnostics considered are the ratio of hydrogen-like to helium-like line complexes of Z greater than or = 14 elements, line-free portions of the continuum, and the entire spectrum. While fits to the entire spectrum yield the highest statistical precision, it is argued that fits to the line-free continuum are less susceptible to atomic data uncertainties but lead to a modest increase in statistical uncertainty over full spectral fits. Temperatures deduced from line ratios can have similar accuracy, but only over a narrow range of temperatures. Convenient estimates of statistical accuracies for the various temperature diagnostics are provided which may be used in planning ASCA SIS observations.

Swartz, Douglas A.↗

NASA NTRS1994

Two-temperature X-ray emission from the planetary nebula NGC 7293

ROSAT Position Sensitive Proportional Counter (PSPC) observations of the planetary nebula NGC are reported here. This planetary nebula is here the first discovered to show clearly two components in its X-ray spectrum. A two-component model consisting of a blackbody and a Raymond-Smith thermal plasma is fitted to the observed ROSAT PSPC spectrum. This results in a temperature of T(sub 1) = 1.4 x 10(exp 5) K for the blackbody component and a temperature T(sub 2) = 8.7 x 10(exp 6) K for the hot plasma component, at a hydrogen column density N(sub H) = 1.4 x 10(exp 20)/sq cm. The temperature of the blackbody component is consistent with the helium Zanstra temperature of the central star, indicating that it may be attributed to the photosphere of the central star. The high-temperature component is possibly from a corona around the central star, which may be related to a strong convection in the star. An alternative explanation is that the hot plasma resides in a hot bubble predicted by the interacting wind model. A lower limit of the electron density in the hot plasma is found to be approximately 10/cu cm.

Leahy, D. A.↗

NASA NTRS1996

Effects of Shocks on Emission from Central Engines of Active Galactic Nuclei. I

In this paper we show that perturbations of the accretion flow within the central engines of some active galactic nuclei (AGNS) are likely to form shock waves in the accreting plasma. Such shocks, which may be either collisional or collisionless, can contribute to the observed high-energy temporal and spectral variability. Our rationale is the following: Observations show that the continuum emission probably originates in an optically thin, hot plasma in the AGN central engine. The flux and spectrum from this hot plasma varies significantly over light crossing timescales. Several authors have suggested that macroscopic perturbations contained within this plasma are the sources of this variability. In order to produce the observed emission the perturbations must be radiatively coupled with the optically thin hot matter and must also move with high velocities. We suggest that shocks, which can be very effective in randomizing the bulk motion of the perturbations, are responsible for this coupling. Shocks should form in the central engine, because the temperatures and magnetic fields are probably reduced below their virial values by radiative dissipation. Perturbations moving at Keplerian speeds, or strong non-linear excitations, result in supersonic and super-Alfvenic velocities leading to shock waves within the hot plasma. We show that even a perturbation smaller than the emitting region can form a shock that significantly modifies the continuum emission in an AGN, and that the spectral and temporal variability from such a shock generally resembles those of radio-quiet AGNS. As an example, the shock inducing perturbation in our model is a small main-sequence star, the capturing and eventual accretion of which are known to be a plausible process. We argue that shocks in the central engine may also provide a natural triggering mechanism for the "cold" component of Guilbert & Rees two-phase medium and an efficient mecha- nism for angular momentum transfer. Current and future missions, such as ASCA, XTE, XMM, AXAF, and ASTRO-E may determine the importance of shock-related emission from the central engines of AGNS.

Sivron, R.↗

NASA NTRS1977

Neutron monitoring and electrode calorimetry experiments in the HIP-1 Hot Ion Plasma

Results are presented for two diagnostic procedures on HIP-1: neutron diagnostics to determine where neutrons originated within the plasma discharge chamber and electrode calorimetry to measure the steady-state power absorbed by the two anodes and cathodes. Results are also reported for a hot-ion plasma formed with a continuous-cathode rod, one that spans the full length of the test section, in place of the two hollow cathodes. The outboard neutron source strength increased relative to that at the midplane when (1) the cathode tips were moved farther outboard, (2) the anode diameters were increased, and (3) one of the anodes was removed. The distribution of neutron sources within the plasma discharge chamber was insensitive to the division of current between the two cathodes. For the continuous cathode, increasing the discharge current increased the midplane neutron source strength relative to the outboard source strength. Each cathode absorbed from 12 to 15 percent of the input power regardless of the division of current between the cathodes. The anodes absorbed from 20 to 40 percent of the input power. The division of power absorption between the anodes varied with plasma operating conditions and electrode placement.

Reinmann, J. J.↗

NASA NTRS1977

Evolution of the high-temperature plasma in the 15 June 1973 flare

The evolution of the high-temperature plasma in the solar flare of June 15, 1973, is analyzed using XUV spectroheliograms obtained from Skylab. Preflare enhancement of loops in the active region is discussed, and the temperature and density of the hot plasma are determined as a function of time. The turbulent velocity in the high-temperature plasma is deduced from a comparison of line widths of the Fe XXIV doublet at 192 and 255 A. The results indicate that: (1) the flare occurred in a low-lying loop or loops; (2) the large-scale magnetic-field configuration of the active region did not change significantly; (3) the hot plasma observed in Fe XXIII-XXIV showed considerable dynamic activity, including an initial upward motion of the whole plasma with a velocity of about 80 km/s; (4) large turbulent mass motions took place in the Fe XXIII-XXIV plasma with random velocities of 100 to 160 km/s; (5) the temperature of the hot plasma was 14 million K at peak X-ray intensity, decreased slightly, and then remained at 12.6 million K before dropping to below 10 million K; and (6) there was a temperature gradient along the length of the loop, with the 14 million-K plasma near the top and progressively lower-temperature plasmas on either side.

Cheng, C.-C.↗

NASA NTRS1985

A tandem mirror plasma source for a hybrid plume plasma propulsion concept

This paper describes a tandem mirror magnetic plasma confinement device to be considered as a hot plasma source for the hybrid plume rocket concept. The hot plasma from this device is injected into an exhaust duct, which will interact with an annular layer of hypersonic neutral gas. Such a device can be used to study the dynamics of the hybrid plume and to experimentally verify the numerical predictions obtained with computer codes. The basic system design is also geared toward being lightweight and compact, as well as having high power density (i.e., several kW/sq cm) at the exhaust. This feature is aimed toward the feasibility of 'space testing'. The plasma is heated by microwaves. A 50 percent heating efficiency can be obtained by using two half-circle antennas. The preliminary Monte Carlo modeling of test particles result reported here indicates that interaction does take place in the exhaust duct. Neutrals gain energy from the ion, which confirms the hybrid plume concept.

Yang, T. F.↗

NASA NTRS1981

The diffuse extreme-ultraviolet background - Constraints on hot coronal plasma

The Apollo-Soyuz data and data reported by Cash et al. (1976) have been reanalyzed in terms of both isothermal models and temperature distribution models. In the latter case, a power-law form is assumed for the relation between emission measure and temperature. A new upper limit on diffuse flux in the 20-73 eV band derived from Apollo-Soyuz observations made in the earth's shadow has been incorporated in the calculation. In the considered investigation the results of the new analysis are presented and the implications for the physical properties of the hot component of the interstellar medium are discussed. The analysis of the Berkeley extreme ultraviolet (EUV) diffuse background measurements using either isothermal or power law temperature distribution models for the emitting plasma indicates excellent qualitative agreement with hard X-ray data that suggest the sun to be immersed in a hot plasma that pervades most of space out to approximately 100 pc.

Paresce, F.↗

DOE OSTI2025

Group Conductivity and Nonadiabatic Born Effective Charges of Disordered Metals, Warm Dense Matter, and Hot Dense Plasma

The average ionization state is a critical parameter in plasma models for charged particle transport, equations of state, and optical response. The dynamical or nonadiabatic Born effective charge (NBEC), calculated via first principles time-dependent density-functional theory, provides exact ionic partitioning of bulk electron response for both metallic and insulating materials. The NBEC can be transformed into a “group conductivity,” i.e., the electron conductivity ascribed to a subset of ions. We show that for disordered metallic systems, such as warm dense matter (WDM) and hot dense plasma, the static limit of the NBEC is different from the average ionization states, but that the ionization state can be extracted from the group conductivity even in mixed systems. Here we demonstrate this approach using a set of archetypical examples, including cold and warm aluminium, low- and high-density WDM carbon, and a WDM carbon-beryllium-hydrogen mixture.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS2004

The Solar Flare 4: 10 keV X-ray Spectrum

The 4-10 keV solar flare spectrum includes highly excited lines of stripped Ca, Fe, and Ni ions as well as a continuum steeply falling with energy. Groups of lines at approximately 7 keV and approximately 8 keV, observed during flares by the broad-band RHESSI spectrometer and called here the Fe-line and Fe/Ni-line features, are formed mostly of Fe lines but with Ni lines contributing to the approximately 8 keV feature. Possible temperature indicators of these line features are discussed - the peak or centroid energies of the Fe-line feature, the line ratio of the Fe-line to the Fe/Ni-line features, and the equivalent width of the Fe-line feature. The equivalent width is by far the most sensitive to temperature. However, results will be confused if, as is commonly believed, the abundance of Fe varies from flare to flare, even during the course of a single flare. With temperature determined from the thermal continuum, the Fe-line feature becomes a diagnostic of the Fe abundance in flare plasmas. These results are of interest for other hot plasmas in coronal ionization equilibrium such as stellar flare plasmas, hot gas in galaxies, and older supernova remnants.

Phillips, K. J. H.↗

NASA NTRS1982

Plasma pitch angle distributions near the substorm injection front

ATS-6 spacecraft hot plasma instrument data obtained during January, 1980 is presented, which provides electron and ion pitch distributions in the vicinity of an earthward-propagating, substorm-associated abrupt plasma change near synchronous orbit. Evidence is found of symmetric atmospheric source cones for few 100-eV electrons after front passage, supporting both (1) concept of atmospheric electron degradation of the hot, high-altitude plasma, and (2) the proposal that the injection front is a moving, precipitation-flow boundary between the hot plasma and the cooler plasma that has become spectrally degraded via interaction with the atmosphere. The enhanced hot plasma electron intensities appearing in association with front passage exhibit a modest, field-aligned anisotropy with minima at pitch angles characteristic of symmetric loss cones, consistent with mirror compression of the electrons on inward-collapsing field lines.

Moore, T. E.↗

NASA NTRS1994

Analysis of plasma measurements for the Geotail mission

The CPI plasma measurements from the Geotail spacecraft are currently used by a number of scientists in support of varied research projects. Measurements from the CPI hot plasma analyzer have been processed to compute one-minute averages of plasma densities, temperatures, and velocities for the period 1 Oct. 1992 - 31 July 1993. These parameters are used in a preliminary survey of the magnetotail for distances from earth of 10 to 210 earth radii. The cold plasmas within the magnetotail drift towards the midplane and are thought to be a principal source for the hot plasma sheet. A remarkable result from Geotail is the observation of cold ion beams coexisting as distinct components in the presence of hot plasma-sheet plasmas. The development and evolution of plasmoids is a topic of considerable interest in studies of the magnetotail and magnetospheric substorms. A number of possible plasmoids have been identified in the Geotail data set based upon reversals of the Z component of the magnetic field as observed with the MGF instrumentation. An intensive study of the electron and ion velocity distributions and the plasma parameters for several of these events reveals unexpected features. Collaborative work with several Geotail instrument teams and other researchers is also ongoing.

Frank, Louis A.↗

NASA NTRS1989

Hot ion plasmas from the cloud of neutral gases surrounding the Space Shuttle

Large intensities of hot positive ions are observed out to distances of several hundred meters from the Space Shuttle with a plasma analyzer on a small free-flying satellite, the Plasma Diagnostics Package. This ion plasma is inferred to be generated by the charge exchange of ionospheric O+ ions with a large cloud of water molecules from the Space Shuttle. The measured ion density ranges from about 30 to 10,000 H2O+ ions/cu cm. A model for the water vapor cloud provides the basis for density estimates as high as 10 to the 9th H2O molecules/cu cm at a distance of 50 m from the Space Shuttle. Thus, the Space Shuttle possesses a substantial coorbiting atmosphere.

Paterson, W. R.↗

NASA NTRS1982

Plasma injection and transport in the mid-altitude polar cusp

DE-1 hot plasma observations in the mid-altitude polar cusp have shown evidence of a significant velocity filtering phenomenon which is consistent with a latitudinally narrow region of plasma injection located at a geocentric distance of about eight earth radii (in a dipole approximation). Plasma convection from the injection region into the polar cap results in a V-shaped log E vs. observed pitch angle relation at geocentric distances near 4 earth radii. This velocity filtering effect allows the measurement of much smaller flow velocities (about 10 km/sec) than have heretofore been possible with hot plasma measurements. The flows thus determined are consistent with ionospheric flows measured nearly simultaneously by the DE-2 spacecraft, although the magnitudes of the higher altitude flows are higher by a factor of 2 or more than an approximately r to the 3/2 power dipole-field mapping would predict.

Burch, J. L.↗

NASA NTRS1992

Dust-gas interactions and the infrared emission from hot astrophysical plasmas

Environments where the presence of dust is primarily inferred from its collisional interactions with the ambient gas are reviewed with emphasis on environments typically encountered behind fast (100 km/s or greater) shocks and in hot (few 10 exp 5 K) plasmas in galactic halos, some elliptical galaxies, or the intergalactic medium of galaxy clusters. The discussion covers interactions between dust grains and a hot gas, grain temperatures and infrared emission, supernova remnants and supershells, and dust and hot gas in, around, and between galaxies. Finally, future prospects in the field are briefly discussed.

Dwek, Eli↗

NASA NTRS1994

Comprehensive Plasma Instrumentation (CPU) for the Geotail spacecraft

Geotail was launched on 24 July 1992 as the first new spacecraft of the International Solar Terrestrial Physics Program (ISTP). A primary objective of the Geotail mission is the acquisition of particles and fields measurements in the tail region of the magnetosphere. Some of the specific scientific objectives of the Geotail mission are; (1) assessment of the relative importance of solar-wind and ionospheric sources to the plasmas of the magnetotail, (2) a search for plasmoids and flux ropes, (3) direct observation of the effects of plasma acceleration and heating in the current sheet, and (4) measurements of currents and convective flows carried by magnetotail plasmas. The Comprehensive Plasma Instrumentation (CPI) aboard the Geotail spacecraft provides observations of the charged particles that comprise the plasma populations of the magnetosphere and the solar wind. In many cases the physical processes that contribute to the flow of energy and mass through the Solar-Terrestrial plasma system can be understood only through a detailed examination and analysis of the distribution of the particle velocities in the ambient plasmas. The CPI provides detailed measurements of these distributions. It employs three plasma analyzers: (1) the Hot Plasma analyzer (CPI-HP) for hot electrons and ions found in the plasma sheet and the inner magnetosphere; (2) a Solar Wind analyzer (CPI-SW) for cool plasmas with high bulk speeds such as those found in the solar wind and magnetosheath; and (3) an Ion Composition analyzer (CPI-IC) for identification of ion species such as H(+), He(+), He(++), and O(+). Along with measurements from other fields and particles instrumentation on Geotail, the CPI measurements provide a fundamental experimental base for investigations of solar-terrestrial plasmas and fields.

Frank, Louis A.↗

NASA NTRS1995

First spectral observations of the diffuse background with the Extreme Ultraviolet Explorer

We present the first results from the analysis of the spectroscopic observations of diffuse extreme ultraviolet (EUV) emission taken with the Extreme Ultraviolet Explorer (EUVE) spectrometers in the wavelength range 160-740 A. Although not designed or optimized for diffuse observation, the EUVE spectrometers are the most sensitive diffuse EUV spectrometer in orbit. The spectral resolution for diffuse emission of the medium and long-wavelength spectrometers are 17 and 34 A FWHM, respectively. During the period from 1992 July 25 to 1992 August 19, the spectrometers surveyed a 2 x 20 deg field scanned from (l, b) = (24 deg, -28 deg) to (44 deg, -74 deg) with a total effective exposure time of 575,232 s. The only emission lines detected were those of He I and He II (584, 537, 304 A) with intensities consistent with local geocoronal and/or interplanetary scattering of solar radiation (584 A = 1.30 rayleighs; 537 A = 0.040 R; and 304 A = 0.029 R). Models of the soft X-ray background, which results from a 10(exp 6) K plasma (Local Bubble) surrounding the neutral gas near the Sun (Local Cloud), predict that most of the flux from the hot plasma appears as emission lines in the EUV. We have compared these spectral predictions with our observations to place limits on the emission measure versus temperature of the proposed hot plasma. Using the same plasma model, we derived emissions measures for our data and the C and B soft X-ray bands of the Wisconsin rocket survey. We find that our limits for the plasma emission measure are a factor of 5-10 below the C- and B-band emission measures over the temperature range from 10(exp 5.7) to 10(exp 6.4) K. We explore possible scenarios that could reconcile our results with the X-ray surveys and conclude that depletion or a nonequilibrium plasma state rather than absorption are the more likely explanations of the discrepancy. We also show that our spectrum is inconsistent with the spectrum from the approximately 10(exp 5) K gas at the conductive interface between the hot Local Bubble and the cooler Local Cloud given by Slavin (1989). In addition, we place new limits on the helium ionization parameter in the Sun's vicinity caused by the 10(exp 6) K plasma in the Local Bubble.

Jelinksy, P.↗

NASA NTRS1992

Initial signatures of magnetic field and energetic particle fluxes at tail reconfiguration - Explosive growth phase

The initial signatures of tail field reconfiguration observed in the near-earth magnetotail are examined using data obtained by the AMPTE/CCE magnetometer and the Medium Energy Particle Analyzer. It is found that the tail reconfiguration events could be classified as belonging to two types, Type I and Type II. In Type I events, a current disruption is immersed in a hot plasma region expanding from inward (earthward/equatorward) of the spacecraft; consequently, the spacecraft is immersed in a hot plasma region expanding from inward. The Type II reconfiguration event is characterized by a distinctive interval (explosive growth phase) just prior to the local commencement of tail phase.

Ohtani, S.↗

NASA NTRS1991

Heat sink effects in variable polarity plasma arc welding

The Space Shuttle External Tank is fabricated by the variable polarity plasma arc (VPPA) welding process. In VPPA welding, a noble gas, usually argon, is directed through an arc to emerge from the torch as a hot plasma jet. This jet is surrounded by a shielding gas, usually helium, to protect the weld from contamination with air. The high velocity, hot plasma jet completely penetrates the workpiece (resembling a line heat source) when operated in the 'keyhole' mode. The metal melts on touching the side of the jet, as the torch travels in the perpendicular direction to the direction of the jet, and melted metal moves around the plasma jet in the keyhole forming a puddle which solidifies behind the jet. Heat sink effects are observed when there are irregularities in the workpiece configuration, especially, if these irregularities are close to the weld bead. These heat sinks affect the geometry of the weld bead, i.e., in extreme cases they could cause defects such as incomplete fusion. Also, different fixtures seem to have varying heat sink effects. The objective of this research is to study the effect of irregularities in workpiece configuration and fixture differences (heat sink effects) on the weld bead geometry with the ultimate objective to compensate for the heat sink effects and achieve a perfect weld. Experiments were performed on different workpiece geometries and compared to approximate models.

Abdelmessih, Amanie N.↗