Dynamics of arc ignition and cathode spot movement of thermionically emitting cathode surfaces
Arc ignition and cathode spot movement dynamics of thermionically emitting cathode surfaces in heat feedback plasma
Cheng, D. Y.↗
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Design of the particles experiment subsystem of the Apollo lunar subsatellite.
In August 1971 an eighty pound subsatellite was ejected from Apollo 15 into lunar orbit. The subsatellite is expected to remain in lunar orbit for at least one year. The Particles Experiment Subsystem of the subsatellite was designed to implement the Particle Shadows/Boundary Layer Experiment. The objective of the experiment is to obtain data for the study of the formation and the dynamics of the earth's magnetosphere, the interaction of plasmas with the moon, and the physics of solar flares. The design of the particle detector telescopes is considered together with details of collimator design, silicon detectors, the absorber foil, and the power subsystems. The instrument performance in lunar orbit is discussed.
Baum, J. J.↗
Lunar perturbations in columnar electron content and their interpretation in terms of dynamo electrostatic fields
Both the sun and the moon exert influences on the ionosphere, causing fluctuations in its electron content. The small lunar effects, though not negligible, are difficult to analyze because their periodicities differ little from the periodicity of the dominant solar effects. A finite duration impulse response filter was perfected, permitting the efficient splitting of our columnar electron content data into a solar, a lunar, and a residual component. The solar component plus the lunar component and the solar component alone were processed by a dynamic ionospheric simulation program that yields values of vertical plasma drifts when electron content data are used as input. The difference between the two plasma drifts so obtained was taken as being the plasma drift caused by the electric field generated by the lunar tides in the dynamo region. This technique appears to be the first to allow a direct estimation of the lunar-induced electric fields in the ionosphere.
Bernhardt, P. A.↗
Determination of thermospheric quantities from simple ionospheric observations using numerical simulation
Measured ionospheric electron content and peak electron concentration data are introduced into a numerical simulation of the ionosphere to yield values of induced plasma drifts and exospheric neutral temperatures consistent with the observations. Data collected on 23-24 March 1970 on the East Coast of the U.S.A. are analyzed and the results are in agreement with incoherent radar measurements at Millstone Hill, Massachusetts. Neutral winds and meridional exospheric temperature gradients that give rise to the computed plasma drifts are calculated through the use of a dynamic model of the thermosphere.
Antoniadis, D. A.↗
Dust-magnetospheric interactions
The important processes controlling the electrical potentials of dust grains in planetary magnetospheres are considered, and the quasi-equilibrium electric potentials acquired by them in the different plasma and radiative environments encountered are evaluated. The orbital dynamics of such charged grains is discussed, and their interaction with satellites within the planetary magnetospheres is considered. The possibility of magneto-gravitational capture of these gains by magnetospheres, to form dust rings around the planets, is also discussed. Finally, the possible break-up of grains charged to large electrical potentials and its consequences are briefly addressed.
Mendis, D. A.↗
Io's sodium emission cloud and the Voyager 1 encounter
Monitoring of Io's neutral sodium emission cloud, monitored from two earth observatories during the period of the Voyager 1 encounter, demonstrated that the behavior of the cloud is complex; displaying a variety of changes, both systematic and secular, which can have both time and spatial dependencies while also possessing some characteristics of stability. Dynamic models of the sodium cloud employing Voyager 1 plasma data provide a reasonable fit to the encounter images of one of the observatories. The modeling assumptions of anisotropic ejection of neutral sodium atoms from the leading, inner hemisphere of Io, with a velocity distribution characteristic of sputtering, adequately explain the overall intensity distribution of the 'near cloud'.
Goldberg, B. A.↗
On charge exchange and knock-on processes in the exosphere of Io
One direct consequence of magnetospheric interaction of Io is the strong dynamical coupling of its neutral atmosphere with the corotating plasma. The absorption of the thermal ions and the associated neutral injection is an improtant issue not yet explored. As far as nonthermal escape of the neutral atmosphere is concerned, three processes stand out. That is, apart from sputtering, exospheric interactions like atom-ion knock-on collision and charge exchange recombination could be a significant source of the neutral clouds in the Jovian system. Using a current electrodynamic model of Io, both the absorption rate of the corotating thermal plasma and the production rates of new exospheric ions and the fast neutrals are considered. It is found that the source strength of the neutral atoms and molecules with speeds of about 100 km/sec could amount to 10 to the 26th/sec whereas exospheric neutrals emitted at lower speed (of about 10 km/sec) amounts to 4 x 10 to the 25th/sec. The generation of the new ions in connection with the streaming of the magnetospheric plasma around Io could also produce an asymmetric sputtering with a neutral flux of about 10 to the 27th/sec emitted from the region of Io which faces Jupiter. These results may be related to a number of sodium observations.
Ip, W.-H.↗
A two-dimensional model of the ionosphere of Venus
While most orbits of the Pioneer Venus Orbiter have indicated a substantial nightside ionosphere, this region virtually disappears, existing only as irregular patches of low density plasma, on those orbits during which the solar wind dynamic pressure is large. There observational results are presently interpreted by means of a two-dimensional theoretical model of the Venus ionosphere in which empirical horizontal velocities are adopted. The degree to which the horizontal transport of ions from day to night can maintain the nightside ionosphere is shown to depend on the flow velocities, together with the ionopause height at the terminator. Attention is also given to the role played by electron precipitation in the support of a nightside ionosphere. Indirect evidence is given for an enhanced deuterium/hydrogen ratio on Venus.
Cravens, T. E.↗
Incoherent scatter observations of an artificially modified ionosphere
The 'experiment of opportunity' to test incoherent scatter radar techniques for the diagnostic study of a chemically induced modification of the ionosphere occasioned by the launch of the HEAO-C satellite is described. The optimal utilization of a steerable incoherent scatter radar for a short duration event is examined. The choice of keeping the antenna fixed to obtain good control data and excellent time resolution along a given direction versus scanning the antenna to obtain mixed spatial and temporal morphologies is discussed. Results for fixed position measurements, elevation scans, ion-drift, and total electron content are presented. The first unambiguous observations of a gas expansion 'snowplow effect' is reported along with the derivation of local and height-integrated plasma recombination rates and the full spatial, temporal, and dynamical morphologies of a large-scale ionospheric hole.
Wand, R. H.↗
The Origins of Plasmas in the Earth's Neighborhood (OPEN) program
The nature and objectives of the OPEN program are overviewed. The Origins of Plasmas in the Earth's Neighborhood program was conceived in 1979 and proposed as a major new initiative to study the energetics of the earth's space environment by the end of the 1980s. The objectives of OPEN have been integrated into the Global Geospace Study (GGS) segment to the International Solar-Terrestrial Physics (ISTP) program now being planned jointly by NASA, ESA, and Japan. The goals will be to develop a global understanding of the flow of energy from the sun through the earth's space environment above the neutral atmosphere and to define the cause and effect relationships between the plasma physics processes that link different regions of this dynamic environment. A network of four spacecraft will be used, each one carrying an instrument complement to characterize the composition and behavior of the upstream solar wind, the high-altitude polar magnetosphere, the equatorial magnetosphere, and the comet-like geomagnetic tail. Multispectral cameras will also be carried to image polar auroras at ultraviolet, visible and X-ray wavelengths. Experimentalists and theorists on the international team will participate.
Alexander, J. K.↗
Electrostatic charging of electrically active spacecraft
A model is presented which predicts the temporal behavior of the ionospheric charging of spacecraft which eject energetic positive ions. The dynamic interaction of the spacecraft with the space-plasma environment is modelled as an equivalent electrical circuit consisting of a variable capacitor in parallel with two current sources. The spacecraft/space-plasma sheath is modelled as a variable capacitor containing positive-ion space charge. The ejection of energetic positive ions from the spacecraft represents a current source which charges the capacitor. Return current collected from the space-plasma sheath to the spacecraft is modelled as a variable current source which discharges the capacitor. The model can predict the temporal behavior of sheath movement, spacecraft potential, and space-plasma return current for a wide range of altitude, duty cycle, and ejected positive-ion current. Experimentally measured charging results, obtained for the Satellite Positive Ion Beam System (SPIBS) rocket flight, are accurately predicted by the model. Anticipated vehicle charging levels are presented for neutral-particle-beam platforms operating with a net, unneutralized, positive-ion-current component present in the emitted neutral-particle beam.
Matossian, J. N.↗
Correlated observations of impulsive UV and hard X-ray bursts from the solar maximum mission
The spatially resolved UV observations and hard X-ray observations are analyzed in order to study the spatial structure and physical conditions in the UV and hard X-ray sources. The data reveal that impulsive UV emissions and hard X-ray bursts occur in small kernels. Individual light curves for Si IV and hard X-ray emissions are compared and it is detected that the individual peaks in the curves correspond. The dynamic evolution and density diagnostics of the transition zone plasmas are examined.
Cheng, C.-C.↗
A particle astrophysics magnet facility: ASTROMAG
The primary scientific objectives of ASTROMAG are to: examine cosmological models by searching for antimatter and dark matter candidates; study the origin and evolution of matter in the galaxy by direct sampling of galactic matter; and study the origin and acceleration of the relativistic particle plasma in the galaxy and its effects on the dynamics and evolution of the galaxy. These general scientific objectives will be met by ASTROMAG with particle detection instruments designed to make the following observations: search, for anti-nuclei of helium and heavier element; measure the spectra of anti-protons and positrons; measure the isotopic composition of cosmic ray nuclei at energies of several GeV/amu; and measure the energy spectra of cosmic ray nuclei to very high energies.
Ormes, Jonathan F.↗
The ionospheric effects of a weak intrinsic magnetic field at Mars
An improved model of the Martian ionosphere which allows the magnetic field to have any direction in the horizontal plane is presented, as well as results of calculations for several different intrinsic magnetic field strengths and directions. When the solar wind dynamic pressure exceeds the Martian ionospheric thermal pressure, the plasma motion is weakly downward throughout the ionosphere for the case of no intrinsic magnetic field, but when the intrinsic and induced fields are in opposite directions, the plasma flow tends to converge toward the current sheet. As a consequence of this convergence, the plasma density is somewhat enhanced near the current sheet, which is located near an altitude of 170 km. The ionosphere above an altitude of about 190 km is not significantly affected by the existence of an intrinsic field as weak as 60 nT.
Shinagawa, H.↗
By-controlled convection and field-aligned currents near midnight auroral oval for northward interplanetary magnetic field
Using the Dynamics Explorer (DE) 2 magnetic and electric field and plasma data, B(sub y)- controlled convection and field-aligned currents in the midnight sector for northward interplanetary magnetic field (IMF) are examined. The results of an analysis of the electric field data show that when IMF is stable and when its magnitude is large, a coherent B(sub y)-controlled convection exists near the midnight auroral oval in the ionosphere having adequate conductivities. When B(sub y) is negative, the convection consists of a westward (eastward) plasma flow at the lower latitudes and an eastward (westward) plasma flow at the higher latitudes in the midnight sector in the northern (southern) ionosphere. When B(sub y) is positive, the flow directions are reversed. The distribution of the field-aligned currents associated with the B(sub y)-controlled convection, in most cases, shows a three-sheet structure. In accordance with the convection the directions of the three sheets are dependent on the sign of B(sub y). The location of disappearance of the precipitating intense electrons having energies of a few keV is close to the convection reversal surface. However, the more detailed relationship between the electron precipitation boundary and the convection reversal surface depends on the case. In some cases the precipitating electrons extend beyond the convection reversal surface, and in others the poleward boundary terminates at a latitude lower than the reversal surface. Previous studies suggest that the poleward boundary of the electrons having energies of a few keV is not necessarily coincident with an open/closed bounary. Thus the open/closed boundary may be at a latitude higher than the poleward boundary of the electron precipitation, or it may be at a latitude lower than the poleward boundary of the electron precipitation. We discuss relationships between the open/closed boundary and the convection reversal surface. When as a possible choice we adopt a view that the open/closed boundary agrees with the convection reversal surface, we can explain qualitatively the configuration of the B(sub y)-controlled convection on the open and close field line regions by proposing a mapping modified in accordance with IMF B(sub y).
Taguchi, S.↗
Intensive Titan exploration begins
The Cassini Orbiter spacecraft first skimmed through the tenuous upper atmosphere of Titan on 26 October 2004. This moon of Saturn is unique in our solar system, with a dense nitrogen atmosphere that is cold enough in places to rain methane, the feedstock for the atmospheric chemistry that produces hydrocarbons, nitrile compounds, and Titan's orange haze. The data returned from this flyby supply new information on the magnetic field and plasma environment around Titan, expose new facets of the dynamics and chemistry of Titan's atmosphere, and provide the first glimpses of what appears to be a complex, fluid-processed, geologically young Titan surface.
Spacecraft↗
Energetic Electron Acceleration Observed by MMS in the Vicinity of an X-Line Crossing
During the first months of observations, the Magnetospheric Multiscale Fly's Eye Energetic Particle Spectrometer instrument has observed several instances of electron acceleration up to greater than 100 keV while in the vicinity of the dayside reconnection region. While particle acceleration associated with magnetic reconnection has been seen to occur up to these energies in the tail region, it had not yet been reported at the magnetopause. This study reports on observations of electron acceleration up to hundreds of keV that were recorded on 19 September 2015 around 1000 UT, in the midst of an X-line crossing. In the region surrounding the X-line, whistler-mode and broadband electrostatic waves were observed simultaneously with the appearance of highly energetic electrons which exhibited significant energization in the perpendicular direction. The mechanisms by which particles may be accelerated via reconnection-related processes are intrinsic to understanding particle dynamics among a wide range of spatial scales and plasma environments.
Jaynes, A. N.↗
Flare Ribbon Signatures of Plasmoids
Solar flares are explosive space weather events that rapidly convert stored magnetic energy into bulk motion, plasma heating, and particle acceleration. Understanding the structure and dynamics of the magnetic reconnection that powers flares is critical for predicting the energy release. In particular, the amount of energy transferred to energetic particles is thought to be highly dependent on whether the reconnection is primarily turbulent (e.g., plasmoid dominated) or instead laminar. We present new high-resolution MHD simulations of three-dimensional reconnection in an eruptive flare and compare the results to recent data. Although flare reconnection is challenging to observe directly in the corona, highly detailed constraints on its dynamics can be obtained from observations of flare ribbons that track the chromospheric footpoints of newly reconnected field lines. The analogues of flare ribbons in our simulations are identified by tracking discontinuous changes in field-line magnetic connectivity due to the reconnection. In our highest-resolution calculations, we find that these ribbon analogues are highly structured and exhibit many ‘whorl’ patterns that are linked to turbulent plasmoids in the reconnecting current sheet. Such flare ribbon fine structure therefore reveals crucial information about the fundamental turbulent vs. laminar nature of the reconnection. Plasmoid-driven particle acceleration models would therefore predict co-location of energetic particle signatures with plasmoid-associated ribbon fine structure.
J T Dahlin↗