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Dipole antenna radiation in compressible anisotropic electron plasma overlying imperfectly conducting half space, evaluating Fourier- Bessel integrals for lunar environment
Evaluation of data from the 14.5- and 30-kHz plasma-wave detector channels aboard Ogo 5 for the period Dec. 2, 1968, to Apr. 8, 1969, demonstrating the relatively isotropic occurrence of electron plasma oscillations upstream from the bow shock. These plasma oscillations were shown previously to correlate with streams of electrons having energy greater than 700 eV. The present study implies the presence of such streams, most probably electrons reflected by the bow shock, irrespective of spacecraft longitude in the upstream solar wind.
Dipole antenna radiation in compressible anisotropic electron plasma overlying imperfectly conducting half space, solving for lunar environment
Two nightside encounters with Mercury's magnetosphere by Mariner 10 revealed bow shock and magnetosheath signatures in the plasma electron data that are entirely consistent with the geometry expected for an interaction between a planet-centered magnetic dipole and the solar wind. The geometrically determined distance between the planet's center and the solar wind stagnation point is 1.4 plus or minus 0.1 R sub M. Both diffuse and sharp shock crossings were observed on the two magnetosphere encounters.
ISEE-3 electric field measurements are used to examine the properties of electromagnetic continuum radiation in the distant geomagnetic tail. Continuum is observed in all the tail's plasma regions and in the magnetosheath. The power spectrum at 210 R sub E is nearly identical to that at 40 R sub E, indicating that the tail cavity forms a reasonably loss-free waveguide. The angular distribution exhibits both anisotropy, which is similar to that observed nearer the earth, and isotropy for high frequencies (greater than 31.6 kHz) in the magnetosheath and for low frequencies (equal to or less than 17.8 kHz) in the tail lobes and boundary layer. Isotropic radiation suggests that, in addition to the near earth source, continuum is also generated over a large spatial region in the tail. Electrostatic electron plasma oscillations are also detected in the distant tail, and these could represent the local source of the continuum.
Propagation of an electron beam through a gas creates a secondary electron/ion plasma which can have subsequent deleterious effects on the propagation of the beam. In the case of pulsed electron beams with short micropulse durations, these effects can be greatly reduced through the use of a small doping fraction of an electron attachment gas. We present a model which allows the calculation of the reduction in unbound plasma electron density attainable with a gaseous dielectric dopant. Potential problems with a dopant, including increased ionization, increased scattering, altered refractive index, and dopant saturation and fragmentation, are discussed.
Solar wind electron component detection by plasma experiment on Pioneer 6, particularly class 2B flare and quiet period
Electrostatic waves are observed around the plasma frequency fpe in the electron foreshock, together with electrons backstreaming from the bow shock. Using data from the sounder aboard ISEE 1, it is shown that this noise, previously understood as narrow band Langmuir waves more or less widened by Doppler shift or nonlinear effects, is in fact composed of two distinct parts: one is a narrow band noise, emitted just above fpe, and observed at the upstream boundary of the electron foreshock. This component has been interpreted as Langmuir waves emitted by a beam-plasma instability. It is suggested that it is of sufficiently large amplitude and monochromatic enough to trap resonant electrons. The other is a broad band noise, more impulsive than the narrow band noise, observed well above and/or well below fpe, deeper in the electron foreshock. The broad band noise has an average spectrum with a typical bi-exponential shape; its peak frequency is not exactly equal to fpe and depends on the Deybe length. This peak frequency also depends on the velocity for which the electron distribution has maximum skew. An experimental determination of the dispersion relation of the broad band noise shows that this noise, as well as the narrow band noise, may be due to the instability of a hot beam in a plasma.
Two plasma regimes were observed in the Venus wake, one characterized by negative-going anisotropies accompanied by high bulk speeds and low magnetic variance, and the other characterized by positive-going anisotropies accompanied by low bulk speeds and high magnetic variance. The two modes alternate in time in a stochastic bimodal fashion as interplanetary magnetic field discontinuities propagate past Venus and switch on the positive anisotropies. The positive mode probably represents enhanced planetary ion pickup which results in instabilities, the damping of which energizes the electrons in the distant wake.
The three-dimensional electron spectrometer of the Reme plasma analyzer-complete positive ion, electron and ram negative ion measurements near comet Halley (RPA-COPERNIC) experiment aboard the Giotto spacecraft, although damaged during the comet Halley encounter in March 1986, has provided very new results during the encounter on July 10, 1992, with the weakly active comet Grigg-Skjellerup (G-S). The main characteristic features of the highly structured interaction region extending from approximately 26,500 km inbound to approximately 37,200 km outbound are presented. These results are compared to the results obtained by the same instrument during the Giotto comet Halley fly-by. Despite the large difference in the size of the interaction regions (approximately 60,000 km for G-S, approximately 2000,000 km for Halley) due to 2 orders of magnitude difference in cometary neutral gas production rate, there are striking similarities in the solar wind interactions with the two comets.
Comparing results of reentry plasma diagnostic experiment at 25,000 ft/sec with flow-field values at four locations on spacecraft
Initial results are presented from the electron measurements made by the Ames Research Center Plasma Analyzer during the inbound passage of Pioneer 10 in the vicinity of Jupiter. The observations indicate that as in the case of the earth's magnetosheath, there is an increase in electron temperature across the Jovian bow shock. During the second extended magnetosheath traversal (approximately 54 to 46.5 Jupiter radii) the electron temperatures were generally higher than those observed during the first magnetosheath traversal (109 to 96 Jupiter radii). These higher electron temperatures are in agreement with the measured higher magnitude of the magnetic field and ion density during this traversal. These observations are consistent with the contraction of the Jovian magnetosphere due to an increase in the solar wind dynamic pressure.
Selected events of plasma wave and electromagnetic emissions in the earth's electron fore-shock region have been studied. Strong emissions are observed in the plasma-wave band when the site of the satellite is magnetically connected to the bow shock. These emissions are generally highly fluctuating. Under certain conditions one observes electromagnetic radiation at the second harmonic produced locally. Electromagnetic emission generated at a position far away from the site of the spacecraft is occasionally detected giving rise to remote sensing of the bow shock. These emissions are related to energetic electron fluxes.
Since 1960, the Arc Jet Complex at NASA Ames Research Center has been a source of long-duration, high-enthalpy flow for materials testing with application to the thermal protection of aerospace vehicle components. From their inception the facilities have played an integral role supporting many of NASA's space flight programs and numerous DoD projects. In recent years advancements in computational fluid dynamics (CFO) have made the resultant models a valuable tool for assessing and predicting performance, however, the inherent limitation of models to compensate for a dissociated, transitionally high temperature nonequilibrated flowfield have made further measurements necessary. The use of electrostatic probe diagnostics within similarly harsh plasma environments in previous studies have been met with much success. In this study, the use of a single Langmuir probe was implemented to characterize the plasma parameters of interest as they vary radially within a large volume of the plume. Classical Langmuir probe theory was applied to achieve first order estimates of the heavy particle temperature, the ratio T(sub i)/T(sub e), and the ionization fraction. As expected, both the electron temperature and electron density measurements show a dependence on radial distance from the plume centerline, with electron density profiles showing the largest dependence. This paper aims to validate and strengthen modeling work conducted at the NASA Ames Research Center by measuring the critical plasma parameters (electron temperature, electron density, and plasma potential) within the arc plume of a subscale arc jet. These parameters are intended to give physical insight into the flow characteristics while providing the necessary boundary conditions to validate full scale simulations.
Examination of electron spectra obtained during inbound transversal of the outer Jovian magnetosphere shows a consistent peak near 4 eV where the thermal component of magnetospheric electrons is observed, corresponding to a temperature of about 50,000 K. The existence of a high beta plasma is inferred on the basis of electron and magnetic field measurements, assuming equilibrium between ions and electrons and pressure balance across the magnetophase. Observations imply the existence of thermal plasma in the outer magnetosphere which may be responsible for large-scale inflation of the outer magnetic field. It is concluded that ambient thermal plasma and photoelectrons in the outer magnetosphere will likely prevent charge buildup in spacecraft, but that it remains a possibility in the inner magnetosphere, where thermal electron measurements are obscured by high background.
The observation of three distinct components of the electron distribution function measured in the intermediate ionized coma (IIC) and plasma tail of Comet Giacobini-Zinner is reported. It is believed that the cold component represents electrons produced close to the comet nucleus by ionization of cometary matter and subsequent cooling by Coulomb collisions. The second component also appears to be composed of electrons produced by photoionization of cometary neutrals, but sufficiently far from the nucleus that the distributions are largely unaffected by Coulomb interactions. The hot component is probably a population of electrons originating in the solar wind. Throughout the IIC, the electrostatic potential of the spacecraft was very low (less than 0.8 eV), implying that ICE generated very little impact-produced plasma during its passage.
The JPL Workshop addressed a number of plasma issues that bear on advanced spaceborne technology for the years 2000 and beyond. Primary interest was on the permanently manned space station with a focus on identifying environmentally related issues requiring early clarification by spaceborne plasma experimentation. The Beams Working Group focused on environmentally related threats that platform operations could have on the conduct and integrity of spaceborne beam experiments and vice versa. Considerations were to include particle beams and plumes. For purposes of definition it was agreed that the term particle beams described a directed flow of charged or neutral particles allowing single-particle trajectories to represent the characteristics of the beam and its propagation. On the other hand, the word plume was adopted to describe a multidimensional flow (or expansion) of a plasma or neutral gas cloud. Within the framework of these definitions, experiment categories included: (1) Neutral- and charged-particle beam propagation, with considerations extending to high powers and currents. (2) Evolution and dynamics of naturally occurring and man-made plasma and neutral gas clouds. In both categories, scientific interest focused on interactions with the ambient geoplasma and the evolution of particle densities, energy distribution functions, waves, and fields.
During November-December 1991, the International Cometary Explorer (ICE) and Ulysses spacecraft were aligned in solar longitude, with an angular offset as small as 1 deg and a radial offset of 3.8 to 4.0 AU. Both spacecraft carry spectrometers which measure the thermal and suprathermal solar wind electron distributions. During the alignment interval, both spacecraft encountered the declining phase of a high-speed solar wind stream, representing unshocked plasma. We use the aligned observations from ICE and Ulysses to characterized the radial gradients in core and halo electron temperature, relative halo density, and heat flux, as well as the core and total polytropic indices. The thermal properties of the core vary widely in a range from isothermal to adiabatic, while the halo is more nearly isothermal. The halo density falls off more steeply for higher density plasma, and the electron heat flux gradient indicates constant or decreasing distribution skewness.