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NASA NTRS1984

Measurements of plasma, plasma waves, and suprathermal charged particles in Saturn's inner magnetosphere

The Pioneer 11 and Voyager 1, 2 traversals of Saturn's inner magnetosphere provided direct information on the complex and highly structured distributions of plasma and suprathermal charged particles present in this region. The Voyager wave intruments also yielded absolute electron density measurements in certain inner magnetosphere locations; the wave data were used to evaluate the magnitudes of several wave-particle interactions. The plasma and wave measurements for 24-hr periods centered around closest approach, are summarized, pitch-angle scattering effects possibly associated wtih measured whistler mode turbulence are evaluated, and the effects of wave-particle interactions associated with electrostatic waves are discussed.

Scarf, F. L.↗

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 NTRS1989

Failure processes within ceramic coatings at high temperatures

Plasma sprayed coatings have a complex structure which is produced by the overlaying of many molten or semi-molten particles in the diameter range of 20 to 120 microns. The failure behavior of coatings has been characterized by using acoustic emission (AE) methodology. Coatings of NiCrAlY bond coat with a zirconia-12 wt pct yttria overlay were applied to disk-shaped specimens of U-700 alloy. A waveguide of 1-mm diameter platinum was TlG welded to the specimen and allowed it to be suspended in a tubular furnace. The specimen was thermally cycled to 1150 C and the AE monitored. Analyses have been carried out with the aim of establishing parameters which are related to the crack size population. These studies have been used to postulate types of cracking mechanisms which may occur in plasma sprayed coatings during thermal cycling. It is shown that microcracking gave rise to a large amount of AE. However, this coating still survived more thermal cycles than a coating which exhibited macrocracking events.

Berndt, Christopher↗

NASA NTRS1973

The behavior of the plasmapause at mid-latitudes: ISIS-1 Langmuir probe measurements

Observations of the electron concentration, N sub e, and temperature, T sub e, from the electrostatic probes on the ISIS-1 satellite were used to examine the location and behavior of the plasmapause at about 3000 kilometers altitude in the vicinity of L = 4. At these altitudes, the N sub e measurements are equivalent to measurements of H(+) since the satellite is well into the protonosphere. The plasmapause as is evident as a sharp drop in N sub e by a factor of 10 to 100 as the satellite passes into the polar cap, and a corresponding increase is observed as it enters the plasmasphere on the opposite side of the Earth. An enhancement of T sub e is also observed at the plasmapause, an effect that is most visible at night when the temperatures at latitudes above and below the plasmapause are usually very low. The position of the plasmapause decreases with magnetic activity but is found to be somewhat less sensitive to K sub p than is the equatorial plasmapause. Also unlike its equatorial behavior, the mid-latitude plasmapause exhibits no detectable late afternoon bulge. These differences imply rather complex coupling of the thermal plasma along the field lines that link these two regions of the plasmasphere. An additional factor may be the recently observed axial asymmetry in the geomagnetic field at high altitudes.

Brace, L. H.↗

NASA NTRS1977

NASCAP user's manual

The NASCAP (NASA Charging Analyzer Program) code simulates the charging process for a complex object in either tenuous plasma or ground test environment. Detailed specifications needed to run the code are presented. The object definition section, OBJDEF, allows the test object to be easily defined in the cubic mesh. The test object is composed of conducting sections which may be wholly or partially covered with thin dielectric coatings. The potential section, POTENT, obtains the electrostatic potential in the space surrounding the object. It uses the conjugate gradient method to solve the finite element formulation of Poisson's equation. The CHARGE section of NASCAP treats charge redistribution among the surface cells of the object as well as charging through radiation bombardment. NASCAP has facilities for extensive graphical output, including several types of object display plots, potential contour plots, space charge density contour plots, current density plots, and particle trajectory plots.

Mandell, M. J.↗

NASA NTRS1978

NASCAP user's manual, 1978

NASCAP simulates the charging process for a complex object in either tenuous plasma (geosynchronous orbit) or ground test (electron gun source) environment. Program control words, the structure of user input files, and various user options available are described in this computer programmer's user manual.

Cassidy, J. J., III↗

NASA NTRS1993

Arcjet space thrusters

Electrically powered arc jets which produce thrust at high specific impulse could provide a substantial cost reduction for orbital transfer and station keeping missions. There is currently a limited understanding of the complex, nonlinear interactions in the plasma propellant which has hindered the development of high efficiency arc jet thrusters by making it difficult to predict the effect of design changes and to interpret experimental results. A computational model developed at the University of Tennessee Space Institute (UTSI) to study laser powered thrusters and radio frequency gas heaters has been adapted to provide a tool to help understand the physical processes in arc jet thrusters. The approach is to include in the model those physical and chemical processes which appear to be important, and then to evaluate our judgement by the comparison of numerical simulations with experimental data. The results of this study have been presented at four technical conferences. The details of the work accomplished in this project are covered in the individual papers included in the appendix of this report. We present a brief description of the model covering its most important features followed by a summary of the effort.

Keefer, Dennis↗

NASA NTRS1999

Rocket/Radar Sporadic-E Experiment Conducted during the El Coqui 2 Campaign

In order to investigate the complex electrodynamics and neutral-plasma coupling inherent to sporadic-E layers in the earth's mid-latitude ionosphere, a series of rocket/radar experiments were planned as part of the NASA El Coqui H Campaign from Tortuguero Launch Range, Puerto Rico, in March-April, 1998. The rocket experiments consisted of two pairs of "mother-daughter" payloads with limited apogees so that the payloads "hovered" in the sporadic-E region (95-125 km). Each payload pair included vector DC and AC electric field detectors, a highly accurate flux-gate DC magnetometer, an ion mass spectrometer, an ionization gauge, and spaced-electric field receivers to measure the wavelength and phase velocity of the unstable plasma waves. Separate rockets were included to simultaneously carry aloft TMA trails to measure the neutral wind and its velocity shear, believed responsible for the sporadic-E layer formation. In addition to the rocket experiments, incoherent scatter radar measurements of plasma density and drift velocity were gathered almost every night during the 3 week campaign. Continuous VHF backscatter radar operations were carried out from a site near Salinas, Puerto Rico, where 3-m backscatter echoes were observed associated with sporadic-E and other types of low altitude ionospheric layers. Other radars that operated during the campaign included an HF backscatter system near Ponce, Puerto Rico, and a second VHF backscatter radar set up near Aguadila Puerto Rico. On 24 March 1998, one of the instrumented rockets was launched, attaining an apogee of 129 km. The payloads successfully pierced an intense sporadic-E layer observed by both the Arecibo radar and the in-situ density and ion mass spectrometer probes. In-situ DC electric fields revealed very low (about 1-2 mV/m) ambient fields with small amplitude structures of the same order. No high frequency (short scale) waves were observed, consistent with the VHF backscatter observations at the time of the launch. An overview of the observations will be presented.

Pfaff, R.F.↗

NASA NTRS2011

Shuttle Communications and Tracking, Avionics, and Electromagnetic Compatibility

By definition, electromagnetic compatibility (EMC) is the capability of components, sub-systems, and systems, to operate in their intended electromagnetic environment, within an established margin of safety, and at design levels of performance. Practice of the discipline itself incorporates knowledge of various aspects of applied physics, materials science, and engineering across the board, and includes control and mitigation of undesirable electromagnetic interaction between intentional and unintentional emitters and receivers of radio frequency energy, both within and external to the vehicle; identification and control of the hazards of non-ionizing electromagnetic radiation to personnel, ordnance, and fuels and propellants; and vehicle and system protection from the direct and indirect effects of lightning and various other forms of electrostatic discharge (ESD) threats, such as triboelectrification and plasma charging. EMC is extremely complex and far-reaching, affecting in some degree every aspect of the vehicle s design and operation. The most successful efforts incorporate EMC design features and techniques throughout design and fabrication of the vehicle s structure and components, as well as appropriate operational considerations with regard to electromagnetic threats in the operational environment, from the beginning of the design effort to the end of the life cycle of the manufactured product. This approach yields the highest design performance with the lowest cost and schedule impact.

deSilva, K.↗

NASA NTRS2015

Suzaku Observation of the Classical Nova V2491 Cyg in Quiescence

We present Suzaku XIS observation of V2491 Cyg (Nova Cyg 2008 No. 2) obtained in quiescence, more than two years after the outburst. The nova was detected as a very luminous source in a wide spectral range from soft to hard X-rays. A very soft blackbody-like component peaking at 0.5 keV indicates that either we observe remaining, localized hydrogen burning on the surface of the white dwarf, or accretion onto a magnetized polar cap. In the second case, V2491 Cyg is a candidate "soft intermediate polar". We obtained the best fit for the X-ray spectra with several components: two of thermal plasma, a blackbody and a complex absorber. The later is typical of intermediate polars. The X-ray light-curve shows a modulation with an approximately 38 min period. The amplitude of this modulation is strongly energy dependent and reaches maximum in the 0.8-2.0 keV range. We discuss the origin of the X-ray emission and pulsations, and the likelihood of the intermediate polar scenario.

cataclysmic variables: general aEuro" nova: indivi↗

NASA NTRS1977

Ray trajectories in a torus: An application of MACSYMA to a complex numerical computation

The study of ray trajectories of plasma waves in a torodial geometry using MACSYMA is an example of how symbolic, numerical, and graphical facilities can be used in concert to accomplish a complex computational goal. Computational features of this study which are of particular significance include: the derivation of code (i.e. writing functions to generate program fragments), the use of array functions to simplify the specification of a numerical iteration scheme, and the graphical presentation of the results. Mathematically, this study originates in the solution of a linear inhomogeneous partial differential equation in 3 dimensions by the method of characteristics. While it is possible to describe this equation compactly by using vector notation, and by specifying the spatial variation of the coefficients in terms of intermediate parameters, the transformation of the equation into a form amenable to solution is very tedious. A MACSYMA program is presented for obtaining description of the rf field structure excited by a waveguide located at the edge of a toroidal plasma confinement device.

Kulp, J. L.↗

NASA NTRS2004

Self-Organized Criticality, Multifractals, and Intermittent Turbulence in Earth's Magnetotail

We have achieved all the goals stated in our grant proposal in collaboration with Dr. C.C. Wu of the University of California at Los Angeles. Specifically, these include: The understanding of the complexity induced nonlinear spatiotemporal structures and the coexisting propagating modes. The development of plasma resonances and coherent structures in space plasmas. The study of fluctuation-induced nonlinear instabilities and their role in the reconfiguration of magnetic topologies in the magnetotail. The development of "anisotropic three-dimensional complexity" in the plasma sheet due to localized merging and interactions of the magnetic coherent structures and associated topological phase transitions. The understanding of the intermittent turbulence and energization process of the observed Bursty Bulk Flows (BBF's) in the Earth s magnetotail. The acceleration of ions due to the intermittent turbulence of propagating arid nonpropagating fluctuations In the following, we include lists of our published papers, invited talks, and professional activities. A detailed description of our accomplished research results is given in Section IV.

Chang, Tom↗

NASA NTRS2000

Simulation and Experimental Measurements of Inductively Coupled CF4 and CF4/Ar Plasmas

The recently developed code SEMS (semiconductor equipment modeling software)is applied to the simulation of CF4 and CF4/Ar inductively coupled plasmas (ICP). This work builds upon the earlier nitrogen, transformer coupled plasma (TCP) SEMS research by demonstrating its accuracy for more complex reactive mixtures, moving closer to the realization of a virtual plasma reactor. Attention is given to the etching of and/or formation of carbonaceous films on the quartz dielectric window and diagnostic aperatures. The simulations are validated through comparisons with experimental measurements using FTIR (Fourier Transform Infrared) and UV absorption spectroscopy for CFx and SiFx neutral radicals, QMS (quadrupole mass spectrometry) for the ions, and Langmuir probe measurements of electron number density and temperature in an ICP GEC reference cell.

Hash, D. B.↗

NASA NTRS2008

Flare Plasma Iron Abundance

The equivalent width of the iron-line complex at 6.7 keV seen in flare X-ray spectra suggests that the iron abundance of the hottest plasma at temperatures >approx.10 MK may sometimes be significantly lower than the nominal coronal abundance of four times the photospheric value that is commonly assumed. This conclusion is based on X-ray spectral observations of several flares seen in common with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Solar X-ray Spectrometer (SOXS) on the second Indian geostationary satellite, GSAT-2. The implications of this will be discussed as it relates to the origin of the hot flare plasma - either plasma already in the corona that is directly heated during the flare energy release process or chromospheric plasma that is heated by flare-accelerated particles and driven up into the corona. Other possible explanations of lower-than-expected equivalent widths of the iron-line complex will also be discussed.

Dennis, Brian R.↗

NASA NTRS2012

Comparison of Observations of Sporadic-E Layers in the Nighttime and Daytime Mid-Latitude Ionosphere

A comparison of numerous rocket experiments to investigate mid-latitude sporadic-E layers is presented. Electric field and plasma density data gathered on sounding rockets launched in the presence of sporadic-E layers and QP radar echoes reveal a complex electrodynamics including both DC parameters and plasma waves detected over a large range of scales. We show both DC and wave electric fields and discuss their relationship to intense sporadic-E layers in both nighttime and daytime conditions. Where available, neutral wind observations provide the complete electrodynamic picture revealing an essential source of free energy that both sets up the layers and drives them unstable. Electric field data from the nighttime experiments reveal the presence of km-scale waves as well as well-defined packets of broadband (10's of meters to meters) irregularities. What is surprising is that in both the nighttime and daytime experiments, neither the large scale nor short scale waves appear to be distinctly organized by the sporadic-E density layer itself. The observations are discussed in the context of current theories regarding sporadic-E layer generation and quasi-periodic echoes.

Pfaff, R.↗

NASA NTRS2005

Dusty-Plasma Particle Accelerator

A dusty-plasma apparatus is being investigated as means of accelerating nanometer- and micrometer-sized particles. Applications for the dusty-plasma particle accelerators fall into two classes: Simulation of a variety of rapidly moving dust particles and micrometeoroids in outer-space environments that include micrometeoroid streams, comet tails, planetary rings, and nebulae and Deposition or implantation of nanoparticles on substrates for diverse industrial purposes that could include hardening, increasing thermal insulation, altering optical properties, and/or increasing permittivities of substrate materials. Relative to prior apparatuses used for similar applications, dusty-plasma particle accelerators offer such potential advantages as smaller size, lower cost, less complexity, and increased particle flux densities. A dusty-plasma particle accelerator exploits the fact that an isolated particle immersed in plasma acquires a net electric charge that depends on the relative mobilities of electrons and ions. Typically, a particle that is immersed in a low-temperature, partially ionized gas, wherein the average kinetic energy of electrons exceeds that of ions, causes the particle to become negatively charged. The particle can then be accelerated by applying an appropriate electric field. A dusty-plasma particle accelerator (see figure) includes a plasma source such as a radio-frequency induction discharge apparatus containing (1) a shallow cup with a biasable electrode to hold the particles to be accelerated and (2) a holder for the substrate on which the particles are to impinge. Depending on the specific design, a pair of electrostatic-acceleration grids between the substrate and discharge plasma can be used to both collimate and further accelerate particles exiting the particle holder. Once exposed to the discharge plasma, the particles in the cup quickly acquire a negative charge. Application of a negative voltage pulse to the biasable electrode results in the initiation of a low-current, high-voltage cathode spot. Plasma pressure associated with the cathode spot as well as the large voltage drop at the cathode spot accelerates the charged particles toward the substrate. The ultimate kinetic energy attained by particles exiting the particle holder depends in part on the magnitude of the cathode spot sheath potential difference, which is proportional to the magnitude of the voltage pulse, and the on the electric charge on the dust. The magnitude of the voltage pulse can be controlled directly, whereas the particle s electric charge can be controlled indirectly by controlling the operating parameters of the plasma apparatus.

Foster, John E.↗

NASA NTRS1994

Analysis of plasma measurements for the Geotail mission

Data processing and research efforts for the period October 1993 to September 1994 are reported. Routine data processing includes the production of color spectrograms and computing of quantitative plasma parameters such as the plasma number density, bulk flow velocity, temperature, and pressure. In addition, specialized analysis software is being developed for specific and general applications. Research activities include the measurement of plasmas from the Geotail spacecraft; the processing of the measurements from a hot plasma analyzer to compute one minute averages of plasma densities, temperatures, and velocities for a substantial part of the Geotail deep tail mission; and, a preliminary survey of the magnetotail for geocentric radial distances of 10 to 210 earth radii. The topology of the magnetotail with its various regions and boundaries is determined by a complex interaction with the fields and plasmas of the solar wind. Observations of the rotation of the magnetic field in the solar wind show that it is well correlated with repeated transitions at Geotail from the magnetotail lobe to a magnetosheath-like boundary layer.

Frank, Louis A.↗

NASA NTRS2014

Correlation of ISS Electric Potential Variations with Mission Operations

Spacecraft charging on the International Space Station (ISS) is caused by a complex mix of the low Earth orbit plasma environment, space weather events, operations of the high voltage solar arrays, and changes in the ISS configuration and orbit parameters. Measurements of the ionospheric electron density and temperature along the ISS orbit and variations in the ISS electric potential are obtained from the Floating Potential Measurement Unit (FPMU) suite of four plasma instruments (two Langmuir probes, a Floating Potential Probe, and a Plasma Impedance Probe) on the ISS. These instruments provide a unique capability for monitoring the response of the ISS electric potential to variations in the space environment, changes in vehicle configuration, and operational solar array power manipulation. In particular, rapid variations in ISS potential during solar array operations on time scales of tens of milliseconds can be monitored due to the 128 Hz sample rate of the Floating Potential Probe providing an interesting insight into high voltage solar array interaction with the space plasma environment. Comparing the FPMU data with the ISS operations timeline and solar array data provides a means for correlating some of the more complex and interesting ISS electric potential variations with mission operations. In addition, recent extensions and improvements to the ISS data downlink capabilities have allowed more operating time for the FPMU than ever before. The FPMU was operated for over 200 days in 2013 resulting in the largest data set ever recorded in a single year for the ISS. This presentation will provide examples of a number of the more interesting ISS charging events observed during the 2013 operations including examples of rapid charging events due to solar array power operations, auroral charging events, and other charging behavior related to ISS mission operations.

Willis, Emily M.↗