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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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NASA NTRS1995

Electromagnetic Components of Auroral Hiss and Lower Hybrid Waves in the Polar Magnetosphere

DE-1 has frequently observed waves in the whistler and lower hybrid frequencies range. Besides the electrostatic components, these waves also exhibit electromagnetic components. It is generally believed that these waves are excited by the electron acoustic instability and the electron-beam-driven lower hybrid instability. Because the electron acoustic and the lower hybrid waves are predominately electrostatic waves, they cannot account for the observed electromagnetic components. In this work, it is suggested that these electromagnetic components can be explained by waves that are generated near the resonance cone and that propagate away from the source. The role that these electromagnetic waves can play in particle acceleration processes at low altitude is discussed.

Wong, H. K.↗
NASA NTRS2003

Double Layers in Expanding Plasmas and Their Relevance to the Auroral Plasma Processes

When a dense plasma consisting of a cold and a sufficiently warm electron population expands, a rarefaction shock forms [Bezzerides et al., 1978]. In the expansion of the polar wind in the magnetosphere, it has been previously shown that when a sufficiently warm electron population also exists, in addition to the usual cold ionospheric one, a discontinuity forms in the electrostatic potential distribution along the magnetic field lines [Barakat and Schunk, 1984]. Despite the lack of spatial resolution and the assumption of quasi-neutrality in the polar wind models, such discontinuities have been called double layers (DLs). Recently similar discontinuities have been invoked to partly explain the auroral acceleration of electrons and ions in the upward current region [Ergun et al., 2000]. By means of one-dimensional Vlasov simulations of expanding plasmas, for the first time we make here the connection between (1) the rarefaction shocks, (2) the discontinuities in the potential distributions, and (3) DLs. We show that when plasmas expand from opposite directions into a deep density cavity with a potential drop across it and when the plasma on the high-potential side contains hot and cold electron populations, the temporal evolution of the potential and the plasma distribution generates evolving multiple double layers with an ,extended density cavity between them. One of the DLs is the rarefaction-shock (RFS) and it forms by the reflections of the cold electrons coming from the high-potential side; it supports a part of the potential drop approximately determined by the hot electron temperature. The other DLs evolve from charge separations arising either from reflection of ions coming from the low-potential side or stemming from plasma instabilities; they support the rest of the potential drop. The instabilities forming these additional double layers involve electron-ion (e-i) Buneman or ion-ion (i-i) two-stream interactions. The electron-electron two-stream interactions on the high-potential side of the RFS generate electron-acoustic waves, which evolve into electron phase-space holes. The ion population originating from the low-potential side and trapped by the RFS is energized by the e-i and i-i instabilities and it eventually precipitates into the high-potential plasma along with an electron beam. Applications of these findings to the auroral plasma physics are discussed.

Singh, Nagendra↗
NASA NTRS1990

Ion Beam Heating in the Auroral Zone

Recent satellite observations at high altitudes (greater than 5000 km) in the auroral zone have shown the existence of hybrid or bimodal ion beam distributions that are evidence of both parallel and perpendicular ion acceleration. Acceleration parallel to the magnetic field is most likely due to quasi-static electric fields (double layers) which can create outflowing ion beams; since ions of different mass will have different drift speeds due to this acceleration, a plasma configuration unstable to the ion-ion two-stream acoustic mode develops. When the net drift velocity (U) between the two ion species is greater than the sound speed (C(sub 0)), the ion-ion instability has maximum growth at oblique wave propagation. To study the nonlinear effects of the ion-ion instability in terms of plasma heating, a numerical simulation parametric study has been performed. It was found that the parallel acceleration that forms the ion beams occurs on a time scale faster than ion- ion wave growth at low drifts; thus ion-ion wave growth is expected to occur primarily for higher drift speeds (U greater than C(sub 0)) which results in strong oblique heating of the ions (both hydrogen and oxygen) forming elevated ion conics (sometimes called 'bowl' distributions). Also, strong parallel electron heating in the direction of the ion beams can occur, and electrons near the top of the acceleration region may attain a net upward drift along with the elevated ion conics. Variation of the oxygen density greatly affects the ion heating due to the ion-ion instability; as the oxygen density decreases, oxygen heating increases, in agreement with observations (Collin et al., 1987). Ion-ion electrostatic wave properties and the plasma heating that results over a wide range of auroral zone parameters are included.

Schriver, David↗
NASA NTRS1998

Relationship of Topside Ionospheric Ion Outflows to Auroral Forms and Precipitation, Plasma Waves, and Convection Observed by Polar

The POLAR satellite often observes upflowing ionospheric ions (UFIs) in and near the aurora] oval on southern perigee (approx. 5000 km altitude) passes. We present the UFI features observed by the thermal ion dynamics experiment (TIDE) and the toroidal imaging mass angle spectrograph (TIMAS) in the dusk-dawn sector under two different geomagnetic activity conditions in order to elicit their relationships with auroral forms, wave emissions, and convection pattern from additional POLAR instruments. During the active interval, the ultraviolet imager (UVI) observed a bright discrete aurora on the duskside after the substorm onset and then observed a small isolated aurora form and diffuse auroras on the dawnside during the recovery phase. The UFIs showed clear conic distributions when the plasma wave instrument (PWI) detected strong broadband wave emissions below approx. 10 kHz, while no significant auroral activities were observed by UVI. At higher latitudes, the low-energy UFI conics gradually changed to the polar wind component with decreasing intensity of the broadband emissions. V-shaped auroral kilometric radiation (AKR) signatures observed above -200 kHz by PWI coincided with the region where the discrete aurora and the UFI beams were detected. The latitude of these features was lower than that of the UFI conics. During the observations of the UFI beams and conics, the lower-frequency fluctuations observed by the electric field instrument were also enhanced, and the convection directions exhibited large fluctuations. It is evident that large electrostatic potential drops produced the precipitating electrons and discrete auroras, the UFI beams, and the AKR, which is also supported by the energetic plasma data from HYDRA. Since the intense broadband emissions were also observed with the UFIs, the ionospheric ions could be energized transversely before or during the parallel acceleration due to the potential drops.

Hirahara, M.↗
NASA NTRS1997

Relationship of Topside Ionospheric Ion Outflows to Auroral Forms and Precipitations, Plasma Waves, and Convection Observed by POLAR

The POLAR satellite often observes upflowing ionospheric ions (UFls) in and near the auroral oval on southern perigee (approximately 5000 km altitude) passes. We present the UFI features observed by the thermal ion dynamics experiment (TIDE) and the toroidal imaging mass-angle spectrograph (TIMAS) in the dusk-dawn sector under two different geomagnetic activity conditions in order to elicit their relationships with auroral forms, wave emissions, and convection pattern from additional POLAR instruments. During the active interval, the ultraviolet imager (UVI) observed a bright discrete aurora on the dusk side after the substorm onset and then observed a small isolated aurora form and diffuse auroras on the dawn side during the recovery phase. The UFls showed clear conic distributions when the plasma wave instrument (PWI) detected strong broadband wave emissions below approximately 10 kHz, while no significant auroral activities were observed by UVI. At higher latitudes, the low-energy UFI conics gradually changed to the polar wind component with decreasing intensity of the broadband emissions. V-shaped auroral kilometric radiation (AKR) signatures observed above approximately 200 kHz by PWI coincided with the region where the discrete aurora and the UFI beams were detected. The latitude of these features was lower than that of the UFI conics. During the observations of the UFI beams and conics, the lower-frequency fluctuations observed by the electric field instrument (EFI) were also enhanced, and the convection directions exhibited large fluctuations. It is evident that large electrostatic potential drops produced the precipitating electrons and discrete auroras, the UFI beams, and the AKR, which is also supported by the energetic plasma data from HYDRA. Since the intense broadband emissions were also observed with the UFIs. the ionospheric ions could be energized transversely before or during the parallel acceleration due to the potential drops.

Hirahara, M.↗
NASA NTRS2005

Space Technology 7 Disturbance Reduction System - precision control flight Validation

The NASA New Millennium Program Space Technology 7 (ST7) project will validate technology for precision spacecraft control. The Disturbance Reduction System (DRS) will be part of the European Space Agency's LISA Pathfinder project. The DRS will control the position of the spacecraft relative to a reference to an accuracy of one nanometer over time scales of several thousand seconds. To perform the control, the spacecraft will use a new colloid thruster technology. The thrusters will operate over the range of 5 to 30 micro-Newtons with precision of 0.1 micro- Newton. The thrust will be generated by using a high electric field to extract charged droplets of a conducting colloid fluid and accelerating them with a precisely adjustable voltage. The control reference will be provided by the European LISA Technology Package, which will include two nearly freefloating test masses. The test mass positions and orientations will be measured using a capacitance bridge. The test mass position and attitude will be adjustable using electrostatically applied forces and torques. The DRS will control the spacecraft position with respect to one test mass while minimizing disturbances on the second test mass. The dynamic control system will cover eighteen degrees of freedom: six for each of the test masses and six for the spacecraft. After launch in late 2009 to a low Earth orbit, the LISA Pathfinder spacecraft will be maneuvered to a halo orbit about the Earth-Sun L1 Lagrange point for operations.

microthrusters↗
NASA NTRS2019

Secondary Ion Mass Spectroscopy

Secondary Ion mass Spectroscopy (SIMS), as the name suggests, involves characterizing metallic and other materials trough the spectroscopic analysis of secondary ions emanating from the surface of the material to be characterized by the impact of the high energy primary ions. The primary ion source including the choice of its gun, voltage and current can be selected and used depending on the purpose of the analysis. In most instruments more than one primary ion gun is lined up to the sample stage and can be activated with selected accelerating parameters (voltage and beam intensity). The impingement of primary ions on to the sample surface generates positive, negative or neutral ions, electrons, atoms and atomic clusters. Majority of these sample fragments being neutral, could not be utilized as such fragments cannot be manipulated through the use of electromagnetic or electrostatic lenses. Secondary ions that are positively or negatively charged possess large variation in velocity, charge, and mass. These ionic fragments eventually travel through a system of several lenses in very high vacuum to reach detector/counter. Relative amounts of alloying elements or impurities in an alloy can be calculated from the counts of related ions accumulated in the detector/counter.

Panda, Binayak↗
NASA NTRS1989

PIC code modeling of spacecraft charging potential during electron beam injection into a background of neutral gas and plasma, part 1

Injections of nonrelativistic electron beams from an isolated equipotential conductor into a uniform background of plasma and neutral gas were simulated using a 2-D electrostatic particle code. The ionization effects on spacecraft charging are examined by including interactions of electrons with neutral gas. The simulations show that the conductor charging potential decreases with increasing neutral background density due to the production of secondary electrons near the conductor surface. In the spacecraft wake, the background electrons accelerated towards the charged spacecraft produce an enhancement of secondary electrons and ions. Simulations run for longer times indicate that the spacecraft potential is further reduced and short wavelength beam-plasma oscillations appear. The results are applied to explain the spacecraft charging potential measured during the SEPAC experiments from Spacelab 1.

Koga, J. K.↗
NASA NTRS1990

Modeling solar flare conduction fronts. I - Homogeneous plasmas and ion-acoustic turbulence. II - Inhomogeneous plasmas and ambipolar electric fields

A one-dimensional, electrostatic, particle-in-cell simulation is used here to model the expansion of a heated electron population in a coronal loop during a solar flare and the characteristics of the associated X-ray emissions. The hot electrons expand outward from the localized region, creating an ambipolar electric field which accelerates a return current of cooler, ambient electrons. Ion-acoustic waves are generated by the return currents as proposed by Brown et al. (1979), but they play little or no role in containing energetic electrons and the conduction front proposed by Brown et al. does not form. The X-ray emission efficiency of the electrons is too low in the corona for them to be the source of hard X-ray bursts. The particle dynamics changes dramatically if the heated plasma is at low altitudes and expands upward into the more tenuous plasma at higher altitudes. Two important applications of this finding are the radio-frequency heating of the corona and the collisional heating of the chromosphere by precipitating energetic electrons. In both cases, the overlying plasma has a density that is too low to supply a balancing return current to the expanding hot electrons. As a result, an ambipolar electric field develops that tends to confine the energetic electrons behind a front that propagate outward at about the speed of sound.

Mckean, M. E.↗
NASA NTRS1990

A novel sample-positioning system for microgravity application

This paper proposes a novel method for sample positioning in containerless processing at microgravity, using a system based on pulsed lasers. The method has two attributes. First, by generating beams that cancel out vectorially, the suspended material can be heated without being accelerated, a feature that can be used in melting and heat-treatment applications. Second, the specimen can be positioned within a fairly large work space. It is emphasized that this method can service a regime unfulfilled by the other levitation methods, such as electromagnetic levitation, active magnetic suspension, acoustic levitation, of electrostatic suspension.

Sridharan, G.↗
NASA NTRS2004

Cryogenic Characterization and Testing of Magnetically-Actuated Microshutter Arrays for the James Webb Space Telescope

Two-dimensional MEMS microshutter arrays (MSA) have been fabricated at the NASA Goddard Space Flight Center (GSFC) for the James Webb Space Telescope (JWST) to enable cryogenic (approximately 35 K) spectrographic astronomy measurements in the near-infrared region. Functioning as a focal plane object selection device, the MSA is a 2-D programmable aperture mask with fine resolution, high efficiency and high contrast. The MSA are close- packed silicon nitride shutters (cell size of 100 x 200 microns) patterned with a torsion flexure to allow opening to 90 degrees. A layer of magnetic material is deposited onto each shutter to permit magnetic actuation. Two electrodes are deposited, one onto each shutter and another onto the support structure side-wall, permitting electrostatic latching and 2-D addressing. New techniques were developed to test MSA under mission-similar conditions (8 K less than or equal to T less than 300K). The magnetic rotisserie has proven to be an excellent tool for rapid characterization of MSA. Tests conducted with the magnetic rotisserie method include accelerated cryogenic lifetesting of unpackaged 128 x 64 MSA and parallel measurement of the magneto-mechanical stiffness of shutters in pathfinder test samples containing multiple MSA designs. Lifetest results indicate a logarithmic failure rate out to approximately 10(exp 6) shutter actuations. These results have increased our understanding of failure mechanisms and provide a means to predict the overall reliability of MSA devices.

King, T. T.↗
NASA NTRS1984

Kinetic Alfven waves on auroral field lines

It is suggested on the basis of several observations of Alfven waves near auroral arcs that kinetic Alfven waves play a significant role in the process of particle acceleration. The characteristic properties of kinetic Alfven waves are summarized according to the theoretical classifications provided by Hasegawa and Mima (1979). The resonant coupling of large-scale surface waves to kinetic Alfven waves is also discussed. It is shown that kinetic Alfven waves can explain observations of what have previously been known as 'electrostatic' shocks.

Goertz, C. K.↗
NASA NTRS1986

Closed-drift thruster investigations

Recent data obtained from a second generation closed-drift thruster design, employing Hall current acceleration is outlined. This type device is emphasized for electric propulsion for geocentric mission applications. Because geocentric mission profiles are best achieved with a specific impulse range of 1000 to 2000 s, closed-drift thrusters are well suited for this application, permitting time payload compromises intermediate of those possible with either electrothermal or electrostatic devices. A discussion is presented of the potential advantages of using a 1000 to 2000 s device for one way orbit raising of nonpower payloads. Because closed-drift thruster operation is not space charge limited, and requires only one power circuit for steady state operation, their application is technically advantageous. Beam, plasma and thrust characteristics are detailed for a range of operating conditions.

Robinson, Raymond S.↗
NASA NTRS1992

The Solar Wind Ion Composition Spectrometer

The Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses is designed to determine uniquely the elemental and ionic-charge composition, and the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 175 km/s (protons) to 1280 km/s (Fe(8+)). The instrument, which covers an energy per charge range from 0.16 to 59.6 keV/e in about 13 min, combines an electrostatic analyzer with postacceleration, followed by a time-of-flight and energy measurement. The measurements made by SWICS will have an impact on many areas of solar and heliospheric physics, in particular providing essential and unique information on: (1) conditions and processes in the region of the corona where the solar wind is accelerated; (2) the location of the source regions of the solar wind in the corona; (3) coronal heating processes; (4) the extent and causes of variations in the composition of the solar atmosphere; (5) plasma processes in the solar wind; (6) the acceleration of energetic particles in the solar wind; (7) the thermalization and acceleration of interstellar ions in the solar wind, and their composition; and (8) the composition, charge states, and behavior of the plasma in various regions of the Jovian magnetosphere.

Gloeckler, G.↗
NASA NTRS1985

Trapping of ion conics by downward parallel electric fields

Energetic particle data from electrostatic analyzers aboard the S3-3 satellite indicative of a downward parallel electric field at low altitudes are presented to argue for a causal connection between downward parallel electric fields and ion heating. The data include observations of upward field-aligned electron beams in regions where precipitating electron fluxes are suppressed. Evidence of downward acceleration of ions and locally mirroring ion conics is also presented. It is argued that the presence of a downward electric field may have important consequences for ion conic heating and might in fact be required for the observed heating of ions to several hundred electron volts.

Gorney, D. J.↗
NASA NTRS1986

Transverse acceleration of oxygen ions by electromagnetic ion cyclotron resonance with broad band left-hand polarized waves

Central plasma sheet (CPS) ion conics are oxygen-dominated, with peak energies ranging from tens to hundreds of eV centered around pitch-angles between 115 and 130 degrees. Because of the lack of correlation between the CPS conics and the observed currents and/or electron beam-like structures, it is not likely that all of these conics are generated by interactions with electrostatic ion cyclotron waves or lower hybrid waves. Instead, it is suggested that the observed intense broad band electric field fluctuations in the frequency range between 0 and 100 Hz can be responsible for the transverse energization of the ions through cyclotron resonance heating with the left-hand polarized electromagnetic waves. This process is much more efficient for heating the oxygen ions than hydrogen ions, thus providing a plausible explanation of the oxygen dominance in CPS conics. Simple algebraic expressions are given from which estimates of conic energy and pitch angle can be easily calculated. This suggested mechanism can also provide some preheating of the oxygen ions in the boundary plasma sheet (BPS) where discrete aurorae form.

Chang, T.↗
NASA NTRS1973

Ion time-of-flight determinations of doubly to singly ionized mercury ion ratios from a mercury electron bombardment discharge

Doubly to singly charged mercury ion ratios in electron bombardment ion thruster exhaust beams have been determined as functions of bombardment discharge potential, thrust beam current, thrust beam radial position, acceleration-deceleration voltage ratio, and propellant utilization fraction. A mathematical model for two-step ionization processes has been derived, and calculated ion ratios are compared to observed ratios. Production of Hg(++) appears to result primarily from sequential ionization of Hg(+) in the discharge. Experimental and analytical results are presented, and design, construction, and operation features of an electrostatic deflection ion time-of-flight analyzer for the determination of the above-mentioned ratios are reviewed.

Sellen, J. M., Jr.↗
NASA NTRS1981

Effects of auroral-particle anisotropies and mirror forces on high-latitude electric fields

It is noted that, for most of the mechanisms for the strong electric fields that characterize the narrow regions in which there is acceleration and precipitation of ring current and/or plasma-sheet plasma, certain effects must be taken into account in simulations of auroral electric fields. The effects are those of auroral particle anisotropy, of mirror forces due to the inhomogeneous geomagnetic field, of auroral electron backscatter by the atmosphere, and of electron trapping by the combination of magnetic mirroring and electrostatic forces. What is more, the effects of the very strong perpendicular electric field must also be taken into account in a kinetic description of the Poisson equation in order to achieve a unified theory of the auroral electrostatic structure. Progress in these areas during the past few years is reviewed. It is shown that particle anisotropies and mirror forces can account for some basic electrostatic features of the quiet arc, while additional effects may be occurring in strong events in which the parallel potential drop is more than about 10 kV.

Chiu, Y. T.↗