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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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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Negative ions from alkali hydrides as a source for H(-) beams

The production of H(-) ions by heating LiH powder in a high-temperature crucible was investigated experimentally and theoretically. It is found that the efficiency of H(-) ion production by this method is high. However, the theory for the negative surface ionization indicates that such high efficiency is not possible at crucible temperatures of about 750 C. The need for a further study of LiH ionization is emphasized.

Srivastava, S. K.↗
NASA NTRS1986

A study of target heating in low-energy ion-beam processing

A bonded thermocouple approach is employed to accurately determine semiconductor surface heating profiles as a function of energy, position, and gas species in a high-current low-energy ion beam etching system. The total beam current is kept at 200 mA and the extractor voltage at 300 V. It is found that the ionic species, the radial position in the ion beam, and the kinetic energy of the ions, all of which effect the ion current density, must be taken into account in recording the temperature rise of the bombarded surface. It is also noted that the occurrence of this temperature rise is dependent on the thermal contacts and heat sinking.

Ringel, S. A.↗
NASA NTRS2017

Thermal Radiation Anomalies Associated with Major Earthquakes

Recent developments of remote sensing methods for Earth satellite data analysis contribute to our understanding of earthquake related thermal anomalies. It was realized that the thermal heat fluxes over areas of earthquake preparation is a result of air ionization by radon (and other gases) and consequent water vapor condensation on newly formed ions. Latent heat (LH) is released as a result of this process and leads to the formation of local thermal radiation anomalies (TRA) known as OLR (outgoing Longwave radiation, Ouzounov et al, 2007). We compare the LH energy, obtained by integrating surface latent heat flux (SLHF) over the area and time with released energies associated with these events. Extended studies of the TRA using the data from the most recent major earthquakes allowed establishing the main morphological features. It was also established that the TRA are the part of more complex chain of the short-term pre-earthquake generation, which is explained within the framework of a lithosphere-atmosphere coupling processes.

Ouzounov, Dimitar↗
NASA NTRSDate not supplied

Thermal radiation effects in the atmosphere initiated by pre-earthquake processes

The science community is still looking for pre-earthquake indicators of major seismic events in order to minimize the loss of human life. Recent advances in satellite technology have helped to increase the scientific understanding of the nature of pre-earthquake phenomena in the atmosphere and their relationship with transitional thermal anomalies. It was realized that the thermal heat fluxes over areas of earthquake preparation are a result of air ionization by Rn222, its isotopes and progenies and consequent water vapor condensation on newly formed ions. Latent heat (LH) is released as a result of this process and leads to the formation of local thermal radiation anomalies (TRA) known as outgoing longwave radiation (OLR). We recorded data from the most recent major earthquakes in California (2014) Nepal (2015) that allowed us to summaries TRA's main morphological features. It was also established that the TRA is part of a more complex chain of the short‐term earthquake precursors, which are explained within the framework of a Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) model.

Dimitar Ouzounov↗
NASA NTRS2016

Growth and Saturation of Ion Acoustic Waves in Hall Thrusters

In this paper we present for the first time a conjecture that the electron transport in Hall thrusters is controlled by ion acoustic waves in two distinct ion populations. The first, and largest population, is the main beam, an ion fluid generated upstream of the Acceleration Region. These ions experience electrons with largest ExB drift, but because beam ions have been heated during the ionization process, Landau damping limits the growth of ion acoustic waves. The second population is composed of ions generated at low potentials farther downstream that don’t thermalize with the fast moving ion beam. The existence of this separate population has been recognized for decades as the source of the high angle ions in Hall thruster plumes. Because these ions aren’t heated and have velocities much different from main beam ions, the amplitude of ion acoustic waves in this population is not Landau damped and grows to saturation. Scattering from these waves reduces the Hall parameter in the near plume where slow ions make up a significant fraction of the population.

Katz, Ira↗
NASA NTRS1989

Excitation of low-frequency waves by auroral electron beams

The electron distribution functions measured by the Dynamics Explorer 1 satellite during an auroral pass in 1981 are used in a linear instability analysis of low-frequency electromagnetic and electrostatic waves near and below the hydrogen gyrofrequency. It is suggested that the low-frequency electric and magnetic noise in the auroral zone might be explained by O and H electromagnetic ion cyclotron waves excited by energetic electron beams. An instability analysis suggests that upward and downward streaming electrons throughout the central plasma sheet region provide the free energy for heating oxygen ion through oxygen electrostatic ion cyclotron waves.

Lin, C. S.↗
NASA NTRS1994

Loop heating by D.C. electric current and electromagnetic wave emissions simulated by 3-D EM particle zone

We have shown that a current-carrying plasma loop can be heated by magnetic pinch driven by the pressure imbalance between inside and outside the loop, using a 3-dimensional electromagnetic (EM) particle code. Both electrons and ions in the loop can be heated in the direction perpendicular to the ambient magnetic field, therefore the perpendicular temperature can be increased about 10 times compared with the parallel temperature. This temperature anisotropy produced by the magnetic pinch heating can induce a plasma instability, by which high-frequency electromagnetic waves can be excited. The plasma current which is enhanced by the magnetic pinch can also excite a kinetic kink instability, which can heat ions perpendicular to the magnetic field. The heating mechanism of ions as well as the electromagnetic emission could be important for an understanding of the coronal loop heating and the electromagnetic wave emissions from active coronal regions.

Sakai, J. I.↗
NASA NTRS1992

Wave-particle interaction at the plasmasphere-ring current interface

During the plasmasphere filling process following geomagnetic storms, an outward density decrease of the cold plasma at L = 3-4 is typically observed. When this structure overlaps with the sharp inner edge of the ring current, wave activity is detected at linearly stable phase velocities. The excitation of these waves around the lower hybrid frequency and their effects on the heating of thermal ions is analyzed. It is found that lower hybrid drift waves are most effective at heating lower mass ions, e.g. plasmaspheric H(+), versus He(+), which may be heated more effectively by electromagnetic ion cyclotron waves driven unstable by the ring current loss cone.

Roth, Ilan↗
NASA NTRS1982

On the preferential acceleration and heating of solar wind heavy ions

The feasibility of producing the observed velocities and temperatures of solar wind heavy ions by the resonant cyclotron interaction with left-polarized hydromagnetic waves was investigated. A "most favorable case" scenario in which the waves are parallel-propagating and dispersionless and the energy for the wave acceleration and heating is taken from saturated low-frequency Alfven waves via a cascade to higher frequencies, is incorporated into a numerical solar wind code and agreement with observation is tested. The resonant cyclotron interaction is shown to fail on at least three points, even in this most favorable case.

Isenberg, P. A.↗
NASA NTRS2022

Seasonal Variation of Thermospheric Composition Observed by NASA GOLD

We examine characteristics of the seasonal variation of thermospheric composition using column number density ratio ∑O/N(2) observed by the NASA Global Observations of Limb and Disk (GOLD) mission from low-mid to mid-high latitudes. We also use ∑O/N(2) derived from the Global Ultraviolet Imager (GUVI) limb measurements onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite and estimated by the NRLMSISE-00 empirical model to aid our investigation. We found that the ∑O/N(2) seasonal variation is hemispherically asymmetric: in the southern hemisphere, it exhibits the well-known annual and semiannual pattern, with highs near the equinoxes, and primary and secondary lows near the solstices. In the northern hemisphere, it is dominated by an annual variation, with a minor semiannual component with the highs shifting toward the wintertime. We also found that the durations of the December and June solstice seasons in terms of ∑O/N(2) are highly variable with longitude. Our hypothesis is that ion-neutral collisional heating in the equatorial ionization anomaly region, ion drag, and auroral Joule heating play substantial roles in this longitudinal dependency. Finally, the rate of change in ∑O/N(2) from one solstice season to the other is dependent on latitude, with more dramatic changes at higher latitudes.

thermosphere↗
NASA NTRS1981

Monte Carlo simulation of charged particles upstream of the earth's bow shock

A simple model of the earth's bow shock is presented and compared with ISEE-1 observations of diffuse ions upstream of the shock. Ion behavior is modeled in a test particle simulation using Monte Carlo techniques for a plane parallel shock at which cold solar wind ions are heated sufficiently to allow diffusion back upstream. Fitting of the model to the observations indicates that the diffusion coefficient must increase faster than linearly with velocity, and provides an upper limit to the acceleration efficiency defined as the proportion of incoming solar wind ions accelerated and observed upstream. Results suggest that astrophysical shocks are capable of accelerating ions directly from the thermal plasma without the need for a distinct preenergizing injection stage.

Ellison, D. C.↗
NASA NTRS1989

Molecule formation and infrared emission in fast interstellar shocks. III - Results for J shocks in molecular clouds

The structure and emission spectrum of J shocks in molecular gas are studied over a broad range of conditions. It is found that at high densities chemistry has a profound effect on the emission spectrum: the density behind the shock is sufficiently high that some of the internal energy of the newly formed H2 molecules is transformed to the gas as heat by collisional deexcitations, producing the H2 formation plateau. In this temperature plateau, endothermal reactions and neutral-neutral chemical reactions with activation energies can proceed efficiently, producing significant quantities of warm H2, CO, OH, and H2O and enhanced columns of warm atoms and ions. The heat generated by the H2 formation is radiated in collisionally excited atomic fine-structure lines.

Hollenbach, David↗
NASA NTRS2000

Neural network recognition of chemical class information in mobility spectra obtained at high temperatures

A minimal neural network was applied to a large library of high-temperature mobility spectra drawn from 16 chemical classes including 154 substances with 2000 spectra at various concentrations. A genetic algorithm was used to create a representative subset of points from the mobility spectrum as input to a cascade-type back-propagation network. This network demonstrated that significant information specific to chemical class was located in the spectral region near the reactant ions. This network failed to generalize the solution to unfamiliar compounds necessitating the use of complete spectra in network processing. An extended back-propagation network classified unfamiliar chemicals by functional group with a mean for average values of 0.83 without sulfides and 0.79 with sulfides. Further experiments confirmed that chemical class information was resident in the spectral region near the reactant ions. Deconvolution of spectra demonstrated the presence of ions, merged with the reactant ion peaks that originated from introduced samples. The ability of the neural network to generalize the solution to unfamiliar compounds suggests that these ions are distinct and class specific.

NASA Discipline Environmental Health↗
NASA NTRS1987

Increase of ion kinetic temperature across a collisionless shock. II - A simulation study

The present paper is a continuation of the preceding article by Lee et al., (1986) in which it is suggested that the nonadiabatic motion of the directly transmitted ions in a quasi-perpendicular shock wave can result in an increase of the ion kinetic temperature transverse to the ambient magnetic field in the downstream. A series of computer simulations based on a hybrid code have been carried out to examine the dynamics of the transmitted ions in both the subcritical and supercritical shock waves. It is found that, in both cases, the directly transmitted ions can contribute to the heating process. In the case of a resistiveless supercritical shock, the reflected and transmitted ions can be equally important; whereas for a subcritical shock, the transmitted ions are primarily responsible for the ion heating.

Lee, L. C.↗
NASA NTRS2009

Coronal Holes

This paper reviews measurements of the plasma properties in coronal holes and how these measurements are used to reveal details about the physical processes that heat the solar corona and accelerate the solar wind. Evidence is presented for both heating and acceleration of the solar wind by open flux tubes energized by footpoint-driven wave-like fluctuations, and for intermittent energy deposition from closed loops into the open-field regions. Special emphasis is given to spectroscopic and coronagraphic measurements that allow the highly dynamic nonequilibrium evolution of the plasma to be followed as the asymptotic conditions in interplanetary space are established in the extended corona. For example, the importance of kinetic plasma physics and turbulence in coronal holes has been affirmed by surprising measurements from the UVCS instrument on SOHO that heavy ions are heated to hundreds of times the temperatures of protons and electrons. These observations point to specific kinds of collisionless Alfven wave damping (i.e., ion cyclotron resonance). Despite our incomplete knowledge of the complex multi-scale plasma physics, much progress has been made toward the goal of understanding the physical processes ultimately responsible for producing the observed properties of coronal holes.

Cranmer, Steven R.↗
NASA NTRS1985

Prompt acceleration of ions by oblique turbulent shocks in solar flares

Solar flares often accelerate ions and electrons to relativistic energies. The details of the acceleration process are not well understood, but until recently the main trend was to divide the acceleration process into two phases. During the first phase elctrons and ions are heated and accelerated up to several hundreds of keV simultaneously with the energy release. These mildly relativistic electrons interact with the ambient plasma and magnetic fields and generate hard X-ray and radio radiation. The second phase, usually delayed from the first by several minutes, is responsible for accelerating ions and electrons to relativistic energies. Relativistic electrons and ions interact with the solar atmosphere or escape from the Sun and generate gamma ray continuum, gamma ray line emission, neutron emission or are detected in space by spacecraft. In several flares the second phase is coincident with the start of a type 2 radio burst that is believed to be the signature of a shock wave. Observations from the Solar Maximum Mission spacecraft have shown, for the first time, that several flares accelerate particles to all energies nearly simultaneously. These results posed a new theoretical problem: How fast are shocks and magnetohydrodynamic turbulence formed and how quickly can they accelerate ions to 50 MeV in the lower corona? This problem is discussed.

Decker, R. B.↗
NASA NTRS2000

Reconnection Remnants in the Magnetic Cloud of October 18-19, 1995: A Shock, Monochromatic Wave, Heat Flux Dropout and Energetic Ion Beam

Evidence is presented that the WIND spacecraft observed particle and field signatures on October 18-19, 1995 due to reconnection near the footpoints of a magnetic cloud (i.e., between 1 and 5 solar radii). These signatures include: (1) an internal shock traveling approximately along the axis of the magnetic cloud, (2) a simple compression of the magnetic field consistent with the footpoint magnetic fields being thrust outwards at speeds much greater than the solar wind speed, (3) an electron heat flux dropout occurring within minutes of the shock indicating a topological change resulting from disconnection from the solar surface, (4) a very cold 5 keV proton beam and (5) an associated monochromatic wave. We expect that, given observations of enough magnetic clouds, Wind and other spacecraft will see signatures similar to the ones reported here indicating reconnection. However, these observations require the spacecraft to be fortuitously positioned to observe the passing shock and other signatures and will therefore be associated with only a small fraction of magnetic clouds. Consistent with this, a few magnetic clouds observed by Wind have been found to possess internal shock waves.

Collier, Michael R.↗
NASA NTRS1994

A future, intense source of negative hydrogen ions

By directly heating lithium hydride in a vacuum, up to 18 micro-A/sq cm of negative hydrogen has been obtained from the crystal lattice. The amount of ion current extracted and analyzed is closely related to the temperature of the sample and to the rate at which the temperature is changed. The ion current appears to be emission limited and saturates with extraction voltage. For a fixed extraction voltage, the ion current could be maximized by placing a grid between the sample surface and the extraction electrode. Electrons accompanying the negative ions were removed by a magnetic trap. A Wein velocity filter was designed and built to provide definitive mass analysis of the extracted ion species. This technique when applied to other alkali hydrides may produce even higher intensity beams possessing low values of emittance.

Siefken, Hugh↗