Engineering topics

Hamilton, D. C.

Publications and source records attributed to Hamilton, D. C..

At least 19 records

NASA NTRS2005

Overview of Results from the Cassini Magnetospheric Imaging Instrument (MIMI) During the First Year of Operations

The MIMI investigation comprises three sensors covering the indicated energy ranges: the Ion and Neutral Camera (INCA) -- 7 keV/nuc 3 Mev) and protons (1.6 < E < 160 Mev) from the back end of the dual field-of-view telescope. The Saturn observation sequences began in January, 2004 and culminated in Saturn Orbit Insertion on July 1, 2004. The MIMI sensors observed substantial activity in interplanetary space for several months prior to SOI, including several interplanetary shocks associated with corotating interaction regions, numerous increases most likely originating from particle streams in the vicinity of the Saturnian bow shock and energetic neutral atoms (ENA) emanating from Saturn s magnetosphere. Results following SOI revealed: a dynamical magnetosphere with a day-night asymmetry and an 11-hour periodicity; several water-product ions (O+, OH+, H2O+), but little N+; inferred quantities of neutral gas sufficient to cause major losses in the trapped ions and electrons in the middle and inner magnetosphere; a Titan exosphere that is a copious source of ENA; INCA imaging through ENA has also revealed a previously unknown radiation belt residing inward of the D-ring that is most likely the result of double charge-exchange between the main radiation belt and the upper layers of Saturn s exosphere. Finally, there is ample evidence for the presence of substorm-like injections of plasma that subsequently corotates for a number of days before dissipating on the night-side magnetotail. The observations will be presented and discussed in the context of current theoretical models.

Krimigis, S. M.↗

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 NTRS2000

Scattering/Transmission of Energetic H+,He+, and O+ Through a Thin Composite Si/Lexan/C Foil

The need for a thin foil to serve both as an extreme ultraviolet (EUV) radiation attenuator and as a secondary electron generator for time-of-flight (TOF) instruments and energetic neutral atom (ENA) imagers has led us to test the scattering and transmission characteristics of a layered foil of nominal aerial thicknesses of 5 micrograms (raised dot) per square centimeter Si, 4 micrograms (raised dot) per square centimeter Lexan (C16H14O3), and 1 microgram (raised dot) per square centimeter C. We report the scattering/transmission results of subjecting this foil to H(+), He(+), and O(+) beams of energies less than or equal to 120 keV. The scattering of these particles, defined by the half-angular-width at half-maximum (HWHM), decreases with increasing energy and found to be 10 degrees for 10 keV H(+), 22 keV for He(+), and 100 keV for O(+). The 50% transmission threshold for these particles was found to be 3.9 keV for H(+), 8.6 keV for He(+), and 49.5 keV for O(+). Computer simulations of H(+)-foil interactions using SRIM96 agree well with the H(+) data, while yielding less scattering and higher transmission than indicated by the O(+) data.

Adrian, M. L.↗

NASA NTRS2000

Scattering/Transmission of Energetic H(sup +), He(sup +), and O(sup +) Through a Thin Composite Si/Lexan/C Foil

The need for a thin foil to serve both as an extreme ultraviolet (EUV) radiation attenuator and as a secondary electron generator for time-of-flight (TOF) instruments and energetic neutral atom (ENA) imagers has led us to test the scattering and transmission characteristics of a layered foil of nominal aerial thicknesses of 5 microns/sq cm Si, 4 microns/sq.cm Lexan ((C16)H(14)O3), and 1 micron/sq.cm C. We report the scattering and transmission results of subjecting this foil to H(sup +), He(sup +), and O(sup +) beams of energy less than 120 keV. The scattering of these particles, defined by the half-angular-width at half-maximum (HWHM), decreases with increasing energy and is found to be 10 deg for 10 keV H(sup +), 22 keV for He(sup +), and 100 keV for O(sup +). The 50% transmission threshold for these particles was found to be 3.9 keV for H(sup +), 8.6 keV for He(sup +), and 49.5 keV for O(sup +). Additionally, ion transmission shows evidence of resonance scattering from a rectangular potential independent of incident ion mass. Particularly evident is a local transmission minimum at 70 keV possessing a Gaussian-width of 20 keV. For incident energies below 50 keV, computer simulations of H+-foil interactions using SRIM96 agree well with the H(sup +) data, while yielding less scattering and higher transmission than indicated by the O(sup +) data.

Adrian, M. L.↗

NASA NTRS1997

Solar Cycle Dynamics of Solar, Magnetospheric, and Heliospheric Particles, and Long-Term Atmospheric Coupling: SAMPEX

This report summarizes science analysis activities by the SAMPEX mission science team during the period during the period July 1, 1997 through July 1, 1997. Bibliographic entries for 1996 and 1997 to date (July 1997) are included. The SAMPEX science team was extremely active, with 27 articles published or submitted to refereed journals, 17 papers published in their entirety in Conference Proceedings, and 74 contributed papers, seminars, and miscellaneous presentations. The bibliography at the end of this report constitutes the primary description of the research activity. Science highlights are given under the major activity headings, as well as other activities of the team.

Mason, G. M.↗

NASA NTRS1996

Solar cycle dynamics of solar, magnetospheric, and heliospheric particles, and long-term atmospheric coupling: SAMPLEX

This report summarizes science analysis activities by the SAMPEX mission science team during the period during the period July 1, 1995 through July 1, 1996. Bibliographic entries for 1995 and 1996 to date (July 1996) are included. The SAMPEX science team was extremely active, with 20 articles published or submitted to refereed journals, 18 papers published in their entirety in Conference Proceedings, and 53 contributed papers, seminars, and miscellaneous presentations. The bibliography at the end of this report constitutes the primary description of the research activity. Science highlights are given under the major activity headings of anomalous cosmic rays, solar energetic particles, magnetospheric precipitating electrons, trapped H and He isotopes, and data analysis activities.

Mason, G. M.↗

NASA NTRS1995

Elemental and charge state composition of the fast solar wind observed with SMS instruments on WIND

The elemental composition and charge state distributions of heavy ions of the solar wind provide essential information about: (1) atom-ion separation processes in the solar atmosphere leading to the 'FIP effect' (the overabundance of low First Ionization potential (FIP) elements in the solar wind compared to the photosphere); and (2) coronal temperature profiles, as well as mechanisms which heat the corona and accelerate the solar wind. This information is required for solar wind acceleration models. The SWICS instrument on Ulysses measures for all solar wind flow conditions the relative abundance of about 8 elements and 20 charge states of the solar wind. Furthermore, the Ulysses high-latitude orbit provides an unprecedented look at the solar wind from the polar coronal holes near solar minimum conditions. The MASS instrument on the WIND spacecraft is a high-mass resolution solar wind ion mass spectrometer that will provide routinely not only the abundances and charge state of all elements easily measured with SWICS, but also of N, Mg, S. The MASS sensor was fully operational at the end of 1994 and has sampled the in-ecliptic solar wind composition in both the slow and the corotating fast streams. This unique combination of SWICS on Ulysses and MASS on WIND allows us to view for the first time the solar wind from two regions of the large coronal hole. Observations with SWICS in the coronal hole wind: (1) indicate that the FIP effect is small; and (2) allow us determine the altitude of the maximum in the electron temperature profile, and indicate a maximum temperature of approximately 1.5 MK. New results from the SMS instruments on Wind will be compared with results from SWICS on Ulysses.

Gloeckler, G.↗

NASA NTRS1995

Iron charge states in the solar wind as measured by SMS on Wind

The Wind spacecraft was launched in November 1994. In the first half of 1995 it was in the interplanetary medium upstream of the Earth. The Solar Wind and Suprathermal Ion Composition Experiment (SMS) on Wind consists of three sensors, the Solar Wind Ion Composition Spectrometer (SWICS), the Suprathermal Ion Composition Spectrometer (STICS), and the high mass resolution spectrometer (MASS). All three instruments utilize electrostatic deflection combined with time-of-flight measurement. The data from these three sensors allows the determination of the ionic composition of the solar wind in a variety of solar wind conditions over a large energy/charge range (0.5 to 230 keV/e). We have examined the Wind database for time periods conducive to observing solar wind iron. With the high mass resolution of the MASS spectrometer (M/Delta-M greater than 100) iron is easily identified while the electrostatic deflection provides information concerning the mass/charge distribution. We present here the relative abundance of iron charge states in the solar wind near 1 AU.

Galvin, A. B.↗

NASA NTRS1995

SWICS/Ulysses and MASS/wind observations of solar wind sulfur charge states

As Ulysses journeys from the southern to the northern solar pole, the newly launched Wind spacecraft is monitoring the solar wind near 1 AU, slightly upstream of the Earth. Different solar wind structures pass over both spacecraft as coronal holes and other features rotate in and out of view. Ulysses and Wind are presently on opposing sides of the sun allowing us to monitor these streams for extended periods of time. Composition measurements made by instruments on both spacecraft provide information concerning the evolution and properties of these structures. We have combined data from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses and the high mass resolution spectrometer (MASS) on Wind to determine the charge state distribution of sulfur in the solar wind. Both instruments employ electrostatic deflection with time-of-flight measurement. The high mass resolution of the MASS instrument (M/Delta-M approximately 100) allows sulfur to be isolated easily while the stepping energy/charge selection provides charge state information. SWICS measurements allow the unique identification of heavy ions by their mass and mass/charge with resolutions of M/Delta-M approximately 3 and M/q/Delta(M/q) approximately 20. The two instruments complement each other nicely in that MASS has the greater mass resolution while SWICS has the better mass/charge resolution and better statistics.

Cohen, C. M. S.↗

NASA NTRS1995

Charge state of anomalous cosmic-ray nitrogen, oxygen, and neon: SAMPEX observations

We report observations of the ionization state of anomalous cosmic-ray (ACR) nitrogen, oxygen, and neon during the period 1992 October to 1993 May, carried out with instrumentation on the Solar, Anomalous & Magnetospheric Particle Explorer (SAMPEX) spacecraft. The low-altitude (510 x 675 km) and high-inclination (82 deg) orbit enables SAMPEX to sample the interplanetary ACR fluxes on each polar pass and then to observe the cutoff of these fluxes by the geomagnetic field at lower latitudes. The arrival time and direction of each ion is recorded by the instruments, allowing detailed calculations of the particle's trajectory through the Earth's magnetic field and thereby placing upper limits on the ionization state of the particles. We find (a) that ACR nitrogen, oxygen, and neon each contain singly ionized particles and (b) that ACR oxygen is predominantly singly ionized with an upper limit of 10% for higher ionization states. These ionization states confirm theories of ACR origin as neutral interstellar material that is singly ionized near the Sun by UV or charge exchange with the solar wind, and is subsequently accelerated in the outer heliosphere.

Klecker, B.↗

NASA NTRS1995

The relationship between kappa and temperature in energetic ion spectra at Jupiter

A universal energy per charge kappa function fit is simultaneously applied to the spectra of Voyager 2 Low Energy Charged Particle (LECP) proton, helium, oxygen, sulfur, and carbon ions during 33 Jovian plasma sheet crossings from 26 to 160 R(sub J). The fits yield an approximately linear relationship between high energy spectral index, kappa, and core proton temperature of the form kappa (T(sub H)) approximately = eta dot T(sub H) + kappa(sub 0) with eta = 0.080 ke/V, kappa(sub 0) = 2.86, and T(sub H) measured in keV. Core proton temperatures range from 5 to 35 keV with spectral indices ranging from 3 to 6.

Collier, Michael R.↗

NASA NTRS1994

High charge state carbon and oxygen ions in Earth's equatorial quasi-trapping region

Observations of energetic (1.5 - 300 keV/e) medium-to-high charge state (+3 less than or equal to Q less than or equal to +7) solar wind origin C and O ions made in the quasi-trapping region (QTR) of Earth's magnetosphere are compared to ion trajectories calculated in model equatorial magnetospheric magnetic and electric fields. These comparisons indicate that solar wind ions entering the QTR on the nightside as an energetic component of the plasma sheet exit the region on the dayside, experiencing little or no charge exchange on the way. Measurements made by the CHarge Energy Mass (CHEM) ion spectrometer on board the Active Magnetospheric Particle Tracer Explorer/Charge Composition Explorer (AMPTE/CCE) spacecraft at 7 less than L less than 9 from September 1984 to January 1989 are the source of the new results contained herein: quantitative long-term determination of number densities, average energies, energy spectra, local time distributions, and their variation with geomagnetic disturbance level as indexed by Kp. Solar wind primaries (ions with charge states unchanged) and their secondaries (ions with generally lower charge states produced from primaries in the magnetosphere via charge exchange)are observed throughout the QTR and have distinctly different local time variations that persist over the entire 4-year analysis interval. During Kp larger than or equal to 3 deg intervals, primary ion (e.g., O(+6)) densities exhibit a pronounced predawn maximum with average energy minimum and a broad near-local-noon density minimum with average energy maximum. Secondary ion (e.g., O(+5)) densities do not have an identifiable predawn peak, rather they have a broad dayside maximum peaked in local morning and a nightside minimum. During Kp less than or equal to 2(-) intervals, primary ion density peaks are less intense, broader in local time extent, and centered near midnight, while secondary ion density local time variations diminish. The long-time-interval baseline helps to refine and extend previous observations; for example, we show that ionospheric contribution to O(+3)) is negligible. Through comparison with model ion trajectories, we interpret the lack of pronounced secondary ion density peaks colocated with the primary density peaks to indicate that: (1) negligible charge exchange occurs at L greater than 7, that is, solar wind secondaries are produced at L less than 7, and (2) solar wind secondaries do not form a significant portion of the plasma sheet population injected into the QTR. We conclude that little of the energetic solar wind secondary ion population is recirculated through the magnetosphere.

Christon, S. P.↗

NASA NTRS1993

The return of the anomalous cosmic rays to 1 Au in 1992

New observations of low energy (approximately 1 to 200 MeV/nuc) cosmic rays measured by three newly launched experiments on Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) during 1992 and 1993 show the strong presence of anomalous cosmic ray (ACR) nitrogen and oxygen, well before the approaching solar minimum. When compared with ACR temporal variations over the past two solar cycles we find that the 1992-1993 fluxes are approximately 5 to 10 times their level at corresponding neutron monitor counting rates in 1969-1970 and 1985.

Mewaldt, R. A.↗

NASA NTRS1993

Ion transport and loss in the earth's quiet ring current. I - Data and standard model

A study of the transport and loss of ions in the earth's quiet time ring current, in which the standard radial diffusion model developed for the high-energy radiation belt particles is compared with the measurements of the lower-energy ring current ions, is presented. The data set provides ionic composition information in an energy range that includes the bulk of the ring current energy density, 1-300 keV/e. Protons are found to dominate the quiet time energy density at all altitudes, peaking near L of about 4 at 60 keV/cu cm, with much smaller contributions from O(+) (1-10 percent), He(+) (1-5 percent), and He(2+) (less than 1 percent). A minimization procedure is used to fit the amplitudes of the standard electric radial diffusion coefficient, yielding 5.8 x 10 exp -11 R(E-squared)/s. Fluctuation ionospheric electric fields are suggested as the source of the additional diffusion detected.

Sheldon, R. B.↗

NASA NTRS1993

Electromagnetic ion cyclotron waves stimulated by modest magnetospheric compressions

AMPTE/CCE magnetic field and particle data are used to test the suggestion that increased hot proton temperature anisotropy resulting from convection during magnetospheric compression is responsible for the enhancement in Pc 1 emission via generation of electromagnetic ion cyclotron (EMIC) waves in the dayside outer equatorial magnetosphere. The relative increase in magnetic field is used to gauge the strength of the compression, and an image dipole model is used to estimate the motion of the plasma during compression. Proton data are used to analyze the evolution of the proton distribution and the corresponding changes in EMIC wave activity expected during the compression. It is suggested that enhancements in dynamic pressure pump the energetic proton distributions in the outer magnetosphere, driving EMIC waves. Waves are expected to be generated most readily close to the magnetopause, and transient pressure pulses may be associated with bursts of EMIC waves, which would be observed on the ground in association with ionospheric transient signatures.

Anderson, B. J.↗

NASA NTRS1993

The role of ring current nose events in producing stable auroral red arc intensifications during the main phase - Observations during the September 19-24, 1984, equinox transition study

A set of observations describing ionospheric conditions, magnetospheric populations, and 6300-A emission intensities on stable auroral red (SAR) arc field lines during the solar minimum 19-24 Sept. 1984 magnetic storm period prompted a study of solar cycle and magnetic storm phase variations in SAR arc emissions and their magnetospheric energy source. It was found that medium-energy H(+) was significantly enhanced during the main phase compared to the late recovery phase of the 19-20 Sept. 1984 storm. Enhanced heating of the thermal electron plasma caused by this population resulted in more than an order of magnitude greater SAR arc emissions in the main phase compared to the recovery phase. O(+) was found to be the dominant energy source for SAR arcs in the late recovery phases of storms in the 19-24 Sept. period.

Kozyra, J. U.↗

NASA NTRS1993

Origin, transport, and losses of energetic He(+) and He(2+) ions in the magnetosphere of the Earth - AMPTE/CCE observations

Data from the ion charge-energy-mass spectrometer CHEM flown on AMPTE/CCE spacecraft are used to investigate the origin, transport, and losses of energetic He(+) and He(2+) ions in the earth's magnetosphere. The L profiles of the average ion phase space density f were determined as a function of the magnetic momentum. It is shown that the L profiles have an inner part, where f increases with L for both He(+) adn He(2+) and where steady-state conditions are fulfilled. The outer boundary L(lim) of this region is located at a distance that depends on the ion species and the geomagnetic activity level. Steady-state conditions continue outside L(lim) for He(+) ions, while the He(2+) ion distribution outside L(lim) is strongly influenced by ion convection causing a lack of steady-state conditions. It is concluded that solar wind is the origin of the He(2+), while a mixed origin is suggested for the He(+) ions, in which the major contribution is from the solar wind via charge exchange production from the He(2+) ions.

Kremser, G.↗

NASA NTRS1992

Radial profiles of quiet time magnetospheric parameters

The quiet time magnetosphere is studied using ion measurements covering energies from about 1 keV to about 4 MeV from selected passes of the Charge Composition Explorer during low geomagnetic activity. The quiet time plasma pressure in the midnight sector was found to be comparable to that deduced by Spence et al. (1989) and Kan et al. (1992) from inverting the magnetic field models of Tsyganenko and Usmanov (1982) and Tsyganenko (1987). The radial profile of the total plasma pressure exhibited a peak at L = 3-4 and decreased monotonically from L = 4 and L = 9. Contrary to theoretical expectations for the magnetospheric closure of the region 2 field-aligned current system, no large-scale earthward decrease in plasma pressure was found to occur in these outer L shells.

Lui, A. T. Y.↗