Engineering topics

Ghielmetti, A. G.

Publications and source records attributed to Ghielmetti, A. G..

8 records

NASA NTRS2012

Heliospheric Neutral Atom Spectra Between 0.01 and 6 keV fom IBEX

Since 2008 December, the Interstellar Boundary Explorer (IBEX) has been making detailed observations of neutrals from the boundaries of the heliosphere using two neutral atom cameras with overlapping energy ranges. The unexpected, yet defining feature discovered by IBEX is a Ribbon that extends over the energy range from about 0.2 to 6 keV. This Ribbon is superposed on a more uniform, globally distributed heliospheric neutral population. With some important exceptions, the focus of early IBEX studies has been on neutral atoms with energies greater than approx. 0.5 keV. With nearly three years of science observations, enough low-energy neutral atom measurements have been accumulated to extend IBEX observations to energies less than approx. 0.5 keV. Using the energy overlap of the sensors to identify and remove backgrounds, energy spectra over the entire IBEX energy range are produced. However, contributions by interstellar neutrals to the energy spectrum below 0.2 keV may not be completely removed. Compared with spectra at higher energies, neutral atom spectra at lower energies do not vary much from location to location in the sky, including in the direction of the IBEX Ribbon. Neutral fluxes are used to show that low energy ions contribute approximately the same thermal pressure as higher energy ions in the heliosheath. However, contributions to the dynamic pressure are very high unless there is, for example, turbulence in the heliosheath with fluctuations of the order of 50-100 km/s.

Fuselier, S. A.↗

NASA NTRS1990

High mass resolution isochronous time-of-flight spectrograph for three-dimensional space plasma measurements

By combining a toroidal electrostatic analyzer with a novel cylindrically symmetric isochronous time-of-flight mass spectrometer, an instrument was developed that simultaneously determines the three-dimensional distribution function of ions and differentiates species. The ion mass is determined to high resolution (M/Delta-M greater than 50) from the time of flight within a harmonic field configuration defined by hyperboloid equipotential surfaces. A second conventional time-of-flight channel makes use of particles leaving the thin entrance foil as neutrals. An additional solid state detector in which the neutrals are stopped allows the total energy and thereby the ionic charge of the incident ions to be determined as well. Information from the neutral and the ion channels can be combined to determine the total mass of an incident molecular ion and the mass of one atomic fragment.

Moebius, E.↗

NASA NTRS1987

Experimental tests of a toroidal electrostatic analyzer

A toroidal electrostatic analyzer of a design suitable for space plasma instrumentation has been constructed and tested. Experimental results are compared with second-order ion optical theory and are in good agreement. Verifying the ion optics of the toroid was simplified by use of a position-sensing microchannel-plate detector mounted on a positioning system with three translational degrees of freedom located at the toroid exit. The toroidal analyzer described here is the first optical element in a fully toroidal mass spectrograph intended for analysis of kilovolt magnetospheric plasmas.

Young, D. T.↗

NASA NTRS1986

Ion composition and dynamics at comet Halley

The Giotto space probe's ion mass spectrometer has obtained data on the composition and velocity distributions of cometary ions at distances of between 7.5 million and 1300 km from the comet Halley nucleus. Solar wind He(2+) was found throughout the coma, as close as 5000 km, with the He(+) produced by charge exchange being within about 200,000 km. A pile-up of heavy cometary ions was found at about 10,000 km from the nucleus. Inside the contact surface, which was found at about 4600 km, ion temperatures as low as about 340 K and outflow velocities of about 1 km/sec were found.

Balsiger, H.↗

NASA NTRS1986

Observations of transverse and parallel acceleration of terrestrial ions at high latitudes

Selected S3-3 satellite ion-mass-spectrometer observations of upward-flowing 0.5-16-keV terrestrial ions in the auroral zones at altitudes 2000-8000 km are presented graphically and analyzed. The data are shown to support an interpretation in which ion conics are first formed at lower altitudes (by a mechanism which provides more energy to heavier ions) and then accelerated upward through a potential drop; outside these regions ion conics may be generated by mechanisms which are independent of ion mass.

Collin, H. L.↗

NASA NTRS1986

Ion specific differences in energetic field aligned upflowing ions at 1 earth radius

An ion-upflow event over the northern auroral zone during a small magnetic storm on August 24, 1976 is characterized on the basis of S3-3 satellite ion-mass-spectrometer observations at 0.5-16 keV. The data are presented in tables, graphs, and diagrams and analyzed in detail. The distributions of upward-flowing O(+) and H(+) associated with parallel electric fields below the satellite are shown to have transverse temperatures of about 1 keV and 0.1 keV, respectively, while the corresponding parallel temperatures were about 1 keV and 0.6 keV; the average energy of the O(+) ions is found to be 2-3 times greater than that of the H(+) ions in the acceleration regions. Possible interpretations of these findings are discussed.

Ghielmetti, A. G.↗

NASA NTRS1983

Hot plasma composition results from the S3-3 spacecraft

The S3-3 satellite discovered the principal auroral acceleration region at altitudes of about 1 R(E) over the auroral zone. Intense fluxes of upward flowing O(+) and H(+) ions with keV energies were commonly observed in this region of the magnetosphere. The detailed morphology of these upflowing ions is described, including their latitude, local time, altitude, and magnetic activity dependences and their relationship to the trapped keV electron population. The first measurements of the composition of the trapped keV ions in the radiation belts are also described, showing the importance of the ionospheric source term to the storm time population of ions with energies equal to or less than 16 keV/e.

Sharp, R. D.↗

NASA NTRS1982

The polar ionosphere as a source of energetic magnetospheric plasma

Data are presented on an additional ionospheric source composed of ions flowing upward out of the high latitude polar cap with energies in the range of approximately 10 eV to more than about 100 eV. The data are from the energetic ion composition spectrometer (EICS) on board the Dynamics Explorer-1 satellite, launched in August 1981. It is noted that the results presented are not inconsistent with the existence of a polar wind of the type predicted by Axford (1968) since ions with energies less than about 1 eV would have been excluded from the instrument by the generally positive vehicle potential. The results suggest that the polar wind is either modified in mass composition and energy by some as yet unidentified process or is supplemented by a new unrelated source of plasma. What is more, owing to the higher energies, the energetic polar cap ions described here enter the plasma sheet at greater distances than Cowley (1980) estimated and probably represent a significant source of plasma for the maintenance of the plasma sheet.

Shelley, E. G.↗