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At least 685 records · Page 38

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NASA NTRS1972

The light ion trough.

A distinct feature of the ion composition results from the OGO-2, 4 and 6 satellites is the light ion trough, wherein the mid-latitude concentrations of H+ and He+ decrease sharply with latitude. In contrast to the 'main trough' in electron density observed primarily as a nightside phenomenon, the light ion trough persists during both day and night. For daytime winter hemisphere conditions and for all seasons during night, the mid-latitude light ion concentration decrease is a pronounced feature. In the dayside summer and equinox hemispheres, the rate of light ion decrease with latitude is comparatively gradual, and the trough boundary is less well defined, particularly for quiet magnetic conditions. In response to magnetic storms, the light ion trough minimum moves equatorward, and deepens, consistent with earlier evidence of the contraction of the plasmasphere in response to storm time enhancements in magnetospheric plasma convection.

Taylor, H. A., Jr.↗

NASA NTRS1972

The light-ion trough, the main trough, and the plasmapause.

Although the plasmapause has been detected as a global phenomenon by both VLF and ion composition measurements, the electron and ion density troughs have been identified primarily as nightside features. This problem, as well as the difficulty in explaining various inconsistencies in relating the position of the plasmapause and the ionization trough, is explained by a close examination of the ion composition, generally unavailable in previous trough studies. In particular, ion composition results from the polar-orbiting Ogo satellites identify the persistence of a pronounced light-ion trough (LIT) in H(+) and He(+), often identified by order-of-magnitude decreases in the light-ion concentrations, that occurs within a few degrees of latitude and reaches residual concentration levels of 100 to 1000 ions/cu cm near 60 deg dipole latitude. The LIT, observed both within the thermosphere and at high latitudes in the magnetosphere, has been correlated directly with the VLF whistler identification of the plasmapause.

Taylor, H. A., Jr.↗

NASA NTRS1973

Metallic ions in the equatorial ionosphere.

Four positive ion composition measurements of the equatorial E region at Thumba, India, are presented. During the day, the major ions between 90 and 125 km are NO+ and O2+. The relative concentrations are similar to those observed at midlatitudes but exhibit unusual structural behavior with altitude. A metallic ion layer centered at 92 km is found to contain Mg+, Fe+, Ca+, K+, Al+, Na+, and possibly Si+ ions. The layer is explained in terms of a similarly shaped altitude distribution of neutral atoms that are photoionized and charge exchanged with NO+ and O2+. Three-body reactions form molecular metallic ions that are rapidly lost by dissociative ion-electron recombination.

Aikin, A. C.↗

NASA NTRS1973

The angular distribution of ion flux around an ionospheric satellite.

Ion measurements from the Explorer 31 satellite were used to determine the angular distribution of ions around the satellite. The ion distributions were compared with the electron distributions measured on the same satellite. It is shown that the electron currents (fluxes) in the wake are always larger than the ion currents for a wide domain of plasma parameters. A quantitative comparison of the ion fluxes with a neutral approximation model for the angular distribution is considered. It is found that the ion fluxes become progressively larger than the corresponding computed neutral fluxes as the angle of attack increases from 0 to 180 deg.

Samir, U.↗

NASA NTRS1974

Ion composition and drift observations in the nighttime equatorial ionosphere

The first in situ measurements of ion composition in the nighttime equatorial E and F region ionospheres (90-300 km) are presented and discussed. These profiles were obtained by two rocket-borne ion mass spectrometers launched from Thumba, India on March 9-10, 1970 at solar zenith angles of 112 deg and 165 deg. Ionosonde data established that the composition was measured at times bounding a period of F region downward drift. During this period the ions O(+) and N(+) were enhanced by one to three orders of magnitude between 220 and 300 km. Below the drift region (200 km), O(+) ceased to be the major ionic constituent, but the concentrations of O(+) and N(+) remained larger than predicted from known radiation sources and loss processes. Here also, both the O2(+) and NO(+) profiles retained nearly the same shape and magnitude throughout the night in agreement with theories assuming scattered UV radiation to be the maintaining source. Light metallic ions including Mg(+), Na(+) and possibly Si(+) were observed to altitude approaching 300 km, while the heavier ions Ca(+) and K(+) were seen in reduced quantity to 200 km. All metal ion profiles exhibited changes which can be ascribed to vertical drifting.

Goldberg, R. A.↗

NASA NTRS1974

Parametric study of ion heating in a burnout device (HIP-1)

Results of further studies on the Lewis Research Center hot-ion plasma source (HIP-1) are reported. Changes have been made in both the electrode geometry and materials to produce higher ion temperatures. Ion temperature increased significantly with increased vacuum pumping speed. The best ion temperatures achieved, so far, for H(+), D(+), and He(+) plasmas are estimated to be equal to, or greater than 0.6, equal to, or greater than 0.9, and equal to, greater than 2.0 keV, respectively. Electrode pairs produced high ion temperatures whether on the magnetic axis or off it by 5.5 cm. Multiple sources, one on-axis and one off-axis, were run simultaneously from a single power supply by using independent gas feed rates. A momentum analyzer has been added to the charge-exchange neutral particle analyzer to identify particles according to mass, as well as energy. Under any given plasma condition, the higher mass ions have higher average energies but not by as much as the ratio of their respective masses.

Sigman, D. R.↗

NASA NTRS1974

Effect of satellite potential on direct ion density measurements through the plasmapause

A simplified theory has been developed for calculating the effect of satellite potential on the ion current measured by an experiment such as an ion mass spectrometer or an ion trap. The theory is based on the use of a spherically symmetric Debye potential distribution in the sheath around the satellite and is particularly appropriate for use in regions where the Debye length is large, such as in the plasmasphere and magnetosphere. Ion data obtained from the ion trap on the Ogo 3 satellite during a pass through the plasmasphere show excellent agreement with the theory. The inferred ion densities from this analysis are as much as 1 order of magnitude different from what would be inferred from previous analyses.

Whipple, E. C.↗

NASA NTRS1974

Some effects of diffusion on the flow of ions in the solar wind

The contribution of diffusive effects to the near equality of flow velocities of H+ and heavier ions of the solar wind at 1 AU is examined. Frictional drag on heavy ions from average solar wind fluxes of H+ appears to make an appreciable contribution to equalizing velocities. The frictional drag on H+ due to the presence of heavy ions may make an appreciable contribution to equalizing flow velocities, since compensating increases in coronal temperatures may be required in order to give solar wind velocities for H+. However, rather large enhancements of heavy ions near the sun appear to be required. If appreciable enhancements of heavy ions extend beyond about 2.5 solar radii, significant increases in heavy ion temperatures above H+ temperatures may be produced. This temperature difference may contribute to equalizing flow velocities and may contribute to the explanation of measured temperature differences at 1 AU between H+ and He++.

Nakada, M. P.↗

NASA NTRS1974

Measurements of positive ion conversion and removal reactions relating to the Jovian ionosphere

Measured rates are presented for the reaction of He(+) ions with H2 (and D2) molecules to form H(+), H2(+), and HeH(+) ions, as well as for the subsequent reactions of H(+) and HeH(+) ions with H2 to form H3(+). The neutralization of H3(+) /and H5(+)/ ions by dissociative recombination with electrons is shown to be fast. The reaction He(+) + H2 is slow (k 1.1 x 10 to the minus 13th cu cm/sec at 300 K) and produces principally H(+) by the dissociative charge transfer branch. It is concluded that there may be a serious bottleneck in the conversion of two of the primary ions of the upper Jovian ionosphere, H(+) and He(+) (which recombine slowly), to the rapidly recombining H3(+) ion.

Johnsen, R.↗

NASA NTRS1976

Double ion production in mercury thrusters

The development of a model which predicts doubly charged ion density is discussed. The accuracy of the model is shown to be good for two different thruster sizes and a total of 11 different cases. The model indicates that in most cases more than 80% of the doubly charged ions are produced from singly charged ions. This result can be used to develop a much simpler model which, along with correlations of the average plasma properties, can be used to determine the doubly charged ion density in ion thrusters with acceptable accuracy. Two different techniques which can be used to reduce the doubly charged ion density while maintaining good thruster operation, are identified as a result of an examination of the simple model. First, the electron density can be reduced and the thruster size then increased to maintain the same propellant utilization. Second, at a fixed thruster size, the plasma density, temperature and energy can be reduced and then to maintain a constant propellant utilization the open area of the grids to neutral propellant loss can be reduced through the use of a small hole accelerator grid.

Peters, R. R.↗

NASA NTRS1975

Hot ion plasma production in HIP-1 using water-cooled hollow cathodes

The paper reports on hot-ion plasma experiments conducted in a magnetic mirror facility. A steady-state E x B plasma was formed by applying a strong radially inward dc electric field near the mirror throats. Most of the results were for hydrogen, but deuterium and helium plasmas were also studied. Three water-cooled hollow cathodes were operated in the hot-ion plasma mode with the following results: (1) thermally emitting cathodes were not required to achieve the hot-ion mode; (2) steady-state operation (several minutes) was attained; (3) input powers greater than 40 kW were achieved; (4) cathode outside diameters were increased from 1.2 cm (uncooled) to 4.4 cm (water-cooled); (5) steady-state hydrogen plasmas with ion temperatures from 185 to 770 eV and electron temperatures from 5 to 21 eV were produced. Scaling relations were empirically obtained for discharge current, ion temperature, electron temperature, and relative ion density as a function of hydrogen gas feed rate, magnetic field, and cathode voltage.

Reinmann, J. J.↗

NASA NTRS1976

Nonpropulsive applications of ion beams

Eight centimeter ion beam sources utilizing xenon and argon have been developed that operate over a wide range of beam energies and currents. Three types of processes have been studied: sputter deposition, ion beam machining, and ion beam surface texturing. The broad range of source operating conditions allows optimum sputter deposition of various materials. An ion beam source was used to ion mill laser reflection holograms using photoresist patterns on silicon. Ion beam texturing was tried with many materials and has a multitude of potential applications.

Hudson, W. R.↗

NASA NTRS1977

Analysis of the theory of high energy ion transport

Procedures for the approximation of the transport of high-energy ions are discussed on the basis of available data on ion nuclear reactions. A straightahead approximation appears appropriate for space applications. The assumption that the secondary-ion-fragment velocity is equal to that of the fragmenting nucleus is inferior to straightahead theory but is of sufficient accuracy if the primary ions display a broad energy spectrum. An iterative scheme for the solution of the inhomogenous integral transport equations holds promise for practical calculation. A model calculation shows that multiple charged ion fragments penetrate to greater depths in comparison with the free path of a primary heavy ion.

Wilson, J. W.↗

NASA NTRS1976

Nonpropulsive applications of ion beams

This paper describes the results of an investigation of the nonpropulsive applications of electric propulsion technology. Eight centimeter ion beam sources utilizing xenon and argon have been developed that operate over a wide range of beam energies and currents. Three types of processes have been studied - sputter deposition, ion beam machining, and ion beam surface texturing. The broad range of source operating conditions allows optimum sputter deposition of various materials. An ion beam source has also been used to ion mill laser reflection holograms using photoresist patterns on silicon. Ion beam texturing has been tried with many materials and has a multitude of potential applications.

Hudson, W. R.↗

NASA NTRS1976

The ion optics of a two grid electron-bombardment thruster

A detailed experimental investigation has been performed to determine the ion beam divergence of an electron-bombardment ion thruster as a function of grid geometry changes. The results show that, to a good approximation, each geometrical grid parameter independently affects one aspect of grid set performance. These observations are used to develop a graphical technique for predicting the ion beam divergence of an arbitrary ion source and grid geometry combination. The usefulness of this technique is demonstrated by comparing predicted ion beam divergence of the 30-cm diameter Engineering Model ion thruster with independent experimental determinations. Good agreement is shown between predicted and experimental results.

Aston, G.↗

NASA NTRS1977

On the formation and destruction of chlorine negative ions in the D region

We have investigated the possible reactions of chlorine atoms, chlorine monoxide, and hydrogen chloride with D region negative ions. The mesospheric concentrations of the neutral chlorine gases have been predicted with a diurnally varying one-dimensional model of the upper atmosphere. Despite the low abundances of chlorine compounds in air their high reactivity leads to the formation of substantial quantities of clorine negative ions at high altitudes. The concentration of chlorine ions is limited in daylight by rapid reactions with oxygen and hydrogen atoms and at night by the competitive production of other stable ions. The presence of chlorine negative ions in the upper atmosphere is consistent with in situ mass spectrometer observations of charged species. The abundance of chlorinated ions in the D region may be correlated with mesospheric nitric oxide and water vapor concentrations.

Turco, R. P.↗

NASA NTRS1977

Ion beam plume and efflux characterization flight experiment study

A flight experiment and flight experiment package for a shuttle-borne flight test of an 8-cm mercury ion thruster was designed to obtain charged particle and neutral particle material transport data that cannot be obtained in conventional ground based laboratory testing facilities. By the use of both ground and space testing of ion thrusters, the flight worthiness of these ion thrusters, for other spacecraft applications, may be demonstrated. The flight experiment definition for the ion thruster initially defined a broadly ranging series of flight experiments and flight test sensors. From this larger test series and sensor list, an initial flight test configuration was selected with measurements in charged particle material transport, condensible neutral material transport, thruster internal erosion, ion beam neutralization, and ion thrust beam/space plasma electrical equilibration. These measurement areas may all be examined for a seven day shuttle sortie mission and for available test time in the 50 - 100 hour period.

Sellen, J. M., Jr.↗

NASA NTRS1978

Ion beam sputter etching and deposition of fluoropolymers

Fluoropolymer etching and deposition techniques including thermal evaporation, RF sputtering, plasma polymerization, and ion beam sputtering are reviewed. Etching and deposition mechanism and material characteristics are discussed. Ion beam sputter etch rates for polytetrafluoroethylene (PTFE) were determined as a function of ion energy, current density and ion beam power density. Peel strengths were measured for epoxy bonds to various ion beam sputtered fluoropolymers. Coefficients of static and dynamic friction were measured for fluoropolymers deposited from ion bombarded PTFE.

Banks, B. A.↗