Engineering topics

Ackerson, K. L.

Publications and source records attributed to Ackerson, K. L..

At least 37 records · Page 2

NASA NTRS1980

A Recoverable Plasma Diagnostics Package (RPDP) for Spacelab

The RPDP is a fully instrumented, ejectable and recoverable unit with flight and ground support systems so that it can be utilized attached to the orbiter remote manipulator system, tethered from the orbiter, or as an orbiter subsatellite. Core instruments on the RPDP are flight proven hardware which provide diagnostics measurements of energetic particles, AC electromagnetic and electrostatic waves, vector magnetic field signatures of current systems, vector electric field signatures associated with plasma flow and particle acceleration, thermal plasma ion composition and density, thermal plasma electron density and temperature, and images of optical emissions regions in UV or visible wavelengths.

Shawhan, S. D.↗

NASA NTRS1980

Plasmas in Saturn's magnetosphere

The solar wind plasma analyzer on board Pioneer 2 provides first observations of low-energy positive ions in the magnetosphere of Saturn. Measurable intensities of ions within the energy-per-unit charge (E/Q) range 100 eV to 8 keV are present over the planetocentric radial distance range about 4 to 16 R sub S in the dayside magnetosphere. The plasmas are found to be rigidly corotating with the planet out to distances of at least 10 R sub S. At radial distances beyond 10 R sub S, the bulk flows appear to be in the corotation direction but with lesser speeds than those expected from rigid corotation. At radial distances beyond the orbit of Rhea at 8.8 R sub S, the dominant ions are most likely protons and the corresponding typical densities and temperatures are 0.5/cu cm and 1,000,000 K, respectively, with substantial fluctuations. It is concluded that the most likely source of these plasmas in the photodissociation of water frost on the surface of the ring material with subsequent ionization of the products and radially outward diffusion. The presence of this plasma torus is expected to have a large influence on the dynamics of Saturn's magnetosphere since the pressure ratio beta of these plasmas approaches unity at radial distances as close to the planet as 6.5 R sub S. On the basis of these observational evidences it is anticipated that quasi-periodic outward flows of plasma, accompanied with a reconfiguration of the magnetosphere beyond about 6.5 R sub S, will occur in the local night sector in order to relieve the plasma pressure from accretion of plasma from the rings.

Frank, L. A.↗

NASA NTRS1979

Several recent findings concerning the dynamics of the earth's magnetotail

Several recent results concerning the nature of earth's magnetotail are briefly reviewed. These observational findings include: (1) the three-dimensional character of the plasma sheet via a comprehensive survey of proton bulk flows, (2) a region of earthward-flowing plasmas at the interfaces of the plasma sheet and magnetotail lobes during magnetic substorm recovery, and (3) the signature of electrostatic acceleration for protons within the jetting plasmas from magnetotail fireballs.

Frank, L. A.↗

NASA NTRS1978

Three-dimensional plasma measurements within the earth's magnetosphere

Magnetospheric measurements of three-dimensional velocity distributions for positive ions and electrons in the energy range from 1 eV to 45 keV are reported which were obtained with quadrispherical Lepedeas on ISEE 1 and 2. The instrumentation is briefly described, and an extension of energy-time spectrograms to three-dimensional summaries via the use of ancillary energy-spin phase spectrograms for multiple analyzers is outlined. Macroscopic plasma parameters for two crossings of the dayside magnetopause are presented, along with a preliminary evaluation of the kinematical motions of low-energy charged particles within the terrestrial ring current. Nonmonotonic electron velocity distributions presumably related to the generation of electron cyclotron harmonic instabilities are examined. The possible signature of diffusion driven by electrostatic waves is considered, and velocity distributions of positive ions in the dawn magnetotail are investigated.

Frank, L. A.↗

NASA NTRS1978

Plasma flows and magnetic field vectors in the plasma sheet during substorms

A detailed study of the plasma flow and the magnetic field vector in the plasma sheet during magnetospheric substorms is made to determine whether plasma flows are field-aligned or crossfield. It is shown that there is generally a large magnetic field-aligned component in the rapid plasma flow observed in the plasma sheet during substorms. In particular, the larger the observed flow speed, the closer the observed flow direction is aligned with the magnetic field line. There is no clear association between the plasma flow direction and the sign of the Bz component of the magnetic field during plasma sheet thinnings at substorms. The rapid plasma flows observed in the magnetotail are predominantly magnetic field-aligned.

Lui, A. T. Y.↗

NASA NTRS1978

Quadrispherical LEPEDEAS for ISEE's-1 and -2 plasma measurements

A new generation of spaceflight instrumentation for comprehensive measurements of plasmas within the earth's magnetosphere and its environs is described. These quadrispherical low energy proton and electron differential energy analyzers (LEPEDEAS) for the ISEE's-1 and -2 spacecraft are capable of determining the directional intensities of positive ions and electrons over all but 2 percent of the 4 pi sr solid angle for charged-particle velocity vectors at the spacecraft positions. The energy range of this instrumentation is E/Q of 1 eV to 45 keV with good energy and angular resolutions. An example of inflight observations within the earth's magnetosheath is presented.

Frank, L. A.↗

NASA NTRS1978

Plasma flow pulsations in earth's magnetic tail

On November 9, 1972 Imp 7 was in the plasma sheet from 0430 to 1000 UT and detected strong earthward plasma flows. A series of nine temporal pulsations were observed to vary in bulk speed from 0 to about 1500 km/s and to occur at 15-30 minute intervals. A positive correlation exists between the speed variations and changes in the standard deviation of the magnetic field. Evident periodicity was not found corresponding to Imp 7 pulsations and other magnetospheric or solar wind data. It is felt that the pulsations may indicate that tail reconnection is unsteady in periods of 10-30 minutes.

Coroniti, F. V.↗

NASA NTRS1978

Correlated electric field and low-energy electron measurements in the low-altitude polar cusp

Correlated electric field and low-energy electron measurements are presented for two passes of Hawkeye 1 through the south polar cusp at 2000-km altitude during local morning. In one case the electric field reversal coincides with the boundary of detectable 5.2keV electron intensities and the equatorward boundary of the cusp. In the other case the electric field reversal and the 5.2 keV electron trapping boundary coincide, but the equatorward edge of the cusp as determined from the presence of 180 eV electron intensities is 5 degrees invariant latitude equatorward of the electric field reversal. It is concluded that in the second case, electron intensities associated with the polar cusp populate closed dayside field lines, and hence the corresponding equatorward edge of these electron intensities is not always an indicator of the boundary between closed dayside field lines and polar cap field lines.

Kintner, P. M.↗

NASA NTRS1977

Systematic study of plasma flow during plasma sheet thinnings

On the basis of a study of Imp 6 measurements of plasma flow, it is concluded that there is no clear indication of a predominance of tailward plasma flow beyond about X = -15 R sub E in the midnight sector of the plasma sheet during the expansive phase of a substorm. In fact, it is shown statistically that sunward plasma flow is more frequently observed in the midnight sector within about 30 R sub E from the earth than in any other direction during plasma sheet thinning at the substorm expansion. This result supports the conclusion that there is no definite evidence for the formation of a reconnection neutral line in the near-earth plasma sheet during most substorms.

Lui, A. T. Y.↗

NASA NTRS1977

Reply in response to comment by E. W. Hones

Hones 1977 points out the marked disagreement between the plasma flow measurements reported by Frank et al. 1976 and those obtained with the LASL plasma analyzer. He suggests (1) that solar ultraviolet background rates may have been incorrectly accounted for in the computation of proton bulk flows in the magnetotail as reported by Frank et al. 1976 and (2) that bulk flows with substantial speeds, i.e., those speeds greater than 50 km per sec, are seldom encountered in the plasma sheet at geocentric radial distances approx. equal to 35 R sub E. It is demonstrated that such ultraviolet responses were carefully considered by Frank et al. 1976 and thus the conclusion is maintained that bulk flows greater than 50 km per sec frequently occur in the plasma sheet at these radial distances. Further, a direct comparison of the capabilities of the LASL plasma analyzer employed by Hones and of the LEPEDEA Frank et al., 1976 indicates that there are rather severe restrictions on which plasmas in the plasma sheet can be properly measured to gain proton temperatures, number densities and flow velocities with the LASL plasma analyzer.

Frank, L. A.↗

NASA NTRS1977

Observations of atomic oxygen /O/+// in the earth's magnetotail

The electrostatic analyzer aboard Imp 7 examined energy spectra of positive ions in certain streaming plasmas adjacent to the plasma sheet and within the geomagnetic tail at geocentric radial distances of about 35 R-E, revealing minor, though often persistent, secondary maxima of intensities with energy per unit charge a factor of 16 greater than that of the maxima corresponding to the dominant H(+) ions. The secondary maximum at higher E/Q was identified as a small flux of singly ionized atomic oxygen O(+), from the ionosphere. O(+) fluxes in the geomagnetic tail were about 10 to the 5th/(sq cm s) and imply O(+) upward fluxes in the upper ionosphere of about 10 to the 8th/(sq cm s). The kinetic energy of the oxygen ions is about 1-5 keV, while estimates of the global escape of the ions are about 3 x 10 to the 6th kg/yr.

Frank, L. A.↗

NASA NTRS1976

On tenuous plasmas, fireballs, and boundary layers in the earth's magnetotail

The plasma instrumentation (the Lepedea) and the magnetometer aboard IMP 8 performed correlative measurements of magnetic fields and plasmas within the geomagnetic tail at geocentric radial distances of about 23-46 R-E during March-October 1974. The hot tenuous plasmas within the plasma sheet were found to be in a state of almost continuous flow and were threaded with northward, or closed geomagnetic lines. The satellite encountered a region of acceleration in the magnetotail, the 'fireball' which exhibits strong jetting of plasmas in excess of 1000 km/s, proton temperatures of about 10 to the 7th K, disordered magnetic fields, southward magnetic fields during tailward jetting of plasmas, and northward magnetic fields for fast plasma flows toward earth. In addition, the magnetosheath plasmas within the boundary layers which are contiguous to the plasma sheet display evidence of plasma heating, great changes in bulk flow velocities, and acceleration of energetic electrons with an energy of greater than 45 keV.

Frank, L. A.↗

NASA NTRS1976

Observations of plasmas in the Jovian magnetosphere

This paper presents an analysis of observations of large intensities of low-energy protons deep within the Jovian magnetosphere which were made by Pioneer 10 with an electrostatic plasma analyzer having an energy range from 108 eV to 4.80 keV. A proton density profile plotted against the earth-received time of the satellite signals reveals four significant plasma features: (1) a 'plasmasphere' with relatively high proton densities, located inside the flux tubes of Io at 6 Jupiter radii and extending toward the planet to at least 2.8 radii; (2) a 'plasmapause', on which Io's flux tubes are positioned; (3) a sparse sporadic zone beyond Io, extending out to 8 Jupiter radii; and (4) a ring current beginning at 8 radii, which extends outward in the form of a thin plasma disk and in which Europa is embedded. The thermal energies of the protons in each zone are determined, and it is suggested that Jupiter's ionosphere is the source of these protons. It is noted that the relationship of Io to the 'plasmapause' is probably of fundamental importance to that satellite's modulation of Jovian decametric radio emissions.

Frank, L. A.↗

NASA NTRS1976

Electron precipitation in the postmidnight sector of the auroral zones

Measurements of the angular distributions and energy spectra of electron intensities within the energy range 50 eV to 15 keV with electrostatic analyzer arrays on board the low-altitude satellite Injun 5 are reported for the postmidnight sector of the auroral zones during the high-intensity events accompanying magnetic substorms. Precipitation features on closed terrestrial field lines well equatorward of the trapping boundary for electrons with energies greater than 45 keV are examined. Precipitation of low-energy electron intensities was characterized by isotropy for all pitch angles outside the atmospheric backscatter cone. The region of electron precipitation observed is associated with the diffuse aurora and with pulsating aurora in the postmidnight sector. Similar variations of the energetic electron intensities with energies above 45 keV were observed in the regions of fluctuating energy fluxes of low-energy electrons associated with auroral luminosity. The increases of energetic electron intensities were not coincident with those of the principal energy fluxes into the atmosphere, except when the average electron energy for the energy fluxes was unusually high, i.e., in the 10-keV range. Precipitation of electron intensities within these energy ranges is consistent with strong pitch angle diffusion of electron intensities near or at the magnetic equator by high-frequency wave turbulence, the effectiveness of which is modulated by perturbations attributable to micropulsations.

Frank, L. A.↗

NASA NTRS1976

Examples of plasma flows within the earth's magnetosphere

Examples of observed plasma flows in the dayside magnetosphere near the magnetopause, within the ring current in the local evening sector, and at two positions simultaneously in the plasma sheet are presented. These measurements were gained with plasma instruments on the IMP 6 and 7 satellites. Flow velocities inside the magnetopause in the dayside magnetosphere are typically 25 to 75 km/s and are directed generally parallel to the tangent to the nearby magnetopause with a small component directed into this boundary. Bulk flow speeds within the ring current ranged from the instrument threshold of about 20 km/s to speeds of 50 km/s. Strong tailward 'jetting' of plasma, in the range of 200 to 300 km/s, at geocentric radial distances of about 35 earth radii in the plasma sheet is found to be often associated with the occurrence of magnetic substorms.

Frank, L. A.↗

NASA NTRS1975

Electron precipitation in the post midnight sector of the auroral zones

Comprehensive measurements of the angular distributions and energy spectra of electron intensities with electrostatic analyzer arrays on board the low-altitude satellite Injun 5 are reported. These are for the post-midnight sector of the auroral zones during the high-intensity events accompanying magnetic substorms. Precipitation features on closed terrestrial field lines well equatorward of the trapping boundary for energetic electrons with E greater than 45 keV were examined. No evidences of maxima in the differential energy spectra or of strongly field-aligned currents which are indicative of quasi-static electric fields aligned parallel to the geomagnetic field were found. Precipitation of low-energy electron intensities fluctuated on time scales greater than 2 seconds as viewed at the satellite position. This precipitation was characterized by isotropy for all pitch angles outside the atmospheric backscatter cone.

Frank, L. A.↗

NASA NTRS1974

Plasma wave turbulence at distant crossings of the plasma sheet boundaries and the neutral sheet

The orbit of IMP 7 frequently takes the spacecraft across the neutral sheet in the geomagnetic tail at a downstream distance of about 35 earth radii. This preliminary report discusses the detection of strong low-frequency electromagnetic signals and moderate electrostatic noise enhancements near local midnight. Data used were obtained during a substorm period on Oct. 28, 1972, when there were multiple crossings of the neutral sheet and the boundary of the plasma sheet.

Scarf, F. L.↗

NASA NTRS1972

Local-time survey of plasma at low altitudes over the auroral zones.

Local-time survey of the low-energy proton and electron intensities precipitated into the earth's atmosphere over the auroral zones during periods of magnetic quiescence. This survey was constructed by selecting a typical individual satellite crossing of this region in each of eight local-time sectors from a large library of similar observations with the polar-orbiting satellite Injun 5. The trapping boundary for more-energetic electron intensities, E greater than 45 keV, was found to be a 'natural coordinate' for delineating the boundary between the two major types of lower-energy, 50 less than or equal to E less than or equal to 15,000 eV, electron precipitation commonly observed over the auroral zones at low altitudes. Poleward of this trapping boundary inverted 'V' electron precipitation bands are observed in all local-time sectors. These inverted 'V' electron bands in the evening and midnight sectors are typically more energetic and have greater latitudinal widths than their counterparts in the noon and morning sectors. In general, the main contributors to the electron energy influx into the earth's atmosphere over the auroral zones are the electron inverted 'V' precipitation poleward of the trapping boundary in late evening, the plasma-sheet electron intensities equatorward of this boundary in early morning, and both of these precipitation events near local midnight.

Frank, L. A.↗