Engineering topics

Haerendel, G.

Publications and source records attributed to Haerendel, G..

At least 19 records

NASA NTRS1997

The Electron Drift Instrument for Cluster

The Electron Drift Instrument (EDI) measures the drift of a weak beam of test electrons that, when emitted in certain directions, return to the spacecraft after one or more gyrations. This drift is related to the electric field and the gradient in the magnetic field, and these quantities can, by use of different electron energies, be determined separately. As a by-product, the magnetic field strength is also measured. The present paper describes the scientific objectives, the experimental method, and the technical realization of the various elements of the instrument.

Paschmann, G.↗

NASA NTRS1991

Interpretation of the electric fields measured in an ionospheric critical ionization velocity experiment

The quasi-dc electric fields measured in the CRIT I ionospheric release experiment are studied. In the experiment, two identical barium shaped charges were fired toward a main payload, and three-dimensional measurements of the electric field inside the streams were made. The relevance of proposed mechanisms for electron heating in the critical ionization velocity (CIV) mechanism is addressed. It is concluded that both the 'homogeneous' and the 'ionizing front' models probably are valid, but in different parts of the streams. It is also possible that electrons are directly accelerated by a magnetic field-aligned component of the electric field. The coupling between the ambient ionosphere and the ionized barium stream is more complicated that is usually assumed in CIV theories, with strong magnetic-field-aligned electric fields and probably current limitation as important processes.

Brenning, N.↗

NASA NTRS1990

Optical observations on the CRIT-II Critical Ionization Velocity Experiment

A rocket borne Critical Ionization Velocity (CIV0 experiment was carried out from Wallops Island at dusk on May 4, 1989. Two barium shaped charges were released below the solar terminator (to prevent photoionization) at altitudes near 400 km. The ambient ionospheric electron density was 50,000/cu cm. The neutral barium jet was directed upward and at an angle of nominally 45 degrees to B which gives approximately 3 x 10 to the 23rd neutrals with super critical velocity. Ions created by a CIV process in the region of the neutral jet would travel up along B into sunlight where they can be detected optically. Well defined ion clouds (max. brightness 750 R) were observed in both releases. An ionization rate of 0.8 percent/sec (125 sec ionization time constant) can account for the observed ion cloud near the release field line, but the ionization rate falls off with increasing distance from the release. It is concluded that a CIV process was present in the neutral jet out to about 50 km from the release, which is significantly further than allowed by current theories.

Stenbaek-Nielsen, H. C.↗

NASA NTRS1990

Critical ionization velocity interaction in the CRIT I rocket experiment

In the rocket experiment CRIT I, launched from Wallops Island on May 13, 1986, two identical Barium-shaped charges were fired from distances of 1.3 km and 3.6 km towards the main experiment payload, which was separated from a sub-payload by a couple of km along the magnetic field. The relevance of earlier proposed mechanisms for electron heating in ionospheric critical velocity experiments is investigated in the light of the CRIT I results. It is concluded that both the 'homogeneous' and the 'ionizing front' models can be applied, in different parts of the stream. It is also possible that a third, entirely different, mechanism may contribute to the electron heating. This mechanism involves direct energization of electrons in the magnetic-field-aligned component of the dc electric field.

Brenning, N.↗

NASA NTRS1989

Dynamics of a barium release in the magnetospheric tail

The late time behavior of the May 13, 1985 magnetotail barium cloud is examined. The bulk dynamics of the cloud are studied based on triangulated data and data from Fabry-Perot Doppler velocity measurements. The changes in cloud morphology in relation to the in situ measurements made by the Ion Release Module satellite are discussed.

Mende, S. B.↗

NASA NTRS1987

Observations and theory of the AMPTE magnetotail barium releases

The barium releases in the magnetotail during the Active Magnetospheric Particle Tracer Explorers (AMPTE) operation were monitored by ground-based imagers and by instruments on the Ion Release Module. After each release, the data show the formation of a structured diamagnetic cavity. The cavity grows until the dynamic pressure of the expanding ions balances the magnetic pressure on its surface. The magnetic field inside the cavity is zero. The barium ions collect on the surface of the cavity, producing a shell. Plasma irregularities form along magnetic field lines draped over the surface of the cavity. The scale size of the irregularities is nearly equal to the thickness of the shell. The evolution and structuring of the diamagnetic cavity are modeled using magnetohydrodynamics theory.

Bernhardt, P. A.↗

NASA NTRS1987

AMPTE IRM observations of waves associated with flux transfer events in the magnetosphere

The AMPTE IRM wave instrument has been applied to the study of flux transfer events (FTE's). This initial investigation concentrates on FTE's observed in the magnetosphere during the fall of 1984. The wave morphology consists of four significant features: at frequencies below the ion gyrofrequency, magnetic fluctuations occur with amplitudes of the order of 1 nT; at frequencies from a few hertz to a few hundred hertz, electric field fluctuations are observed which have a broadband amplitude of a few millivolts per meter, which are perpendicularly polarized at the lowest frequencies, and which are partly electrostatic and partly electromagnetic; in the frequency range from 100 Hz to 10 kHz, broadband spikelike waves occur with a time-averaged amplitude of about 0.1 mV/m; and near the electron plasma frequency, bursts of waves occur at the boundaries of FTE's. In none of the 25 events surveyed does the total broadband amplitude of all the waves exceed a few millivolts per meter, an amplitude far too small to provide the dissipation required by 'traditional' reconnection models in which the dissipation region has a thickness the order of an ion gyroradius. Thus, either all of the FTE's are observed at some distance from the diffusion region, or the observable waves play no significant role in the diffusion process, or 'traditional' reconnection models do not apply to reconnection in FTE's.

Labelle, J.↗

NASA NTRS1987

Observation of nonlinear wave decay processes in the solar wind by the AMPTE IRM plasma wave experiment

Nonlinear wave decay processes have been detected in the solar wind by the plasma wave experiment aboard the Active Magnetospheric Particle Tracer Explorers (AMPTE) IRM spacecraft. The main process is the generation of ultralow-frequency ion acoustic waves from the decay of Langmuir waves near the electron plasma frequency. Frequently, this is accompanied by an enhancement of emissions near twice the plasma frequency. This enhancement is most likely due to the generation of electromagnetic waves from the coalescence of two Langmuir waves. These processes occur within the electron foreshock in front of the earth's bow shock.

Koons, H. C.↗

NASA NTRS1986

Electric field measurements during the Condor critical velocity experiment

The instrumentation of the Condor critical velocity Ba experiment (Wescott et al., 1986) for the measurements of the energetic particles and the electric field associated with a Ba explosion is described. The Ba explosion created a complex electric field pulse detected in situ by a single-axis double electric-field probe on a separate spacecraft. The measurements provide evidence of several important links in the critical-velocity chain, and are consistent with two hypotheses. The first hypothesis involves the creation of large polarization electric field due to charge separation; the second hypothesis implies a polarization of the beam by currents flowing across it. The chain of physical processes inferred from the observations is in agreement with most theories for the Alfven process.

Kelley, M. C.↗

NASA NTRS1986

Waves and electric fields associated with the first AMPTE artificial comet

The solar-wind Ba release experiment with the Active Magnetospheric Particle Tracer Explorers is discussed. The explosion of the two Ba-containing canisters produced a rapidly expanding cloud of neutral Ba, which was rapidly ionized by the UV radiation from the sun. A static electric field of about 1-2 mV/m was detected inside the diamagnetic cavity created by the ion cloud. This field is in the same direction as the solar-wind electric field, suggesting that this field may be able to penetrate into the cloud. Electrostatic emissions were observed inside the diamagnetic cavity at the Ba ion plasma frequency.

Gurnett, D. A.↗

NASA NTRS1986

Plasma waves associated with the first AMPTE magnetotail barium release

Plasma waves observed during the March 21, 1985, AMPTE magnetotail barium release are described. Electron plasma oscillations provided local measurements of the plasma density during both the expansion and decay phases. Immediately after the explosion, the electron density reached a peak of about 400,000/cu cm, and then started decreasing approximately as t to the -2.4 as the cloud expanded. About 6 minutes after the explosion, the electron density suddenly began to increase, reached a secondary peak of about 240/cu cm, and then slowly decayed down to the preevent level over a period of about 15 minutes. The density increase is believed to be caused by the collapse of the ion cloud into the diamagnetic cavity created by the initial expansion. The plasma wave intensities observed during the entire event were quite low. In the diamagnetic cavity, electrostatic emissions were observed near the barium ion plasma frequency, and in another band at lower frequencies. A broadband burst of electrostatic noise was also observed at the boundary of the diamagnetic cavity. Except for electron plasma oscillations, no significant wave activity was observed outside of the diamagnetic cavity.

Gurnett, D. A.↗

NASA NTRS1986

Analysis and interpretation of the shocklike electrostatic noise observed during the AMPTE solar wind lithium releases

During the AMPTE (Active Magnetospheric Particle Tracer Explorers) solar wind lithium release on September 11, and again on September 20, 1984, an intense burst of electrostatic noise was observed near the upstream edge of the ion cloud. Comparisons with measurements by the IMP-6 and ISEE-1 spacecraft show that the spectrum and overall features of this noise are very similar to electrostatic noise observed at the Earth's bow shock. A stability analysis using realistic parameters shows that the electrostatic noise can be accounted for by an ion beam-plasma instability caused by the solar wind proton beam streaming through the nearly stationary lithium cloud. The growth rate of this instability is largest when the ion density and solar wind proton density are similar, which explains why the noise only occurs near the outer edge of the ion cloud. The similarity to the noise in the Earth's bow shock suggest that a shock may exist in the solar wind plasma flow upstream of the ion cloud. If the noise is associated with a shock, then it must be an electrostatic shock, since the ion cyclotron radii are too small for the existence of a MHD shock. Since the electrostatic instability occurs at phase velocities near the lithium thermal velocity, the electrostatic turbulence may play a role in heating the lithium ions and transferring momentum from the solar wind to the ion cloud.

Gurnett, D. A.↗

NASA NTRS1986

AMPTE lithium tracer releases in the solar wind - Observations inside the magnetosphere

The transfer of mass from the solar wind to the magnetosphere and its transport and energization within the magnetosphere are investigated. Lithium atoms released on September 11 and 20, 1984 are utilized as the tracers in this study. The components and capabilities of the Charge Composition Explorer, which are to measure magnetospheric ion composition, are described. The data collected is analyzed and it is observed that Li ions did not enter the magnetosphere in sufficient quantities to be distinguished from the background particles. The modeling of solar wind and magnetosheath transport of Li ions is examined; more than 20 percent of the Li released on September 11, and 50 percent of the Li released on September 20 are mapped to the area around the stagnation point of the magnetopause.

Krimigis, S. M.↗

NASA NTRS1986

Observations of the artificially injected Porcupine xenon ion beam in the ionosphere

Results are given of ion beam injection experiments performed in the auroral ionosphere in connection with the German Sounding Rocket Project Porcupine. A heavy (xenon) ion beam was injected into the collisionless ionospheric plasma approximately perpendicular to the ambient magnetic field at altitudes from 190 km to about 450 km. The beam propagates nearly undistorted across the plasma because it is essentially depolarized; at the same time the beam is not current neutralized. This unexpected behavior poses the interconnected problems of how the beam manages to become charge neutralized, how current closure is maintained, and what is the mechanism of depolarization.

Haeusler, B.↗

NASA NTRS1986

Solar wind-plasma interaction - The AMPTE solar wind plasma releases

A summary is given of the most important effects observed during the 3 AMPTE solar wind ion releases. Some of these effects may be of relevance in comparable astrophysical situations when large amounts of matter are injected into an ambient magnetized plasma streaming with a velocity much larger than the sonic and Alfvenic Mach numbers. For detailed presentations the reader is referred to the original publications listed in the References.

Bauer, O. H.↗

NASA NTRS1986

Electron plasma waves in the solar wind - AMPTE/IRM and UKS observations

Selected events of plasma wave and electromagnetic emissions in the earth's electron fore-shock region have been studied. Strong emissions are observed in the plasma-wave band when the site of the satellite is magnetically connected to the bow shock. These emissions are generally highly fluctuating. Under certain conditions one observes electromagnetic radiation at the second harmonic produced locally. Electromagnetic emission generated at a position far away from the site of the spacecraft is occasionally detected giving rise to remote sensing of the bow shock. These emissions are related to energetic electron fluxes.

Treumann, R. A.↗

NASA NTRS1985

Plasma waves associated with the AMPTE artificial comet

Numerous plasma wave effects were detected by the AMPTE/IRM spacecraft during the artificial comet experiment on December 27, 1984. As the barium ion cloud produced by the explosion expanded over the spacecraft, emissions at the electron plasma frequency and ion plasma frequency provided a determination of the local electron density. The electron density in the diamagnetic cavity produced by the ion cloud reached a peak of more than 5 x 10 to the 5th per cu cm, then decayed smoothly as the cloud expanded, varying approximately as t exp-2. As the cloud began to move due to interactions with the solar wind, a region of compressed plasma was encountered on the upstream side of the diamagnetic cavity. The peak electron density in the compression region was about 1.5 x 10 to the 4th per cu cm. Later, a very intense (140 mVolt/m) broadband burst of electrostatic noise was encountered on the sunward side of the compression region. This noise has characteristics very similar to noise observed in the earth's bow shock, and is believed to be a shocklike interaction produced by an ion beam-plasma instability between the nearly stationary barium ions and the streaming solar wind protons.

Gurnett, D. A.↗

NASA NTRS1985

Outline of the Active Magnetospheric Particle Tracer Explorers (AMPTE) mission

This paper is intended as an introduction to a series of papers describing the three satellites of the AMPTE mission and their instrumentation. The aims and scientific context of the program are given together with a comparison of the general characteristics of the three spacecraft and their orbits. There is a brief resume of the studies performed so far, and a statement of future plans, together with a calendar of completed and planned experiments and measurements.

Bryant, D. A.↗