| 1. |
- Bohm, Martin, et al.
(author)
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Dynamic trapping of electrons in the porcupine ionospheric ion beam experiment
- 1992
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In: Advances in Space Research. - 0273-1177. ; 12, s. 9-14
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Journal article (peer-reviewed)abstract
- Electrons are needed to maintain quasineutrality in a case where positive ions are injected across the magnetic field into a limited volume in a magnetized plasma. In the absence of collisions, a positive potential builds up and traps the electrons which enter the region along the magnetic field. If the added density of ions exceeds the ambient density, large potential differences along the magnetic field can be maintained this way. The process explains several features of the Porcupine xenon ion beam injection experiment, where strong magnetic-field-aligned electric fields were measured in the vicinity of a xenon ion beam which was injected into the ambient ionosphere from a spinning subpayload. © 1992.
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| 2. |
- Brenning, Nils, et al.
(author)
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Critical ionization velocity interaction in the CRIT I rocket experiment
- 1990
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In: Advances in Space Research. - : Elsevier BV. - 0273-1177. ; 10, s. 63-66
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Journal article (peer-reviewed)abstract
- In the rocket experiment CRIT I, launched from Wallops Island on 13 May 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. © 1989.
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| 3. |
- Brenning, Nils, et al.
(author)
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Electrodynamic interaction between the CRIT I ionized barium streams and the ambient ionosphere
- 1990
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In: Advances in Space Research. - : Elsevier BV. - 0273-1177. ; 10, s. 67-70
-
Journal article (peer-reviewed)abstract
- In the CRIT I Critical Velocity experiment, launched from Wallops Island on 13 May, 1986, two fast barium streams were ejected by means of shaped charges. Their electrodynamic interaction with the ambient ionosphere is discussed. An outstanding feature of the DC electric field observed within the streams was a large magnetic-field-aligned component, persisting on the time scale of the passage of the streams. One interpretation of the DC electric field data is that the internal electric fields of the streams is not greatly modified by Birkeland currents, i.e. a state is established, where the transverse currents are to a first approximation divergence-free. It is argued that this interpretation can explain why a reversal of the strong explosion-directed electric field was observed in the first explosion but not in the second (more distant one). © 1989.
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| 4. |
- Ekbom, L. B., et al.
(author)
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Liquid phase sintering of tungsten composites under microgravity : Influence of liquid/particle surface energy
- 1991
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In: Advances in Space Research. - 0273-1177 .- 1879-1948. ; 11:7, s. 331-335
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Journal article (peer-reviewed)abstract
- Tungsten-nickel-iron heavy metals are fabricated from powders by liquid phase sintering. A study of the sintering mechanism of heavy metals with a low amount of tungsten particles can, depending on sedimentation, only be done under microgravity. At two earlier Texus flights, No 10 & 19, the growth rate and agglomeration of tungsten particles under microgravity were compared to that under gravity and sedimentation. During the first minute sintering period the particles in the agglomerates were separated and the particle distribution became even. The particle growth rate under microgravity, initially high, is slowing down. At further studies under gravity the influence of surface energy between the liquid phase and the tungsten particles have been investigated. Additions of sulphur and cobolt were used to decrease the surface energy and the use of nickel without iron to increase the energy. At a high surface energy the growth rate increases due to increased driving force. Preliminary results from the Texus 26 flight (April 90) are included. © 1991.
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