| 1. |
- Bohm, Martin, et al.
(författare)
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Dynamic trapping : Neutralization of positive space charge in a collisionless magnetized plasma
- 1990
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Ingår i: Physical Review Letters. - 0031-9007. ; 65, s. 859-866
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Tidskriftsartikel (refereegranskat)abstract
- It is shown by numerical simulations that in a collisionless plasma electron inertia leads to inefficient neutralization of positive space charge and allows large positive potentials (φ ≫ kTe/e) to be established and maintained on the time scale of ion motion. This is true even if the buildup of positive space charge is so slow that it corresponds to a small fraction of the random electron current of the surrounding plasma. A simple physical model clarifies the physics of the process and provides an analytical expression for the potential.
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| 2. |
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| 3. |
- Bohm, Martin, et al.
(författare)
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Dynamic trapping of electrons in the porcupine ionospheric ion beam experiment
- 1992
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Ingår i: Advances in Space Research. - 0273-1177. ; 12, s. 9-14
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Tidskriftsartikel (refereegranskat)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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| 4. |
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| 5. |
- Brenning, Nils, et al.
(författare)
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Critical ionization velocity interaction in the CRIT I rocket experiment
- 1990
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Ingår i: Advances in Space Research. - : Elsevier BV. - 0273-1177. ; 10, s. 63-66
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Brenning, Nils, et al.
(författare)
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Dynamic trapping and skidding of dense plasma clouds
- 2004
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 70:03-feb, s. 153-156
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the possibility that the mechanism dynamic trapping can play a role in decoupling dense plasma clouds injected in a thinner ambient plasma, by establishing strong magnetic-field-aligned electric fields in the vicinity or in the edge of the cloud. Dynamic trapping has previously been shown to allow such fields to be established and maintained on the time scale of ion motion, also for arbitrarily low current densities. A model is presented of how such fields could arise and decouple injected plasma clouds, a mechanism which we call dynamic decoupling. A dimensionless parameter. the dynamic decoupling factor F-DD, is derived which gives an estimate of the importance of the process. One possible application is the CRRES ionospheric injection experiments where anomalous skidding has recently been reported. However. the dynamic decoupling mechanism might also play a role in naturally occurring situations, e.g. the impulsive penetration of plasmoids from the solar wind into the Earth's magnetosphere.
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| 7. |
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| 8. |
- Brenning, Nils, et al.
(författare)
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Electrodynamic interaction between the CRIT I ionized barium streams and the ambient ionosphere
- 1990
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Ingår i: Advances in Space Research. - : Elsevier BV. - 0273-1177. ; 10, s. 67-70
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Brenning, Nils, et al.
(författare)
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Interpretation of the Electric Fields Measured in an Ionospheric Critical Ionization Velocity Experiment
- 1991
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 96, s. 9719-9733
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the quasi-dc electric fields measured in the CRIT I ionospheric release experiment, which was launched from Wallops Island on May 13, 1986. The purpose of the experiment was to study the critical ionization velocity (CIV) mechanism in the ionosphere. Two identical barium shaped charges were fired from distances of 1.99 km and 4.34 km towards a main payload, which made full three-dimensional measurements of the electric field inside the streams. There was also a subpayload separated from the main payload by a couple of kilometers along the magnetic field. The relevance of earlier proposed mechanisms for electron heating in CIV is investigated in the light of the CRIT I results. It is concluded that both the “homogeneous” and the “ionizing front” models probably apply, but in different parts of the stream. It is also possible that electrons are directly accelerated by a magnetic-field-aligned component of the electric field; the quasi-dc electric field observed within the streams had a large magnetic-field-aligned component, persisting on the time scale of the passage of the streams. The coupling between the ambient ionosphere and the ionized barium stream in CRIT I was more complicated than is usually assumed in CIV theories, with strong magnetic-field-aligned electric fields and probably current limitation as important processes. One interpretation of the quasi-dc electric field data is that the internal electric fields of the streams were not greatly modified by magnetic-field-aligned currents, i.e., a state was established where the transverse currents were to a first approximation divergence-free. It is argued that this interpretation can explain both a reversal of the strong explosion-directed electric field in burst 1 and the absence of such a reversal in burst 2.
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| 10. |
- Fälthammar, Carl-Gunne, et al.
(författare)
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Magnetosphere-ionosphere interactions as a key to the plasma Univers
- 1995
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Ingår i: IEEE Transactions on Plasma Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0093-3813 .- 1939-9375. ; 23, s. 2-9
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Tidskriftsartikel (refereegranskat)abstract
- Almost all known matter in the universe is in a state, the plasma state, that is rare on Earth, and whose physical properties are still incompletely understood. Its complexity is such that a reliable understanding must build on empirical knowledge. While laboratory experiments are still an important source of such knowledge, Earth’s magnetospere-ionosphere system, made accessible by space technology, vastly widens the parameter ranges in which plasma phenomena can be studied. This system contains all three main categories of plasma present in the universe. Furthermore, the interaction between the magnetosphere and the ionosphere excites a wealth of plasma physical phenomena of fundamental importance. These include, among others, formation of magnetic-field aligned electric fields, acceleration of charged particles, release of magnetically stored energy, formation of filamentary and cellular structures, as well as unexpected chemical separation processes. What has been learned, and what stilt remains to be learned, from study of the magnetosphere-ionosphere system should therefore provide a much improved basis for understanding of our universe.
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