| 1. |
- Brenning, Nils, et al.
(author)
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Conditions for plasmoid penetration across abrupt magnetic barriers
- 2005
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 12:1
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Journal article (peer-reviewed)abstract
- The penetration of plasma clouds, or plasmoids, across abrupt magnetic barriers (of the scale less than a few ion gyro radii, using the plasmoid directed velocity) is studied. The insight gained earlier, from detailed experimental and computer simulation investigations of a case study, is generalized into other parameter regimes. It is concluded for what parameters a plasi-noid should be expected to penetrate the magnetic barrier through self-polarization, penetrate through magnetic expulsion, or be rejected from the barrier. The scaling parameters are n(e), upsilon(o), B-perpendicular to, m(i), T-i, and the width w of the plasmoid. The scaling is based on a model for strongly driven, nonlinear magnetic field diffusion into a plasma which is a generalization of the earlier laboratory findings. The results are applied to experiments earlier reported in the literature, and also to the proposed application of impulsive penetration of plasmoids from the solar wind into the Earth's magnetosphere.
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| 2. |
- Hurtig, T., et al.
(author)
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The role of high frequency oscillations in the penetration of plasma clouds across magnetic boundaries
- 2005
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 12:1
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Journal article (peer-reviewed)abstract
- Experiments are reported where a collissionfree plasma cloud penetrates a magnetic barrier by self-polarization. Three closely related effects, all fundamental for the penetration mechanism, are studied quantitatively: (1) anomalous fast magnetic field penetration (two orders of magnitude faster than classical), (2) anomalous fast electron transport (three orders of magnitude faster than classical and two orders of magnitude faster than Bohm diffusion), and (3) the ion energy budget as ions enter the potential structure set up by the self-polarized plasma cloud. It is concluded that all three phenomena are closely related and that they are mediated by highly nonlinear oscillations in the lower hybrid range, driven by a strong diamagnetic current loop which is set up in the plasma in the penetration process. The fast magnetic field penetration occurs as a consequence of the anomalous resistivity caused by the wave field and the fast electron transport across magnetic field lines is caused by the correlation between electric field and density oscillations in the wave field. It is also found that ions do not lose energy in proportion to the potential hill they have to climb, rather they are transported against the dc potential structure by the same correlation that is responsible for the electron transport. The results obtained through direct measurements are compared to particle in cell simulations that reproduce most aspects of the high frequency wave field.
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| 3. |
- Karlsson, Tomas, et al.
(author)
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On enhanced aurora and low-altitude parallel electric fields
- 2005
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In: Physica Scripta. - 0031-8949 .- 1402-4896. ; 72:5, s. 419-422
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Journal article (peer-reviewed)abstract
- Enhanced auroras are bands of enhanced intensity, sometimes observed along the bottom edges of auroral arcs. It is here proposed that they sometimes are due to local electron energization by low-altitude. downward-directed DC electric fields. which arise as a consequence of the ionospheric response to small-scale auroral current systems. Simulations of such structures are presented. and the electron energization mechanism is discussed. The enhanced auroras would, in this model, appear parallel and close to (perhaps only a few kin front) an ordinary auroral arc. Detailcd 3-D observations of auroral arc structures could resolve if enhanced auroras sometimes take this form.
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