[1] In this paper we investigate intense (with current density larger than 15 nA/m 2 ) thin (thickness is less than proton gyroradius) horizontal current sheets observed by Cluster in 2003 year in the Earth magnetotail. We compare observed profiles of the curlometer current density with particle currents and analytical estimates. We show that intense horizontal current sheets represent a particular class of current sheets where the almost all current density can be described by electron curvature currents. Intensification of these currents is provided by increase of the electron temperature anisotropy in the central region of current sheets where parallel/antiparallel electron beams are found. The substantial part of the vertical pressure balance in such intense sheets can be supported by the local increase of the shear component of the magnetic field. We show that this is common property for intense current sheets observed in the magnetotail and in the laboratory experiments. The later measurements can help in understanding particular details, since spacecraft observations of such current sheets are relatively rare, especially due to their relation to localized active regions.
The formation and evolution of the plasma sheets resulting from the plasma compression in diversified three-dimensional (3D) magnetic configurations with singular X lines are reported on. The research was focused on the correlation between the structure of a plasma sheet and the topology of the initial 3D magnetic configuration, especially on the impact of the guide field aligned with the X line. It has been demonstrated experimentally that plasma compression and formation of extended plasma sheets can take place in configurations with the X lines in the presence of a strong guide field. The electron density distributions in the plasma sheets were found to be rather sensitive to the magnetic field topology. The experiments revealed the effect of progressive decrease of the plasma compression ratio in response to increasing guide field. This effect has two basic manifestations: a decrease of the maximum plasma density and an enlargement of the sheet thickness. Based on the experimental data we advanced a concept that the deterioration of plasma compression into the sheet is due to enhancement of the guide field inside the sheet over its initial value, and due to excitation of additional currents in the plane perpendicular to the singular X line and to the original current in the sheet.
Experimental results are presented from the study of the structure and time evolution of the Hall currents in the current sheets produced in the two-dimensional magnetic fields with the null line of the X type, in plasmas with heavy ions. Three-component magnetic fields generated by plasma currents were measured, and particular emphasis was placed on the out-of-plane magnetic field component aligned with the null line. The temporal evolution and spatial structure of the out-of-plane magnetic field and its dependence on the ion mass made us conclude that this field is produced by the Hall currents. The out-of-plane magnetic field is of the quadrupole structure, being directed oppositely on the opposite sides of the current sheet symmetry planes. The out-of-plane field exists at the initial stage of the sheet evolution, in a limited time interval, which is more prolonged for the sheets formed in plasmas with heavier ions. We revealed that the Hall currents of the opposite directions exist inside the current sheet, while the basic current has only one direction. Near the sheet middle plane the Hall currents flow from the peripheral regions toward the null line, whereas at larger distances from the middle plane the Hall currents become reversed. The Hall currents in both directions are localized only in the regions, where the basic current exists. At every time moment the oppositely directed Hall currents practically cancel each other and form four closed current circuits in the (x,y) plane, which produce the out-of-plane quadrupole magnetic field.
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