Hall currents in a current sheet: Structure and dynamics

Abstract

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.

Enhancement of the guide field during the current sheet formation in the three-dimensional magnetic configuration with an X line

“…More recently, it was established that the magnetic field of such a current sheet frequently takes on a 3D configuration due to generation of Hall currents [5][6][7][8][9][10][11][12][13][14][15]. Compared to the 2D case, the magnetic field structure becomes more complicated when the current sheet is produced in the initial 3D magnetic configuration, in the presence of the out-of-plane magnetic field component (guide field) aligned with the X line.…”

“…The regions of the excess guide field prove to be precisely the regions, where the main current aligned with the X line is localized. It should be pointed out that in this experiment, the guide field produced by the Hall currents is negligibly small because of appropriate choosing the instants of time and space positions for measurements (for details, see [15,28]). It is evident that an enhancement of the guide field is available because of appearance of the in-plane plasma currents.…”

Experimental Study of Current-Driven Turbulence During Magnetic Reconnection

“…More recently, however, experiments that are in an MHD regime (i.e. d i and ρ i much smaller than the device size) have been able to find these two-fluid effects within their current sheets [24][25][26]. Finally, these effects have also been found by spacecraft flying through reconnecting current sheets in the earth's magnetosphere [27].…”

Flare-type events and generation of plasma jets in current sheets evolving in laboratory conditions

“…The CS characteristic dimensions are: length Δz, width 2δx ≈ (8-12) cm, and thickness 2δy ≈ (1.5-3.5) cm. Plasma current concentration in the CS modifies the initial configuration (2.1): the tangential component B x increases significantly, while the normal component (Frank & Bogdanov 2001;Frank et al 2008Frank et al , 2009). The CS formation results also in effective plasma compression into the sheet, so that the electron density in the CS mid-plane increases up to (1-3)·10 16 cm −3 , i.e., it is 5-15 times the initial density (Bogdanov et al 2002;Frank et al 2005).…”

“…The pressure gradient impedes compression and the CS formation brings about the establishment of transverse equilibrium. The pressure gradient is negligible along the CS surface (x-axis), whereas the Ampere forces are of crucial importance for the Hall current excitation (Frank et al 2008) and the generation of plasma jets (Kyrie et al 2010). The Ampere force [j × B] x along the CS width is determined by current j z and normal component B y , which is usually nonzero in the metastable CS (Fig.…”