Identification of a Quasiseparatrix Layer in a Reconnecting Laboratory Magnetoplasma

The concept of quasiseparatrix layers (QSLs) has emerged as a powerful tool to study the connectivity of magnetic field lines undergoing magnetic reconnection in solar flares. Although they have been used principally by the solar physics community until now, QSLs can be employed to shed light on all processes in which reconnection occurs. We present the first application of this theory to an experimental flux rope configuration. The three-dimensional data set acquired in this experiment makes the determination of the QSL possible.

Figure 1

Schematic of experiment (not to vertical scale). The background He plasma is produced by a BaO coated cathode that is biased to a mesh anode by a transistor-switched capacitor bank. The ${\mathrm{LaB}}_6$ cathodes, pulsed by a separate capacitor bank, produce the flux ropes.

Figure 2

(a) Typical current in ${\mathrm{LaB}}_6$-mesh anode circuit. (b) $B_x$ at (0.0, 2.7, 64) cm, which is at the edge of the lower flux rope, and (c) ($-1.5$, 9.9, 830) cm, showing pulses due to the rotation of the flux ropes at the far end.

Figure 3

(a) Two sets of representative field lines at $t=1.615\mathrm{ms}$. The field lines are seeded from a 1.0 cm diameter circle centered at each current channel in the $z=64\mathrm{cm}$ plane. The axial dimension is compressed 30 times. (b) $J_z$ at each end plane at an early time (top row) and at a late time (bottom row) in the discharge.

Figure 4

Hodograms of the point at which the central field line in each flux rope intersects (a) the $z=600\mathrm{cm}$ plane and (b) the $z=830\mathrm{cm}$ plane. “Upper” and “lower” indicate which cathode the field line is seeded from. Each arrow indicates the start of the hodogram at $t=1610\mathrm{ms}$. (c) Distance $\Delta s$ between each flux rope at each axial position.

Figure 5

A logarithmic plot of the squashing degree $Q$ in the $z=64\mathrm{cm}$ plane at $t=1.699\mathrm{ms}$. Isocontours of $J_z=\{-5.5,-3.0\}\mathrm{A}/{\mathrm{cm}}^2$ are overplotted in white.

Figure 6

(a) Representative field lines from each flux rope with the $Q=1000$ surface in blue threading between them at $t=1.699\mathrm{ms}$. The field lines are seeded from the same locations as in Fig. 3. The axial dimension is compressed 30 times. (b) A view of the QSL and its hyperbolic flux tube structure. Field lines in red and yellow are seeded from the upper and lower sides of the QSL, respectively. Each pair of field lines is initially separated by the QSL width, 0.05 cm, but diverge to either corner of the QSL ($\sim 2\mathrm{cm}$ separation) in the $z=830\mathrm{cm}$ plane. The axial dimension is compressed 100 times.