Plasmoid Ejection and Secondary Current Sheet Generation from Magnetic Reconnection in Laser-Plasma Interaction

Reconnection of the self-generated magnetic fields in laser-plasma interaction was first investigated experimentally by Nilson et al. [Phys. Rev. Lett. 97, 255001 (2006)] by shining two laser pulses a distance apart on a solid target layer. An elongated current sheet (CS) was observed in the plasma between the two laser spots. In order to more closely model magnetotail reconnection, here two side-by-side thin target layers, instead of a single one, are used. It is found that at one end of the elongated CS a fanlike electron outflow region including three well-collimated electron jets appears. The ($>1\mathrm{MeV}$) tail of the jet energy distribution exhibits a power-law scaling. The enhanced electron acceleration is attributed to the intense inductive electric field in the narrow electron dominated reconnection region, as well as additional acceleration as they are trapped inside the rapidly moving plasmoid formed in and ejected from the CS. The ejection also induces a secondary CS.

Figure 1

Interferometric image at $t=t_0\mathrm{ns}$ (a) and $t=t_0+1\mathrm{ns}$ (b), where $t_0$ is set at the half maximum of the laser-pulse tail. The electron diffusion region is between X1 and X2. F marks the edge of the advecting plasma. P1 and P2 (1.16 and 1.75 mm from X2, respectively) mark the location of a front of the expanding fanlike region at the two times, from which an outflow speed of $>600\mathrm{km}/\mathrm{s}$ is estimated. The angle of the fanlike plasma region is 35°–40°. (c) Linearly polarized self-emission image of the plasma. (d) PIC simulation result showing the current density, typical field lines, the secondary CS, and a plasmoid. (e) Schematic illustration of (c). The short thick (red) arrows indicate the plasma inflow directions for the primary and secondary CS.

Figure 2

A typical x-ray pinhole image, with superimposed schematics of the experimental setup, and the corresponding intensity curves at two locations. The x-ray emission is strongest in the electron diffusion region at the center and is of width $\sim 85\mu \mathrm{m}$. The two central emission peaks in the L2 profile correspond to the two edge electron jets at the start of the fanlike region.

Figure 3

Spatially resolved emission of $K\alpha$ lines from heliumlike ions and the satellite lines from (a) the Ti wire and (c) the Al targets. (b) and (d) Typical line spectra from Ti and Al, respectively, together with the results calculated by using a nonlocal thermodynamic equilibrium model. (e) Local Al plasma electron density and temperature estimated from (d). The solid and dashed lines show the plasma electron density and temperature, respectively, obtained from a hydrodynamic code. The sketch shows the relevant experimental components.