Structure of a Magnetic Flux Annihilation Layer Formed by the Collision of Supersonic, Magnetized Plasma Flows

We present experiments characterizing the detailed structure of a current layer, generated by the collision of two counterstreaming, supersonic and magnetized aluminum plasma flows. The antiparallel magnetic fields advected by the flows are found to be mutually annihilated inside the layer, giving rise to a bifurcated current structure—two narrow current sheets running along the outside surfaces of the layer. Measurements with Thomson scattering show a fast outflow of plasma along the layer and a high ion temperature ($T_i\sim \overline{Z}{T}_e$, with average ionization $\overline{Z}=7$). Analysis of the spatially resolved plasma parameters indicates that the advection and subsequent annihilation of the inflowing magnetic flux determines the structure of the layer, while the ion heating could be due to the development of kinetic, current-driven instabilities.

Figure 1

Cross-sectional schematic diagrams of the production of two magnetized, colliding plasma flows from (a) end and (b) side views. [(c) and (d)] Corresponding interferograms of the structure of the interaction region from each perspective (fields of view are indicated in schematics).

Figure 2

(a) End-on electron density map, obtained by interferometry, showing probing geometry of the TS laser beam, and positions (black dots, $A\text{−}C$) of TS measurements whose spectra are shown in Fig. 3. (b) TS geometry vector diagram.

Figure 3

[(a)–(c)] Fitted TS spectra for the three spatial points in the interaction region marked in Fig. 2. The dotted line (${\lambda }_0$) indicates spectrometer resolution. [(d) and (e)] Profiles of $V_y(x)$ and $T_i(x)$ measured in a single experiment for scattering volumes along the TS beam when passing through position $C$ in Fig. 2.

Figure 4

Side-on maps of the interaction region showing (a) the electron line density (interferometry), (b) Faraday rotation angle, and (c) magnetic field. Ring structures evident in the data are artifacts caused by dust spots.

Figure 5

(a) $z$-averaged profile of the measured (blue dots) magnetic field $B_y(x)$, and (b) profile of the current density calculated for a fitted magnetic field profile shown by the red dashed line in (a).