Supersonic Radiatively Cooled Rotating Flows and Jets in the Laboratory

The first laboratory astrophysics experiments to produce a radiatively cooled plasma jet with dynamically significant angular momentum are discussed. A new configuration of wire array $z$ pinch, the twisted conical wire array, is used to produce convergent plasma flows each rotating about the central axis. Collision of the flows produces a standing shock and jet that each have supersonic azimuthal velocities. By varying the twist angle of the array, the rotation velocity of the system can be controlled, with jet rotation velocities reaching $\sim 18\%$ of the propagation velocity.

Figure 1

Laser interferometry of (a) an untwisted conical wire array and (b) a conical wire array with a twist between the two electrodes $\Phi =2\pi /16$. The twist is seen to alter the conical shock on the axis of the array and the jet which propagates upwards, above the anode plate. The conical arrays consist of 16, $18\mu \mathrm{m}\mathrm{W}$ wires with 30° wire inclination angles.

Figure 2

Time gated XUV (top, $h\nu >30\mathrm{eV}$) and soft x-ray (bottom, $h\nu >220\mathrm{eV}$) self-emission images taken end-on to the array at $\sim 210\mathrm{ns}$ after the start of current. This rotation angle of the array $\Phi$ (defined on image (d)) is varied on the different images: (a) $\Phi =0$, (b) $\Phi =2\pi /64$, (c) $\Phi =2\pi /32$, and (d) $\Phi =2\pi /16$.

Figure 3

Measurements of the conical shock diameter from experiments are plotted (a) at 210 ns (squares), with the limits indicating the thickness of the wall of the shock. The line on the plot represents the predictions of the shock model described in the text using the parameters defined in (b). The axis along the top of the plot is the angle of the streams used to fit the model to the data. Triangles on the plot show the position of peak density from MHD simulations described later in the text.

Figure 4

Schlieren images of jets from conical wire arrays. (a) Shows filament like structures, which rotate around the jet for a twist angle of $\Phi =2\pi /16$. Also shown are schlieren images of the base of jets with (b) $\Phi =0$, (c) $\Phi =2\pi /64$ and (d) $\Phi =2\pi /16$. All images are at $t=315–340\mathrm{ns}$ after start of the current.

Figure 5

Results of MHD simulations. (a) Isodensity surfaces at 270 ns show the dense plasma around the wires (${10}^{-3}\mathrm{g}/{\mathrm{cm}}^3$, (dark gray) and plasma streams ($2.5\times {10}^{-5}\mathrm{g}/{\mathrm{cm}}^3$, light gray); streamlines from one of the wires are shown with the oppositely rotating flows separated visually by red and orange streamlines; the azimuthally averaged poloidal magnetic filed lines are shown in blue. (b) Azimuthally averaged profiles of azimuthal velocity, density, and temperature taken 6 mm above the cathode at 200 ns.