Observation of Kinetic Plasma Jets in a Coronal-Loop Simulation Experiment

Under certain conditions an intense kinetic plasma jet is observed to emerge from the apex of laboratory simulations of coronal plasma loops. Analytic and numerical models show that these jets result from a particle orbit instability in a helical magnetic field whereby magnetic forces radially eject rather than confine ions with sufficiently large countercurrent axial velocity.

Figure 1

Kinetic plasma jet emanating from an argon laboratory loop. Dashed arch corresponds to initial plasma loop at $t\approx 1.0\mu \mathrm{s}$ as in Fig. 4b. Arrows represent lines of sight (los #) used for spectroscopy; arrow widths represent $\sim 6\mathrm{mm}$ diameter of lines of sight.

Figure 2

(a) Flux tube geometry used in the model. (b) Experimental configuration; $B$ outside the flux loop is weakest on the right-hand side (indicated as weak field region).

Figure 3

(a) $S=1.5$ gives “valley” (i.e., stable) effective potential $V(\xi )$ while $S=-0.5$ gives “hill” (i.e., unstable). (b) Numerically calculated particle trajectories. (c) Probe measurement of flux tube magnetic field showing that field is weak on right side as sketched in Fig. 2b.

Figure 4

Evolution of laboratory plasma loops at (a) high $M_n$, (b) low $M_n$, and (c) low $\Phi$. Movies placed in Ref. 13 show the evolutions even more dramatically.

Figure 5

Measured spectra of an ${\mathrm{Ar}}^{+}$ line (rest-frame wavelength ${\lambda }_0=434.806\mathrm{nm}$ shown by vertical lines). Velocity is $v=c(\lambda -{\lambda }_0)/{\lambda }_0$ where $\lambda$ is measurement wavelength, $c$ is speed of light. Lines of sight (los #) are shown in Fig. 1. (a) Spectra from the cathode (los #1) and anode (los #2) regions for $t=0–0.5\mu \mathrm{s}$. (b) Spectra from the kinetic jet region along los #3, #4, and #5 for $t=2.5–5.5\mu \mathrm{s}$, $7.0–9.0\mu \mathrm{s}$, and $6.0–18.0\mu \mathrm{s}$, respectively.

Figure 6

Measured $S$ for various plasma configurations. Solid (open) symbols represent high (low) $M_n$ respectively, number of sides in symbols represent capacitor charging voltage in kV, and arrowheads indicate plasma shots where kinetic jets are observed. The existence of kinetic jets has an excellent correlation with $S$ being negative.