Background density channel generation by axial plasma jets

The supersonic expansion of a dense plasma into an ambient plasma can be observed in phenomena ranging from coronal mass ejections and protostellar outflows to astrophysical jets. To produce a supersonic plasma jet in a laboratory setting, a laser-produced plasma explodes into an ambient argon plasma ($n\sim5\cdot10^{12}cm^{-3}$,$c_{s}\sim6\cdot10^{5}cm/s$,$v_{A}\sim1.2\cdot10^{7}cm/s$) in the Large Plasma Device at UCLA. This study focuses on the initial formation and evolution of the jet and its effects on the background magnetized plasma. Using a laser-induced fluorescence diagnostic of Ar-II ions at their 611.5nm transition, the jet is seen to perturb the equilibrium population of the target argon ions. A CCD camera with a fast ($\geq3$ns) shutter spatially and temporally resolves images of the fluorescence. Time-lapsed imaging shows an axially aligned channel of depleted fluorescence form near the source and travel with an undiminished speed characteristic of the jet ($v/c_{s}\sim20$) while remaining highly collimated. Langmuir probe measurements show a large ion flux moving in conjunction with the excited argon depletion after traveling more than an ion inertial length.