Study of the stagnated plasma generated from the head-on collision of two plasma jets*

We were studying the dynamics of stagnated plasma generated from the head-on collision of two plasma jets. To generate the stagnated plasma in the laboratory, two counter-streaming plasma jets were first generated by a bi-conical-wire array driven by a 1-kJ pulsed-power system. The bi-conical-wire array consisted of two identical conical-wire arrays facing against each other. Each of them was made of four tungsten wires with a diameter of 20 μm. The inclination angle, the diameter of the bottom and the height of conical-wire arrays were 30°, 5 mm, and 10 mm, respectively. When the pulsed current with a peak of ∼123.5 kA and a rise time of ∼1.6 μs flew through the bi-conical-wire array, the tungsten wires were vaporized and ionized by the current via ohmic heating. The azimuthal magnetic field generated by the current pushed the tungsten plasma toward the center. Counter-streaming plasma jets were generated when the plasma merged on the axis of the bi-conical-wire array. Finally, the plasma stagnated at the center of the bi-conical-wire array when two plasma jets collided with each other. To observe the stagnated plasma, a suite of time-resolved optical diagnostics using a 5-ns Q-switch laser in 532 nm was implemented. It included an interferometer, a shadowgraph image, and a schlieren image for measuring the density, size, and velocity of the stagnated plasma. Density measurements showed that plasma started to stagnate at the center after ∼600 ns and reached a density of ∼10¹⁶ cm^-3. Experimental results will be given.