In this paper we report on the ability of a compact current driver yielding 250 kA in 150 ns to produce counter-propagating plasma flows. The flows were produced by two vertically-opposed conical wire arrays separated by 1 cm, each comprised of 8 wires. With this array configuration, we were able to produce two supersonic plasma jets with velocities on the order of 100-200 km/s that propagate towards each other and collide. Aluminum wires were tested first; we observed a shock wave forming at the collision region that remained stationary for an extended period of time (~ 50 ns) using optical probing diagnostics and Extreme Ultraviolet imaging. After this period, a bow shock is formed that propagates at 20 km/s towards the cathode of the array, likely due to small differences in the density and/or speed of the jets. The inter-jet ion mean free path was estimated to be larger than the shock scale length for aluminum, indicating that the shock is not mediated by collisions, but possibly by a magnetic field, whose potential sources are also discussed. Radiative cooling and density contrast between the jets were found to be important in the shock wave dynamics. We studied the importance of these effects by colliding jets of two different materials, using aluminum in one and copper in the other. In this configuration, the bow shock was observed to collapse into a thin shell and then to fragment, forming clumpy features. Simultaneously, the tip of the bow shock is seen to narrow as the bow shock moves at a similar speed observed in the Al-Al case. We discuss the similarity criteria for scaling astrophysical objects to the laboratory, finding that the dimensionless numbers are promising.
We report on experiments examining the dynamics of low current (25 kA), long rise-time (400 ns) X-pinches. The experiments used two- and four-wire 5 μm tungsten X-pinches. We discuss coronal plasma dynamics, X-ray emission, cross-point evolution, and axial column dynamics. We show that the pinch dynamics are akin to those in X-pinches driven by 0.1–1 MA and at rise-rates from 0.25 to 10 kA/ns. We observe soft X-rays (∼1–2 keV range) emitted from the cross point in both two-wire and four-wire X-pinches at about peak current. These results show that compact current generators consisting of 2–4 small capacitors in a simple capacitive discharge circuit can produce good quality pinches for applications in Thomson X-ray scattering and backlighting among others.
We report on results from experiments using laser-cut X shaped foils (or foil X-pinches) driven by the 250 kA, 150 ns rise-time GenASIS Linear Transformer Driver. Optical probing of the laser-cut foil X-pinches shows considerable dynamic and qualitative similarity with the more traditional wire X-pinches. Results demonstrate excellent quality X-ray emission flux, timing, and source size. The foil X-pinches offer advantages such as improved, reproducible cross-point symmetry, and the opportunity for rep-rated operation, which is not possible with conventional X-pinches using wires.
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