Soft x-ray laser interferometry/shadowgraphy of exploding wire plasmas

We present results from soft x-ray laser interferometry/shadowgraphy of current-driven thin wire plasmas using a capillary discharge pumped 46.9 nm laser and a diffraction grating interferometer. We have obtained series of soft x-ray images of exploding Al wires 15 μm or 25 μm in diameter. The high photo-ionization cross sections of atoms and low charge ions at this wavelength allow the soft x-ray laser probe to detect the early stages of formation of a coronal plasma surrounding the wire core. Wires of 25 μm diameter excited by current pulses with a 78 A/ns increase rate are observed to expand uniformly. However, an increase in the rate of energy deposited per unit of mass is observed to give rise to significant instabilities. The simultaneous analysis of the fringe shift and soft x-ray absorption data suggests the coronal plasma contains a significant concentration of low Z impurities. The results illustrate that table-top soft x-ray lasers are a powerful new tool for the diagnostics of dense plasmas.

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