Interaction of a converging shock wave with a plasma

Summary form only given. Experimental studies of a spherical converging shock wave (SW) interaction with preliminary formed plasma are presented. The SW was generated by an underwater electrical explosion of a spherical Cu wire array (radius of 15 mm, number of wires of 40, and wire diameter of 0.1 mm) supplied by 240-kA amplitude current pulse with rise time of ~0.8 μs. The plasma was formed by a 40 Pa propane discharge between the cathode and anode electrodes, placed at the distance of 1.5 mm apart, inside of 2 mm inner diameter quartz capillary located at the equatorial plane of the array. The light emission from the plasma was transferred to the inputs of two spectrometers by optical fiber installed from the one side of the capillary and beam splitter with lenses. The spectral lines intensities at the output of spectrometers were recorded prior and during the SW interaction with plasma by intensified framing 4QuikE cameras and by a photomultiplier tube when one of the spectrometers was used as a monochromator. Hα and Hβ spectral lines and line-to-continuum ratios, combined with the ratio of relative intensities of C III/C II and Si III/Si II lines, were used to determine the plasma density and temperature evolution. It was found that during the first -200 ns with respect to the beginning of the plasma compression by the SW, the plasma density increases from 2×10 ¹⁷ cm ^-3 to 5×10 ¹⁸ cm ^-3 while the plasma temperature remained almost unchanged, 3-4 eV. Further, following a model of an adiabatically imploding capillary, the plasma density increases >1019 cm ^-3 , resulting in continuum spectrum obtained in the experiment with temperature exceeding 50 eV at radii of compression ≤50 μm.