The report presents the results from experimental investigation of micropinch formation in the plasma of a vacuum discharge induced by a 6 ns laser pulse of energy J = 0.5–200 mJ (at a storage voltage from 4 to 15 kV and the discharge current range of 6–26 kA, respectively). The discharge gap images were obtained using a pinhole camera in the EUV and soft X-ray ranges of 15–73 eV and 80–284 eV energy. It is shown that micropinch formation in the plasma cathode jet occurs, mainly, in the matter evaporated by the laser pulse at the discharge ignition near the moment when the current derivative reaches the maximum. It is found that the cathode jet may consist of several pinched areas, and each of them has its own structure, and the improvement of the discharge and laser radiation parameters allows us to reach a stable single pinching of plasma. The parameters of the micropinch (the plasma compression ratio, size, and position of the emitting area in the interelectrode gap) as well as the current flow through the interelectrode gap, at the given storage voltage, are completely governed by the laser radiation characteristics.
The formation of a current-plasma shell is studied during the expansion of a laser-ignited low-power vacuum-discharge cathode plasma jet into the interelectrode gap. The shell geometry is found to be determined by the mode of laser-plasma expansion at the discharge ignition stage. It is shown that the increase in the laser-beam focal spot area on the cathode surface leads to the increase in the matter density and the decrease in the density gradient in the discharge gap and to transition from the spherical laser-plasma expansion mode to the jet mode. The latter considerably stabilizes the current transfer in the discharge plasma, even during the development of the hydrodynamic sausage instability in it.
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