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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Studies of x-ray emission from a laser induced vacuum discharge of moderate storage energy (<20 J) are examined. It is found that micropinches in the initial stage of the cathode jet expansion into the interelectrode gap are formed. Hot plasma of the micropinches emits a soft x-ray radiation and beams of accelerated electrons moving toward the anode. It is found that these phenomena occur just when both amplitude of the discharge current and energy of the initiating laser pulse lie in the specified ranges of values. The position of the micropinch within the interelectrode gap and also the intensity of the x-ray radiation and beams of the accelerated electrons emitted from the micropinch are variable over a wide range of values through changes in energy of the laser pulse and/or amplitude of the discharge current. The experimental results are compared with the data of the particle-in-cell simulations and a fair agreement is found between them.

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A comparative study of the characteristics of moderate-current (∼10kA), low-energy (⩽20J) vacuum discharge triggered by multipicosecond and nanosecond duration laser pulses is performed. Temporal profiles of the x-ray emission, discharge current, and anode voltage measured in vacuum discharge created between a planar titanium cathode and a conical point-tip anode are observed to be quite different for the two regimes of the laser pulse duration. While cathode plasma jet pinching is clearly observed in the discharge created by low-energy (∼5mJ), 27 ps full width at half-maximum (FWHM) laser pulses, a feeble pinching occurred for 4 ns (FWHM) laser pulses only above a threshold energy of ∼250mJ. In addition to the multiple K-shell x-ray pulses emitted from the titanium anode up to 100 ns, evidence of a much harder x-ray component (hν&gt;100keV) is also seen in the discharge triggered by picosecond laser pulses.

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