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Axially inhomogeneous plasma in fast discharges for creation of population inversion in soft x-ray region

Self-organizing 'neck' type instabilities in capillary discharges are believed to be responsible for the population inversion in vacuum ultraviolet (VUV) spectral region. Selective population of the lasing levels originates as a result of charge–exchange recombination of the hot plasma ions during their flow from 'necks' into the cold surrounding gas. We propose a new approach of the 'induced neck' exploiting the axially inhomogeneous shock wave, generated in a capillary with a special wall profile and with high discharge current time derivative (about 1012 A s−1). A series of experiments with argon filling of the profiled capillary tube were performed. Time resolved pinhole VUV images of the discharge volume demonstrate the presence of the hot and compressed plasma objects on the discharge axes. All of them reproducibly appear at the same time and strictly on the axis of the capillary, in accordance with the wall structure. The VUV spectra, emitted by the compressed plasma, indicate a rather high electron temperature (50–100 eV), which must be sufficient for the production of hot plasma outflow.