Properties of the ''pre-pinched'' phase of vacuum spark plasmas ofintermediate (Z∼20--30) and high (Z∼60) atoms

Space resolved-vacuum spark spectra of titanium, vanadium, iron, nickel, copper, gallium and rare earths, cerium and samarium, have been recorded in the 7 to 27 A range. Line ratios of NeI-like charge states in the intermediate Z cases and NiI-like for the high Z atoms have been used to estimate the electron temperature and density of the emitting plasmas. In general, it has been found that the above mentioned ions emitted from plasmas having dimensions of the order of several hundreds of microns; the densities were in the range 1019 to 1021 cm-3 and the temperatures, 200 to 500 eV. These parameters indicate that the L and M-shell emission is originating from a phase preceding the final collapse of the plasma to a very dense-high temperature micro-pinch, the ''pre-pinch'', in accordance with the radiative collapse model. The possible optimization of the ''pre-pinch'' plasma as a soft x-ray source for lithography or microscopy is briefly discussed