Electron density measurement of a pre-pinched vacuum spark plasma using soft X-ray titanium and vanadium emission

Abstract

Spectra of elements belonging to the iron group, emitted from a low inductance, high voltage vacuum spark, have been recorded in the 10-20 AA range by means of a slitless RbAP crystal spectrometer. From the space- and energy-resolved spectra the authors conclude that the Ne I-like ions emit their line radiation from a relatively extended plasma region, the 'pre-pinch'. In similar discharges, titanium spectra have been recorded in the 10-100 AA range by a 2 m grazing incidence Schwob-Fraenkel spectrometer. The experimental intensities of the Ti XIII, Ne I-like 2p6-2p53l (l=s, d) and 2s2p6-2s2p63p El transitions have been compared with intensities predicted by a non-LTE collisional-radiative atomic model of the Ne I-like emission. The model includes the effect of recombination from F I-like ions and inner-shell ionisation of Na I-like ions, in addition to electron impact and radiative transitions. Based on the spatially imaged results and the comparison of experimental and theoretical line intensities, the authors estimate an electron density of approximately 6*1019 cm-3 in the pre-pinch phase of the vacuum spark plasma. The estimated electron temperature of the emitting plasma is 200-300 eV and its spatial extent is determined to be of the order of 200 mu m.