Spectroscopic measurements on vacuum spark plasmas

Abstract

Photoelectric spectra of the regions corresponding to resonance line emission of He-like ions of titanium, iron, and copper from a low-inductance vacuum spark were obtained, as were spectra of the regions corresponding to $K\ensuremath{\alpha}$ and $K\ensuremath{\beta}$ emission from the same elements and to $K\ensuremath{\beta}$ emission of molybdenum. Electron temperatures are estimated from continuous x-ray emission spectra to $\ensuremath{\kappa}{T}_{e}\ensuremath{\lesssim}15$ keV; ion temperatures from x-ray line widths to $\ensuremath{\kappa}{T}_{i}\ensuremath{\lesssim}10$ keV. A broad peak superimposed on the visible continuum is interpreted as anomalous bremsstrahlung at twice the electron plasma frequency. The resultant electron density is ${N}_{e}\ensuremath{\approx}5\ifmmode\times\else\texttimes\fi{}{10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, consistent with the absence of forbidden He-like ion lines. Experimental observations support the suggestion that the x-ray-producing dense plasmas are due to interactions between pulsed electron beams and low-temperature anode vapors or plasmas.