Spectroscopic measurements on vacuum spark plasmas

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 $K\alpha$ and $K\beta$ emission from the same elements and to $K\beta$ emission of molybdenum. Electron temperatures are estimated from continuous x-ray emission spectra to $\kappa T_e\lesssim 15$ keV; ion temperatures from x-ray line widths to $\kappa T_i\lesssim 10$ 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 $N_e\approx 5\times {10}^{20}$ ${\mathrm{cm}}^{-3\mathrm{}}$, 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.