Emission spectroscopic measurements and analysis of a pulsed plasma jet

An investigation has been conducted of the characteristics of a freely expanding pulsed plasma jet originating from an electrothermal capillary source. The evolution of the plasma jet was investigated using temporally-resolved emission imaging with a gated intensified CCD camera and temporally- and spatially-resolved emission spectroscopy. The emission images reveal a highly underexpanded plasma jet that forms a distinct barrel shock structure, with a highly luminous Mach disk. The jet structure reaches an approximately quasi-steady state about 70 ps after the initiation of the plasma. An analysis of the emission spectra along the jet axis indicates population temperatures in the expanded region, upstream of the Mach disk, to be 2.02 eV (23 400 K) and 1.4 eV (16 200 K), for time delays of 30 μs and 70 ps, respectively. At these same time delays, the electron number densities upstream of the Mach disk are of order 10¹⁷ cm^-3, but increase by an order of magnitude downstream of the Mach disk. Virtually no change is observed in the electron density across the Mach disk at a delay of 120 μs, indicating the shock front has largely dissipated