Excitation temperature, degree of ionization of added iron species, and electron density in an exploding thin film plasma

Abstract

Time and spacially resolved spectra of a cylindrically symmetric exploding thin film plasma were obtained with a rotating mirror camera and astigmatic imaging. These spectra were decouvolved to obtain relative spectral emissivity profiles for nine Fe(II) and two Fe(I) lines. The effective (electronic) excitation temperature at various positions in the plasma and at various times during the first current halfcycle was computed from the Fe(II) emissivity values using the Boltzmann graphical method. The Fe(II)/Fe(I) emissivity ratios together with the temperature were used to determine the degree of ionization of Fe. Finally, the electron density was estimated from the Saha equilibrium. Electronic excitation temperatures range from 10,000-15,000 K near the electrode surface at peak discharge current to 7000-10,000 K at 6-10 mm above the electrode surface at the first current zero. Corresponding electron densities range from 1017-1018 cm-3 at peak current to 1015-1016cm-3 near zero current. Error propagation and criteria for thermodynamic equilibrium are discussed.