SPECTROSCOPIC DIAGNOSTICS IN A COLLIDING-BLAST-WAVE EXPERIMENT

Visible spectral lines from n = 3, DELTAn = 0 transitions in N+ and N2+ ions are used for measuring the plasma electron density and temperature in a region of two colliding blast waves, propagating through a 1.5-10-Torr nitrogen atmosphere. The blast waves originate at the tips of two aluminum rods irradiated with two beams of the Naval Research Laboratory (NRL) Pharos-III 1.054-mum-wavelength Nd:glass laser operated at an energy of 200-430 J for each beam in 5-ns pulses. An electron density in the colliding-blast-wave region of N(e) almost-equal-to 10(18) cm-3 was deduced from Stark broadening of spectral lines from N+ ions. An electron temperature of T(e) almost-equal-to 4 eV was measured in this region from a spectral-line intensity ratio between N2+ and N+ ions. Near one target, an electron density of N(e) almost-equal-to 8 X 10(20) cm-3 was determined from series-limit x-ray spectral-line merging; a mean electron temperature of kT(e) almost-equal-to 225 eV was determined from x-ray fine-intensity ratios. Some evidence was found for enhanced velocities for blast waves propagating through a plasma formed by a preceding blast wave.