An experimental study of the hydrodynamics of reduced density channels

The formation and decay of reduced density channels in gaseous atmospheres was studied using a novel method to produce channels in nitrogen by the absorption of pulsed carbon dioxide laser radiation. These experiments were performed in a chamber consisting of three regions: a nonabsorbing convergence section filled with pure nitrogen in which the CO2 laser beam was focused to small diameter and high intensity; a windowless transition region; and an absorption section filled with nitrogen containing a small percentage of SF6. The amount of laser energy absorbed in the gas (about or greater than 0.4 J/cc) and the radius of the laser beam (about 2mm) were measured throughout the absorption section. The radial density profile of the resulting channel was determined as a function of time by several optical methods. Hydrocode simulations of the evolution of the radial density profile of the channel were performed based on the measured initial conditions and agree with the measured results for the first about 100 microseconds of the life of the channel.