Thermal radiation from a converging shock implosion

Authors: Kjellander, M. K., Tillmark, N.T., Apazidis, N.
Document Type: Article
Pubstate: Published
Journal: Physics of Fluids
Volume: 22   046102
Year: 2010


High energy concentration in gas is produced experimentally by focusing cylindrical shock waves in a specially constructed shock tube. The energy concentration is manifested by the formation of a hot gas core emitting light at the center of a test chamber at the instant of shock focus. Experimental and numerical investigations show that the shape of the shock wave close to the center of convergence has a large influence on the energy concentration level. Circular shocks are unstable and the resulting light emission varies greatly from run to run. Symmetry and stability of the converging shock are achieved by wing-shaped flow dividers mounted radially in the test chamber, forming the shock into a more stable polygonal shape. Photometric an spectroscopic analysis of the implosion light flash from a polygonal shock wave in argon is performed. A series of 60 ns time-resolved spectra spread over the 8 $\mu$s light flash show the emission variation over the flash duration. Blackbody fits of the spectroscopic data give a maximum measured gas temperature of $5800$ K in the beginning of the light flash. Line emissions originating in transitions in neutral argon atoms from energy levels of up to 14.7 eV were also detected.