Observations of the collapse of asymmetrically driven convergent shocks

The collapse of strong convergent shocks in spherical geometry is observed using measurements of induced nuclear production and x-ray emission. Precise and absolute measurements of the timing and yield of nuclear production induced by the collapse of laser-driven shocks give the same results when shocks are launched by uniform (<2% rms) or nonuniform (up to 32% rms) laser illumination. The observation was repeated for both low-mode (dominated by spherical harmonic modes l = 1-2) and high-mode (l = 31-500) drive asymmetries. For low-mode nonuniform drive, the center of collapse as observed through x-ray emission shifts away from target center toward the direction of low intensity. The x-ray emission brightness is seen to drop precipitously with larger low-mode drive asymmetry, in stark contrast to the drive-uniformity insensitivity of nuclear yields at the time of shock collapse. (C) 2008 American Institute of Physics.