  Refraction-enhanced x-ray radiography (REXR) is used to infer shock-wave
positions of more than one shock wave, launched by a multiple-picket pulse in a
planar plastic foil. This includes locating shock waves before the shocks
merge, during the early time and the main drive of the laser pulse that is not
possible with the velocity interferometer system for any reflector. Simulations
presented in this paper of REXR show that it is necessary to incorporate
refraction and attenuation of x rays along with the appropriate opacity and
refractive-index tables to interpret experimental images. Simulated REXR shows
good agreement with an experiment done on the OMEGA laser facility to image a
shock wave. REXR can be applied to design multiple-picket pulses with a better
understanding of the shock locations. This will be beneficial to obtain the
required adiabats for inertial confinement fusion implosions.
