  A new target design is presented to model high-energy radiative accretion
shocks in polars. In this paper, we present the experimental results obtained
on the GEKKO XII laser facility for the POLAR project. The experimental results
are compared with 2D FCI2 simulations to characterize the dynamics and the
structure of plasma flow before and after the collision. The good agreement
between simulations and experimental data confirm the formation of a reverse
shock where cooling losses start modifying the post-shock region. With the
multi-material structure of the target, a hydrodynamic collimation is exhibited
and a radiative structure coupled with the reverse shock is highlighted in both
experimental data and simulations. The flexibility on the laser energy produced
on GEKKO XII, allowed us to produce high-velocity flows and study new and
interesting radiation hydrodynamic regimes between those obtained on the
LULI2000 and Orion laser facilities.
