Nourou Amadou

Laser-driven quasi-isentropic compression experiments and numerical studies of the iron alpha-epsilon transition in the context of planetology

The iron alpha-epsilon transition is one of the most studied solid-solid phase transition. However, for quasi-isentropic compression, the dynamic and the influences of this transition on the high-pressure states of iron are still unknown. We present experimental results and numerical simulations to study these effects. Experiments performed at LULI2000 and the Janus laser facility (LNLL), using two different ramp shapes and different compression rates allowed to study the dynamic of the alpha-epsilon transition. We have observed the transition at particle velocity ranging from 0.25 km/s to 0.52 km/s depending on the compression rate. Depending on the ramp, either a shock formation was observed (high compression rate) at the transition or a flat plateau whose duration is function of compression rate. Increasing the compression rate leads to a smaller plateau duration. These results are important for reproducing Earth and Super-earth core conditions (2-15Mbar, 5- 15000K) on laboratory where the quasi-isentropic compression is the most promising experimental scheme.

Characterization of laser-driven ultrafast shockless compression using gold targets

Indirect laser-driven shockless compression experiments on gold targets were performed to characterize pressure loading processes and target states. Free surface velocities of the gold target under ramped pressure loading were measured using line-imaging velocity interferometers. From the velocity data and the equation of state, the maximum pressure and strain rate attained under compression were estimated to be ∼50 GPa and ∼4 × 107 s−1, respectively. Optical reflectivity was measured simultaneously with the velocity, the result suggesting no significant or unexpected temperature increases in the ultrafast shockless compression process.