Study of Direct-Drive-targets stability by varying pulse shapes, filling pressure and ablator thickness on the OMEGA laser facility

In the context of imploding capsules studies, X-ray heating from laser irradiated hohlraum produces implosions showing that the understanding via simulations of the hydrodynamics (bang times) and performances ( neutron yields) are difficult because the discrepancies with experimental results are important. In the experiments presented here, we studied targets stability in the Direct-Drive heating scheme by varying pulse shapes, filling pressure, ablator thickness and laser energy (non-uniform irradiation). The main objectives have been to get bang-times and neutron yields measurements, neutron images of the imploding core on the OMEGA laser facility. X-ray images have been obtained for the first time on the same axis and lead to direct comparison of the size and location of the X-ray and neutron hot spots. Precise measurements of bang times, X-ray spectra and soft X-ray images from temporally gated imaging systems give large set of data to validate simulations and assess how predictable are the different experimental configurations of implosion.