OMEGA Experiments of Dynamic Shell Formation for Inertial Confinement Fusion*

This talk reports on the novel concept of the dynamic-shell (DS) formation [Goncharov et al., Phys. Rev. Lett. 125, 065001 (2020)] and its demonstration in a proof-of-principle experiment on the OMEGA laser using a scaled-down surrogate version of the target. The DS concept holds great promise for future applications in inertial fusion energy and it uses a spherical target that is initially in the form of a homogeneous deuterium-tritium liquid inside a wetted-foam spherical shell. The target is irradiated directly by laser beams in a series of laser pulses that initially compress the fuel that is then followed by an expansion. The expansion of the fuel cloud is then the slowed down and reversed by a sequence of intense laser pulses that eventually lead to the dynamic formation of a high-density DT fuel shell with a low-density interior. This shell target is then imploded and ignited like in the conventional laser-driven inertial confinement fusion hot-spot scheme. For the first time, the feasibility of the DS formation has been experimentally demonstrated on OMEGA using a scaled down version of the target with an ambient surrogate foam-sphere target. The design had to satisfy the limitations of the OMEGA laser in available energy and pulse duration. A shell was formed by series of convergent shock waves that were launched by laser pulses at the edge of the plasma sphere, with the plasma itself formed because of laser-driven compression and relaxation of the plastic-foam ball target. Three x-ray diagnostics, including 1-D spatially resolved self-emission-streaked imaging, 2-D self-emission framed imaging, and backlighting radiography, have shown good agreement with synthetic x-ray radiographs that were obtained by postprocessing the results of radiation-hydrodynamic simulations. The results enable us to verify the predicted evolution of the DS and its stability to low Legendre mode perturbations introduced by laser irradiation and target asymmetries.