Experimental Signatures of Burn Propagation and Robust Ignition in Laser Indirect Drive Implosions on the National Ignition Facility

An important aspect of central hot-spot ignition implosion designs is observing that the central ignited hot-spot is able to propagate the fusion burn into the surrounding cold fuel. The only diagnostic that can measure the dynamics of thermonuclear burn is the nuclear fusion reaction history as a function of time. Distinct signatures in the α-curve of the reaction history have been found to be metrics of burn propagation, as well as robust ignition where the fuel mass is able to heat itself and the ice layer faster than the expansion rate decreases fusion rate. Recent advances in the Gamma Reaction History diagnostic (GRH) at the NIF have enabled measurements of the reaction history with 7 ps temporal resolution which is adequate to capture the signatures of burn propagation in the NIF. Measurements of the α-curve of ignited NIF experiments have shown signatures consistent with an ablative burn propagation model and are in agreement with xRAGE simulations. Recent high-gain implosions have shown the signatures of robust ignition predicted by analytic theory and simulations.