Thermonuclear Ignition and the Onset of Propagating Burn in Inertial Fusion

Defining ignition in inertial confinement fusion (ICF) is an unresolved problem. In ICF, a distinction must be made between the ignition of the hot spot and the propagation of the burn wave in the surrounding dense fuel since most of the energy gain comes from burning the dense shell. In this work, we used a large 1-D simulation ensemble to show that it is possible to identify the onset of ignition through a unique value of the yield amplification defined as the ratio of the fusion yield including alpha-particle deposition to the fusion yield without alphas. Since the yield amplification is a function of the fractional alpha energy (total alpha energy/hot-spot energy, a measurable quantity), it appears possible not only to define ignition but also to measure the onset of ignition by the experimental inference of the fractional alpha energy and yield amplification. We also investigate the impacts of low- and mid-mode asymmetries on this ignition curve and how the definition of ignition is modified by these perturbations.