Investigating the Differences Between Implosion Convergence Inferred From X-Ray Images and Secondary DT Neutrons At The NIF

An important figure of merit for the performance of an ICF (Inertial Confinement Fusion) implosion is the capsule convergence: the ratio of the initial and final capsule radii.  On the NIF, this is routinely inferred using imaging of the capsule’s self-emitted x-rays during peak compression. Additionally though, the yield ratio of secondary DT neutrons to primary DD neutrons can also be used to infer capsule convergence in deuterium-filled capsules. While these independent inferences track one another, x-ray imaging generally implies higher convergences (smaller final radii) than the secondary neutron based analysis. Understanding the nature of these differences could potentially offer interesting insights on the sensitivities of both methods to effects like high-Z mix, asymmetries, analysis assumptions, and plasma profiles. This work is supported in part by the U.S. Department of Energy and Lawrence Livermore National Laboratory.