Particle-in-Cell Simulations of Burning Capsule Implosions

Anomalies observed in the neutron spectral shift of high-yield shots at the National Ignition Facility (NIF) suggest the presence of suprathermal ions, implying that kinetic effects play a significant role in burning Inertial Confinement Fusion (ICF) plasmas. Furthermore, recent measurements of reaction-in-flight (RIF) neutrons, and specifically alpha knock-on neutrons (AKN), can provide a direct probe of the stopping power in the burning fuel region of high-energy alpha and up-scattered D/T ions. We therefore aim to provide a tool capable of performing fully kinetic simulations of the complete capsule in burning implosions.



We have developed the radiation-particle-in-cell code PICNIC, an exactly energy-conserving, electromagnetic and fully relativistic particle-in-cell Monte-Carlo Collision (PIC-MCC) code capable of simulating the full burn stage in ICF. Collisions are handled with a moment-preserving binary-pair MCC algorithm for moderately coupled plasmas. The algorithm includes both cumulative small-angle Coulomb and single large-angle Rutherford scattering, as well as alpha-D/T nuclear elastic scattering to accurately model the alpha up-scattering of D/T fuel ions to multi-MeV energies in the burnwave. We present results of 1D spherical simulations of NIF shot N210808-001, with initial conditions provided by HYDRA. We find that the suprathermal ions generated by large-angle collisions with fusion alphas produce an AKN signal consistent with experiments. However, we also find that large-angle collisions do not explain the large measured spectral shift.