Particle-in-Cell Simulations of Burning ICF Capsule Implosions

TL;DR

This paper introduces a particle-in-cell simulation code to study the burn stage in inertial confinement fusion, revealing the role of suprathermal ions and analyzing neutron signals in NIF experiments.

Contribution

Development of the PICNIC particle-in-cell code for simulating ICF burn stages, incorporating energy conservation and collision physics, to interpret neutron signals and plasma behavior.

Findings

Suprathermal ions produce neutron signals consistent with experiments.

Large-angle scattering does not account for observed spectral shifts.

Simulation results help understand kinetic effects in ICF plasmas.

Abstract

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 offer a direct probe of the stopping power in the burning fuel region of high energy alpha particles and up-scattered fuel ions. We have developed the particle-in-cell code PICNIC, an exactly energy-conserving particle-in-cell Monte-Carlo collision (PIC-MCC) code to simulate the burn stage in ICF. We present results from 1D spherical simulations of NIF shot N210808. We find that the suprathermal ions generated by large-angle Rutherford and nuclear elastic scattering (NES) with fusion alphas produce an alpha knock-on neutron (AKN) signal consistent with experiments. We also find that the inclusion of large-angle scattering physics does not explain the anomalously large spectral shift observed in experiment.