Burn regimes in the hydrodynamic scaling of perturbed inertial confinement fusion hotspots

Abstract

We present simulations of ignition and burn based on the Highfoot and\nHigh-Density Carbon indirect drive designs of the National Ignition Facility\nfor three regimes of alpha-heating - self-heating, robust ignition and\npropagating burn - exploring hotspot power balance, perturbations and\nhydrodynamic scaling. A Monte-Carlo Particle-in-Cell charged particle transport\npackage for the radiation-magnetohydrodynamics code Chimera was developed for\nthis work. Hotspot power balance between alpha-heating, electron thermal\nconduction and radiation was studied in 1D for each regime, and the impact of\nperturbations on this power balance explored in 3D using a single\nRayleigh-Taylor spike. Heat flow into the spike from thermal conduction and\nalpha-heating increases by $\\sim2-3\\times$, due to sharper temperature\ngradients and increased proximity of the cold, dense material to the main\nfusion regions respectively. The radiative contribution remains largely\nunaffected in magnitude. Hydrodynamic scaling with capsule size and laser\nenergy of two perturbation scenarios (a short-wavelength multi-mode & a\nlow-mode radiation asymmetry) is explored in 3D, demonstrating the differing\nhydrodynamic evolution of the three alpha-heating regimes. The multi-mode yield\nincreases faster with scale factor due to more synchronous $PdV$ compression\nproducing higher temperatures and densities, and hence stronger bootstrapping.\nEffects on the hydrodynamic evolution are clearer for stronger alpha-heating\nregimes and include: reduced perturbation growth due to ablation from\nfire-polishing and stronger thermal conduction; sharper temperature and density\ngradients; and increased hotspot pressures which further compress the shell,\nincrease hotspot size and induce faster re-expansion. Faster expansion into\nregions of weak confinement is more prominent for stronger alpha-heating\nregimes, and can result in loss of confinement.\n