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

## TL;DR

This study uses advanced simulations to analyze different burn regimes in inertial confinement fusion, revealing how perturbations and scaling affect hotspot stability, power balance, and overall fusion performance.

## Contribution

It introduces a Monte-Carlo Particle-in-Cell charged particle transport package for Chimera and explores hydrodynamic scaling across three alpha-heating regimes in detail.

## Key findings

- Heat flow into perturbations increases by 2-3 times with sharper temperature gradients.
- Hydrodynamic scaling shows faster yield increase with scale for multi-mode perturbations.
- Stronger alpha-heating regimes exhibit reduced perturbation growth and sharper gradients.

## Abstract

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