Fusion alpha particle momentum deposition in thermonuclear burn dynamics

TL;DR

This paper demonstrates that alpha particle momentum significantly impacts thermonuclear burn dynamics in inertial confinement fusion, reducing yield and affecting ignition conditions, thus requiring its inclusion in future models and designs.

Contribution

It introduces a Monte Carlo transport model to quantify alpha momentum effects, revealing their importance in current and scaled ignition regimes.

Findings

Alpha momentum reduces yield by ~30% at NIF scale.

Momentum deposition accelerates shell disassembly, affecting burn dynamics.

Persistent ~10% penalty in larger hydrodynamic scales.

Abstract

In inertial confinement fusion, the DT fusion alpha particles carry not only energy but also appreciable momentum that is typically neglected in models of thermonuclear burn. In the central hotspot ignition scheme, the hotspot must self-heat and propagate thermonuclear burn before disassembly. Using radiation hydrodynamics simulations with a Monte Carlo alpha particle transport model, we investigate the effect of alpha momentum deposition across sub-ignition to robustly igniting regimes by hydrodynamic scaling of current central hotspot ignition designs from the National Ignition Facility (NIF). We find that the effective alpha particle ram pressure accelerates the shell at burn, reducing hotspot compression, increasing the rate of disassembly and decreasing yield. This causes a notable (~ 30%) reduction in yield at current NIF scale, with a persistent (~ 10%) penalty at larger hydrodynamic scales. These results demonstrate that alpha momentum deposition is a significant effect for present ignition-scale implosions, necessitating its inclusion in ignition criteria, burn models, and designs for high-gain inertial confinement fusion.