Core conditions for alpha heating attained in direct-drive inertial confinement fusion

It is shown that direct-drive implosions on the OMEGA laser have achieved core conditions that would lead to significant alpha heating at incident energies available on the National Ignition Facility (NIF) scale. The extrapolation of the experimental results from OMEGA to NIF energy assumes only that the implosion hydrodynamic efficiency is unchanged at higher energies. This approach is independent of the uncertainties in the physical mechanism that degrade implosions on OMEGA, and relies solely on a volumetric scaling of the experimentally observed core conditions. It is estimated that the current best-performing OMEGA implosion [Regan et al., Phys. Rev. Lett. 117, 025001 (2016)] extrapolated to a 1.9 MJ laser driver with the same illumination configuration and laser-target coupling would produce 125 kJ of fusion energy with similar levels of alpha heating observed in current highest performing indirect-drive NIF implosions.

Figure 1

OMEGA cryogenic implosion 77068: (a) laser power versus time (b) and target design.

Figure 2

Density contour plots from dec2d at time of peak neutron rate for OMEGA shot 77068 (a) and hydroequivalent 1.9 MJ direct-drive implosion with alpha-particle energy deposition (b).

Figure 3

Time integrated x-ray images of the hot spot from (a) experiment and (b) reconstructed from simulation; (c) comparison of intensity profiles along dashed line.