Decreasing Necessary Optimization Time For Increases In Neutron Yieldof Direct-Drive Inertial Confinement Fusion ImplosionsUsing a Three-Dimensional Contoured Fuel Shell*

In the pursuit of achieving energy output exceeding input in direct-drive inertial

confinement fusion, ensuring uniform fuel compression in the final implosion

stages presents a significant challenge. In experimental setups, energy is delivered using a

finite number of beams spaced in a spherical geometry (e.g., 60 beams for OMEGA 1 ) and

results in uneven laser-energy deposition, with some regions becoming hotter than

others. Consequently, the compression becomes aspherical, leading to a

perturbed implosion during the critical stage of maximum fusion reactions (i.e., “bang

time”;). By employing the 3-D code ASTER2, our objective in

this simulation is to enhance the neutron yield by adjusting the thickness of the target

shell in three dimensions, in order to account for the spherical asymmetry present at bang

time. To assess the effectiveness of this approach, we calculate the sphericity of the target

at various time points, including bang time. As the sphericity approaches unity, it should

correlate with increasing neutron yields.  This is even true for time points preceding bang

-time, therefore eliminating the need to simulate implosions until bang time and

also saving valuable optimization time.