Effects of asymmetry and hot spot shape on ignition

Asymmetric implosion of inertial confinement fusion capsules is known, both experimentally and computationally, to reduce thermonuclear (TN) performance. This work shows that low-mode asymmetries degrade performance as a result of decrease in the hydrodynamic disassembly time of the hot spot core, which scales with the minimum dimension of the hot spot. The asymmetric shape of a hot spot results in decreased temperatures and areal densities and allows more alpha particles to escape, relative to an ideal spherical implosion, thus reducing alpha-energy deposition in the hot spot. Here, we extend previous ignition theory to include the hot-spot shape and quantify the effects of asymmetry on both the ignition criterion and capsule performance. The ignition criterion becomes more stringent with increasing deformation of the hot spot. The new results are validated by comparison with NIF experimental data. The shape effects on TN performance become more noticeable as both self-heating and yield increase. The degradation of TN burn can be as high as 45% for shots with yield lower than 2x10¹⁵and less than 30% for shots with yield above. 

This work was performed under the auspices of the U.S. Department of Energy by the Los Alamos National Laboratory under Contract No. W-7405-ENG-36.