A model for degradation of indirectly driven ICF implosions by supra-thermal electron preheat

In recent years, significant progress has been made in the performance of indirectly driven inertial confinement fusion (ICF) implosions performed on the National Ignition Facility (NIF). Experimental results to date, however, have fallen short of the predicted neutron yield, the expected compression of the deuterium-tritium (DT) fuel layer, and the pressure and density achieved in the central hot spot. A numerical model is presented for the degradation of implosion performance due to preheat of the DT fuel layer by supra-thermal electrons. The model is benchmarked by comparison with focused experiments, which directly measure the expansion of a DT ice layer caused by preheat from a controlled, well-characterized flux of supra-thermal electrons. The same model applied to ignition implosions shows improved agreement with a wide range of experimental observables, and may help to provide an explanation for many of the features observed in ignition implosions on the NIF.