Performance tests of implosion velocity, coast, and adiabat using the Bigfoot platform on the National Ignition Facility (NIF)

For indirect drive inertial confinement fusion a spherical shell of DT fuel is imploded to reach the high density and temperature conditions needed for fusion. The Bigfoot approach uses a 3 shock laser pulse with a short foot, with the second shock overtaking the first in the ablator, to place the DT fuel on a high adiabat (~4). To understand the experimental tradeoffs between velocity and adiabat, the Bigfoot design was employed to study changes in velocity and adiabat in a series of experiments. These experiments varied the laser power and energy to test implosion performance with velocities from ~320 - 430 km/s and varied the length of the trough to access adiabats from 3 – 4. The impact of a 25% reduction in “coast” was also demonstrated. This set of experiments demonstrated low-mode symmetry control and performance that follows simple scalings for symmetry and performance. This high adiabat approach has led to the highest DT neutron yield achieved thus far on the NIF. The results of a scan in adiabat will also be presented. The results from this design are feeding into future designs for ignition on NIF.

*This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.