Measurements of Improved Hohlraum Efficiency for Near Term Burning Plasma Designs

Experiments conducted on the NIF using a 420 TW, 1.7 MJ Hybrid E design (see A. Zylstra invited) 3-rise laser pulse and a pure gold hohlraum have demonstrated an increase in radiation temperature by 20 eV from 292 to 312 eV. The experimental results show the systematic increase in radiation temperature with decreasing diameter of the laser entrance hole from 3.64 mm to 3.1 mm. A 1.1 mm inner radius high density carbon ablator filled with deuterium and Helium-3 was used to assess the performance gains and impact on implosion symmetry. Results show the higher radiation temperatures led to increases in velocity measured through in-flight radiography and peak x-ray core emission time, a doubling of the DD fusion yield and a 15% increase in hot spot temperature. These increases in hohlraum efficiency were obtained while maintaining P2 symmetry within 7 microns of round. Results from hydrodynamic simulations will be shown and compared to experimental results. Simulations, closely matching the experimental results indicate these improvements could increase energy to the capsule in a hybrid E like design from 214 presently to as high as 330±20 kJ. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.