Inertial fusion results from Nova and implication for the future of ICF

A key objective of the U.S. Inertial Confinement Fusion Program is to obtain high yield (100 to 1000 MJ) implosions in a laboratory environment. This requires high gain from an inertial fusion target from a driver capable of delivering about 10 MJ. Recent results have been sufficiently encouraging that the U.S. Department of Energy is planning for such a capability called the Laboratory Microfusion Facility (LMF). In the past two years, we have conducted implosion-related experiments with approximately 20 kJ of 0.35-micron laser light in 1-ns temporally flat-topped pulses. These experiments were done with the Nova laser, the primary U.S. facility devoted to radiatively driven inertial confinement fusion. Our results show that we can accurately model a significant fraction of the phenomena required to obtain the fuel conditions needed for high gain. Both the X-ray conversion efficiency and the growth of Rayleigh-Taylor hydrodynamic instabilities are shown to be at acceptable levels. Targets designed so that the shape of the stagnated fuel can be imaged show that the X-ray drive in our hohlraums can be made isotropic to better than 3 percent. With this optimized drive and temporally unshaped laser pulses many critical implosion parameters are measured on targets designed for higher density. Good agreement is obtained with one-dimensional simulations. Maximum compressions of between 20 to 30 in radius are measured with a variety of diagnostics. Improvements in the driver technology are demonstrated; we anticipate operation of Nova at the 50-kJ level at 3 microns.