Indirect-drive hohlraum experiments at the National Ignition Facility have demonstrated symmetric capsule implosions at unprecedented laser drive energies of 0.7 MJ. 192 simultaneously fired laser beams heat ignition emulate hohlraums to radiation temperatures of 3.3 million Kelvin compressing 1.8-millimeter capsules by the soft x rays produced by the hohlraum. Self-generated plasma-optics gratings on either end of the hohlraum tune the laser power distribution in the hohlraum producing symmetric x-ray drive as inferred from the shape of the capsule self-emission. These experiments indicate conditions suitable for compressing deuterium-tritium filled capsules with the goal to achieve burning fusion plasmas and energy gain in the laboratory.With completion (1) and commissioning (2) of the National Ignition Facility (NIF) the quest for producing a burning fusion plasma has begun (3, 4). The goal of these experiments is to compress matter to densities and temperatures higher than the interior of the sun (5-7) which will initiate nuclear fusion and burn of hydrogen isotopes (8-10). This technique holds promise to demonstrate a highly efficient carbon-free process that will burn milligram quantities of nuclear fuel on each laser shot for producing energy gain in the laboratory.The NIF (11) consists of 192 laser beams that have been arranged into cones of beams to irradiate a target from the top and bottom hemispheres. This "indirect-drive" laser geometry has been chosen for the first experiments to heat the interior of centimeter-scale cylindrical gold hohlraums (8,(12)(13)(14)(15) through laser entrance holes (LEH) on the top and bottom end of the cylinder (Fig. 1). Hohlraums act as radiation enclosures that convert the optical laser light into soft x-rays that are characterized by the radiation temperature T RAD . Present ignition designs operate at temperatures of 270 to 305 eV or 3.1 to 3.5 million K. The radiation field compresses a spherical fusion capsule mounted in the center of the hohlraum by x-ray ablation of the outer shell. The ablation process compresses the cryogenically prepared solid deuterium-tritium fuel layer in a spherical rocket implosion. In the final stages, the fuel reaches densities 1000-times solid and the central hot spot temperatures will approach 100 million K to initiate the nuclear burn process.We have symmetrically imploded 1.8-mm diameter fusion capsules in cryogenically fielded centimeter-scale hohlraums at 20 K. These experiments show efficient hohlraum heating to radiation temperatures of 3.3 million K. In addition, the large scale-length plasmas encountered in these experiments have allowed us to use self-generated plasma optics gratings (16) to control the radiation symmetry (17) and to achieve symmetric fusion capsule implosions.Figure 2 A shows the laser power at the frequency-tripled wavelength of 351 nm versus time for two different pulse shapes. These 11-ns and 16-ns long pulses heat 8.4-mm long, 4.6-mm diameter hohlraums with 20% helium, 80% hydrogen (atomic) mixtures and ...

A line-imaging velocity interferometer has been implemented at the OMEGA laser facility of the Laboratory for Laser Energetics, University of Rochester. This instrument is the primary diagnostic for a variety of experiments involving laser-driven shock wave propagation, including high pressure equation of state experiments, materials characterization experiments, shock characterization for Rayleigh-Taylor experiments, and shock timing experiments for inertial confinement fusion research. Using a laser probe beam to illuminate a target the instrument measures shock breakout times and Doppler shifts in the reflected light. Velocities of interfaces, free surfaces and of shock fronts traveling through transparent media can be measured for velocities ranging from 0.1 to greater than 50 km/s with accuracies ∼ 1% over most of this range. Quantitative measurements of the optical reflectance of ionizing shock fronts can also be obtained simultaneous with the velocity measurements.

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The Hohlraum energetics experimental campaign started in the summer of 2009 on the National Ignition Facility (NIF) [E. I. Moses et al., Phys. Plasmas 16, 041006 (2009)]. These experiments showed good coupling of the laser energy into the targets [N. Meezan et al., Phys. Plasmas 17, 056304 (2010)]. They have also demonstrated controlled crossed-beam energy transfer between laser beams as an efficient and robust tool to tune the implosion symmetry of ignition capsules, as predicted by earlier calculations [P. Michel et al., Phys. Rev. Lett. 102, 025004 (2009)]. A new linear model calculating crossed-beam energy transfer between cones of beams on the NIF has been developed. The model has been applied to the subscale Hohlraum targets shot during the National Ignition Campaign in 2009. A good agreement can be found between the calculations and the experiments when the impaired propagation of the laser beams due to backscatter is accounted for.