NIF achieves symmetric capsule implosion

Researchers have begun using the 192 laser beams of the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL; Livermore, CA) to implode spherical fusion capsules. These capsules will eventually contain small amounts of deuterium and tritium that will act as the ignition source for sustained fusion. In preparation for that goal (experiments with deuterium/tritium fuel will begin in summer 2010), the researchers must first demonstrate that implosions are symmetrical in nature, meaning that the energy on the capsule's surface is optimized for fusion burn.

After several attempts over the last few months that produced elliptical implosion signatures, the NIF scientists announced that they had just symmetrically imploded 1.8 mm helium/deuterium-filled capsules at 20 Kelvin (K) that demonstrated efficient hohlraum heating to radiation temperatures of 3.3 million K. The x-ray emission images at 9 keV at a peak emission time of 18 ± 0.15 ns show shape changes from elliptical to circular based on varying the laser-wavelength difference for beams that strike the radiation enclosure (hohlraum) closer to the axis of its cylinder (the inner beams) and further from its axis (the outer beams). A nominal separation of 1.7 Å yields the most symmetrical result. Contact Siegfried H. Glenzer at glenzer1@llnl.gov.

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