The National Nuclear Security Administration (NNSA) and Lawrence Livermore National Laboratory (LLNL) today announced that the National Ignition Facility (NIF) recently completed its first integrated ignition experiment. In the test, the 192-beam laser system fired 1 megajoule of laser energy into its first cryogenically layered capsule, raising the drive energy by a factor of thirty over experiments previously conducted at the Omega laser at the University of Rochester. With the completion of this test, NIF is beginning its next phase of the campaign to culminate in fusion ignition tests.
The experiment demonstrated the integration of the complex systems required for an ignition campaign. This target was filled with a mixture of tritium, hydrogen and deuterium tailored to enable the most comprehensive physics, a necessary step on the path to demonstrating fusion ignition. All systems operated successfully, and 26 target diagnostics participated in the shot.
They used a frozen capsule -- chilled to minus 425 Fahrenheit -- contained two hydrogen variants, deuterium and tritium, as well as plain hydrogen. It yielded approximately 1,000 times more neutrons than earlier experiments at NIF with gaseous forms of deuterium and tritium. Neutrons are the energy source that will drive fusion ignition reactions.
Scientists at NIF have experimented with gaseous forms of deuterium and tritium, but using a frozen fuel pellet in fusion ignition experiments is essential. The fuel pellet ultimately needs to be 100 times more dense than lead for fusion ignition, Moses explained. "So if you start with the frozen form, it gets you 10 times the way there," Moses said.
Since the fuel mixture included hydrogen, scientists didn't expect the experiment to yield a fusion reaction, because hydrogen "sort of keeps it cool," Moses said. "And keeping it cool prevents it from going to burn." NIF scientists wanted to hold off on attempting fusion "burn," or ignition, with the Sept. 29 experiment.
Future experiments will use only deuterium and tritium in attempts to achieve actual fusion, but the deuterium-hydrogen-tritium combination allows scientists to calibrate the system, as well as test 26 new diagnostic instruments that measure the results. Scientists at NIF hope to achieve fusion by 2012, Moses said.
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