FIRST STEPS TOWARD FUSION AT NIF
Laser pulses shot into a cavity can produce the conditions required to trigger nuclear fusion reactions, scientists at Lawrence Livermore National Laboratory in California report. The finding was a crucial test of principle for Livermore's National Ignition Facility (NIF,
http://www.llnl.gov/nif/project/index.html ), the $3.5 billion machine now under construction and expected to start full operations in 2009. NIF will produce fusion reactions by focusing 192 powerful ultraviolet laser beams through small holes into the hollow interior of a gold cavity called a hohlraum. The laser light quickly heats up the cavity's inner walls, which generate x rays, in a? few nanosecond-long bursts of energy more than 60 billion times as bright as the surface of the sun. The outer shell of a small capsule containing frozen deuterium and tritium placed inside this mini-oven will be heated by these x rays and rapidly expand, resulting in heating and compression of its core (to 1000 times its initialdensity) which will become as dense as the sun's center, triggering nuclear fusion.
During the first hohlraum experiments at NIF, a large team of physicists, engineers and technicians (contact: Eduard Dewald,
dewald3@llnl.gov, 925-422-7087) used the four existing NIF laser beams to prove NIF's x-ray production capability. NIF was operating at just 1 percent of its full design energy, and the cavity contained no fusion materials.? However, the x-ray flux inside the cavity---the amount of energy per unit area and per unit time---has been shown to agree with expectations, and is similar to those required for future fusion experiments. (Dewald et al., Physical Review Letters, 18 November 2005). Uncertainties over the continued funding of NIF seemed to be resolved in a recent House-Senate conference agreement over the 2006 energy bill (see FYI No. 162, November 11,
http://www.aip.org/fyi/2005/162.html ).
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