
FIRST STEPS TOWARD FUSION AT NIF
Date: Wednesday, November 23, 2005 @ 20:18:34 UTC Topic: Science
From The American Institute of Physics Bulletin of Physics News Number 755
November 23, 2005 by Phillip F. Schewe, Ben Stein, and Davide
Castelvecchi:
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 initial density) 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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