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Two proton spectrometers measured the spectra of
fusion protons leaving a NIF fuel capsule in different
directions for purposes of studying implosion symmetry
and areal density. Photo/LLE
A recent experiment at the OMEGA laser facility used fusion to study fusion. A laserdriven
ICF capsule (upper left) produced monoenergetic 3- and 15-MeV protons
through fusion reactions, and the protons were used to make radiographs of another
ICF capsule imploded by x-rays generated by the interaction of 30 laser beams with
the inner wall of a gold hohlraum. The colors inside the hohlraum wall indicate laser
intensity in units of watts per cm 2 . In the 15-MeV radiographs shown here (recorded at
different times during laser drive) the capsule is in the center, the gold hohlraum is the
light-colored outer ring, and the patterns between capsule and hohlraum are due to
electromagnetic fields and plasma jets. This work is discussed in Science, vol. 327, page
1231 (2010). Photo/LLE
very compact, a number of them are utilized simultaneously
at different directions around the
capsules for measuring the symmetry of capsule
compression at both shock bang time and compression
bang time. A third diagnostic is being
developed to measure the precise times corresponding
to shock and compression bang. This
is a proton time-of-flight detector, which utilizes
a special kind of diamond to measure the time
evolution of the fusion-proton fluence at a detector
location.
In addition to using charged fusion products to
study the dynamics of imploded ICF fuel capsules
(including cryogenic fuel capsules) during ex-
periments by LLE researchers, MIT scientists have
performed a wide range of their own important
experiments at LLE this year. One particularly important
series of MIT experiments involved the use
of monoenergetic, charged-particle radiography
to study electric and magnetic fields and plasma
flow in indirect-drive ICF experiments. These are
scaled-down versions of experiments to be performed
at the NIF (laser beams incident on the
inner walls of a small container called a hohlraum
generate x-rays that cause an ICF fuel capsule to
implode). Several papers about this work were
published in Physical Review Letters, and one was
recently published in the journal Science.
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