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C
National Ignition Facility
Research on inertial confinement fusion (ICF) and high energy density (HED)
physics has been pursued intensively in the United States for many years. The Na-
tional Ignition Facility (NIF) is being built to move that research program forward
to a demonstration that ICF can be achieved in the laboratory. An additional goal
is to enhance substantially the range of HED states of matter that can be studied
in the laboratory. The NIF, under construction at Lawrence Livermore National
Laboratory (LLNL) in California, will deliver up to 1.8 MJ of ultraviolet light (354
nm wavelength) in 192 convergent laser beams (Figure C.1). The NIF is being
constructed as part of the Stockpile Stewardship Program by the National Nuclear
Security Administration (NNSA) to ensure the safety, security, and reliability of the
nation’s nuclear stockpile without underground nuclear testing. The NIF’s role in
the stewardship program is to provide relevant data for the weapons program and
to test our scientific understanding of the physics of nuclear weapon explosions
through successful fusion ignition experiments in the laboratory. The completion
of the NIF and the beginning of experiments that will lead to full-scale ignition
tests are scheduled for 2009. These ignition experiments, which will utilize the
most highly developed approach of indirectly driven hot spot ignition, will be the
culmination of more than two decades of experimental campaigns that were per-
formed at the Nova laser at LLNL (the predecessor of the NIF), the OMEGA laser
at the University of Rochester, the Z-machine at Sandia National Laboratories, the
Nike laser at the Naval Research Laboratory, and other lasers elsewhere. Successful
ignition experiments at the NIF will be a key stepping-stone to inertial fusion as
an energy source.
22
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FIGURE C.1 Rendering of the ~2 MJ National Ignition Facility (NIF) that is currently under construction at LLNL showing the location of various
components and support facilities. When completed, the NIF will be the nation’s highest-power MJ-class HED physics facility; it is being built primarily
for weapons-relevant HED physics research, including ICF. Up to 15 percent of the laser time is planned to be available for basic science experiments.
Courtesy of LLNL.
22
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Plasma science
22
The flagship mission of the NIF is to demonstrate fusion ignition—the com-
bining or “fusing” of two light nuclei to form a new nucleus. The NIF’s powerful
array of lasers is intended to ignite enough fusion reactions in a carefully designed
capsule containing the heavy hydrogen isotopes that constitute the fusion fuel to
produce more fusion energy than the laser energy delivered to the target. The physi-
cal processes involved in ICF and the physics challenges that must be overcome to
achieve ignition are detailed in Chapter 2. The NIF is crucial to the NNSA Stockpile
Stewardship Program because it will be able to create the extreme conditions of
temperature and pressure that exist on Earth only in exploding nuclear weapons
and that are therefore relevant to understanding the operation of our modern
nuclear weapons. Understanding the physics of the ignition process and the dy-
namics of matter under HED conditions, together with the HED materials data that
will be provided by the NIF, will allow supercomputer modeling tools to be used
by our nuclear stewards to assess and certify the aging stockpile without carrying
out actual nuclear tests. For example, NIF experiments will investigate the physics
regimes associated with radiation transport, secondary implosion, and ignition
and will enable testing the consequences for weapons operation of the effects of
aging of some weapon components. Please see Chapter 3 for additional details on
the scientific needs of stockpile stewardship.
Other benefits to stockpile stewardship of the NIF are to help maintain the
skills of present nuclear weapons scientists, who must assess the aging-related
conditions that could compromise the reliability of nuclear weapons, as well as to
attract bright young scientists to the program by offering them the excitement of
working with a world-class laser facility. Finally, the committee notes that the NIF
is to be used for basic science experiments 10-15 percent of the time after 2010.
Although not directly relevant to stockpile stewardship, such use will encourage
cross-fertilization of ideas and transfer of best-practices between HED scientists
at universities and national laboratory scientists and help enhance the database on
HED materials properties, extending it beyond the properties of direct relevance
to weapon scientists.
NATIONAL IgNITION FACILITY TECHNOLOgY
The laser design at the National Ignition Facility (NIF) represented a break
from the master-oscillator power-amplifier architecture that had been used in
previous high power lasers used for ICF research, such as the Shiva or Nova lasers.
This new multipass architecture (see Figure C.2 for a representation of 1 beamline
out of 192) was chosen to increase wall-plug efficiency (from 0.2 percent) and de-
crease cost by building only one type of amplifier component in a more compact
footprint. In this design, light is injected from the preamplifier, passes through the
power amplifier, then makes four passes through the main amplifier and, finally,
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aPPendix c 22
FIGURE C.2 The multipass architecture that is common to all of the 192 beamlines of NIF. There
are four passes through the main amplifier and two passes through the power amplifier. Courtesy of
LLNL.
another pass through the power amplifier and out to the final optics assembly.
This strategy required development of several technologies: full-aperture (40-cm)
optical switches, a full-aperture deformable mirror for wave front correction, full-
aperture potassium dihydrogen phosphate (KDP) frequency conversion crystals,
and full-aperture mirrors and polarizers. The optical switch is a Pockels cell that
is energized by electrodes in the optical path. For this reason plasma electrodes are
used. Providing enough KDP crystals for switches and frequency conversion (from
1.056 µm wavelength light to one-half or one-third of that) required development
of rapid growth techniques; a factor of 6 was achieved. The wall-plug efficiency to
produce the 0.33 µm light to be used for ICF experiments starting in 2009 is about
0.5 percent, much less than is needed for fusion energy but suitable for a research
laser. (For the fusion-energy application, diode-pumped lasers are being developed
so that broadband 10 percent efficient flashlamps pumping neodymium-doped
glass can be replaced by 60-70 percent efficient narrow-band light-emitting diodes
pumping crystals or ceramics. Efficiencies for these laser systems are projected to
be 15-20 percent.)
The NIF, which can produce 4.5 MJ (6 MJ if all possible amplifier glass slabs
are installed) of 1.056 µm (infrared) light (3 MJ at half that wavelength and 1.8 MJ
at one-third that wavelength) has an area of three football fields. The laser energy
can be focused to a 100-µm spot. It was not possible to make the entire NIF laser
bay into a clean room by optical standards. Therefore, individual components are
packaged as line-replaceable-units that are assembled in a clean area and can be
quickly installed in hermetic beam lines. This will also reduce downtime.
The number of high-yield shots will be limited by the time for induced radio-
activity of the chamber to decay (about a week) and the maximum yearly yield of
1,200 MJ specified in the Environmental Impact Statement.
