The achievement of ignition at NIF will spur study of inertial fusion and
fusion/fission as clean, environmentally sustainable forms of energy.
The demonstration of ignition will invigorate development
of ICF for fusion energy production. We expect that target
gains of 100 or more will be required for a viable inertial
fusion power plant. The baseline indirect-drive ignition design
is likely to have a gain of 15 to 20.
There are several approaches for achieving higher fusion
gain, including alternative hot-spot ignition schemes, such as
direct-drive, indirect-drive with frequency doubled (530-nm
wavelength) light, and “fast ignition,” which involves the
coupling of an intense high-energy short-pulse laser emission to a compressed DT fuel core. These approaches couple
more energy to an ignition target on the NIF than the initial
ultraviolet laser design, allowing higher target mass and
higher gain.
Scientists will explore alternative ignition schemes on the
OMEGA laser facility and transfer them to the NIF when
they have achieved a sufficient level of maturity. An example of
recent progress is in the direct-drive concept on OMEGA. In
the figure on the facing page, target performance is plotted in
neutron burn-averaged temperature—areal density space. The
solid curve shows the locus of hydrodynamically equivalent
targets (constant implosion velocity and cold fuel adiabat, a, a
measure of the target compressibility). One-dimensional simulations suggest that target design used in the solid curve will
marginally achieve ignition with 0.5 MJ of NIF drive energy,
greatly increasing the probability of ignition with a 1.5-MJ
NIF drive pulse.
The various circles show the current and expected progress
in direct-drive target performance, with the ultimate goal of
achieving direct-drive ignition on the NIF with a 1.5-MJ laser
pulse (solid blue circle). The orange point represents the highest
cryogenic target performance in 2007, with the red point representing the improvements during 2008. The goal is to produce
the conditions represented by the yellow point on OMEGA in
the next year or two. Attaining this objective would give us confidence that NIF can achieve direct-drive ignition in the future.
The HEPW capabilities at OMEGA and NIF will allow us to
pursue fast ignition feasibility experiments.
For energy production, another possibility is the use of
fission-fusion hybrid strategies, in which a moderate-gain ICF
target has its output multiplied by passing through a fission
blanket. Edward Teller, Hans Bethe and Andrei Sakharov originally discussed such schemes. Rapid progress in the development of high-repetition-rate lasers and the advent of advanced
fusion concepts have made these schemes more attractive. In
general, the achievement of ignition at NIF will spur study
of inertial fusion and fusion/fission as clean, environmentally
sustainable forms of energy.
While the achievement of ignition will be a major accomplishment, the flexibility of the NIF and OMEGA laser
facilities, including HEPW beamlines, will allow an exploration of many unique HED states of matter. It will be possible,
for example, to investigate the properties of high-Z materials at extremely high pressures (~100,000,000 atmospheres).
The HEPW beamlines greatly extend the accessible range
of parameters and diagnostics. High-energy ions, electrons,
and photons are produced in prodigious quantities in HEPW
laser-target interactions, and they can deposit their energy in
secondary targets, isochorically heating them before or after
they are compressed. The high laser-to-hard-X-ray conversion
efficiency allows high-Z materials to be radiographed, enabling,
for example, the observation of the propagation of shock waves
in metals.
Research opportunities in HED physics and ICF are poised
to expand greatly in the next few years. The completion of
the OMEGA EP system at LLE and the NIF at LLNL will
unleash unparalleled experimental capabilities and open new
scientific frontiers for exploration. Achieving ignition on the
NIF will spur exploration of energy concepts that could provide limitless, carbon-free energy for the future. t
R.L. McCrory ( rmcc@lle.rochester.edu) and D.D. Meyerhofer are with the
Laboratory for Laser Energetics, University of Rochester, Roch-
Member ester, N. Y., U.S.A. E.I. Moses and C.J. Keane are with Lawrence
Livermore National Laboratory, Livermore, Calif., U.S.A.
[ References and Resources ]
>> D. Strickland and G. Mourou. “Compression of Amplified Chirped
Optical Pulses,” Opt. Comm. 56( 3), 219 (1985).
>> J.D. Lindl. Inertial Confinement Fusion: The Quest for Ignition and
Energy Gain Using Indirect Drive. New York, Springer-Verlag (1998).
>> Frontiers in High-energy-density physics: The X-Games of Contemporary Science, Washington, D.C., National Academies Press
(2003).
>> “Frontiers for Discovery in High-energy-density physics,” prepared
for the Office of Science and Technology Policy, National Science
and Technology Council Interagency Working Group on the Physics of the Universe and prepared by the National Task Force on
High-energy-density physics (July 20, 2004).
>> M. Tabak et al. “Review of Progress in Fast Ignition,” Phys. Plasmas
12( 5), 057305 (2005).
>> C.A. Haynam et al. Appl. Opt. 46, 3276 (2007).
>> C.D. Zhou and R. Betti. “A Measurable Lawson Criterion and
Hydro-Equivalent Curves for Inertial Confinement Fusion,” Phys.
Plasmas 15( 10), 102707 (2008).
>> E.I. Moses et al. Lawrence Livermore National Laboratory report,
LLLNL-JRNL-4066521. “The National Ignition Facility: Ushering in
a New Age for High Energy Density Science,” Dec. 2008, to be
published in Phys. Plasmas.
>> R.L. McCrory et al. “Progress in Direct-Drive Inertial Confinement
Fusion Research,” Phys. Plasmas 15( 5), 055503 (2008).
