Optics assembly building
Laser bay 1
I
n experiments in high-energy-density (HED)
physics, researchers create some of the most
Target area
extreme conditions available in the labo-
Laser bay 2
ratory, including pressures of 1,000,000
atmospheres and much higher. These conditions are ubiquitous in the natural universe,
from supernovae explosions to astrophysical jets
to planetary interiors. A new generation of laser
Switchyard
facilities places laboratory high-energy-density
physics on the verge of a revolution.
Diagnostics building
HED conditions were originally produced in
nuclear weapons tests. Since the development of
high-power, high-energy lasers in the early 1970s,
this research has also been conducted in the
laboratory. The primary sponsor of this work has
been the Department of Energy’s National Nuclear Security NIF aerial view shows two laser bays with 96 beams each, the
Administration through its Stockpile Stewardship Program.
switchyard, the target chamber area, the diagnostics building and
the optical assembly building.
Over the past decades, the experimental tools that are available for studying extreme conditions have improved, and the
state of the art has expanded to include increasingly energetic lasers and pulsed-power sources (drivers). Being able to
precisely control the driver interaction with the target is more
Laser beams in two rings
important than total energy in creating and understanding
HED plasma conditions.
The Nova laser at Lawrence Livermore National Laboratory
(LLNL) was completed in 1984, and then decommissioned in
1999, while the 60-beam OMEGA laser system at the Uni-
5. 7 mm
1. 1 mm
Capsule
versity of Rochester’s Laboratory for Laser Energetics (LLE)
Hohlraum wall:
was finished in 1995. These lasers developed the precision high Z
control and flexibility needed to generate a wide variety of
Hohlraum fill
HED conditions. Two new facilities, the OMEGA Extended
low pressure He/H
Performance (OMEGA EP) laser system at LLE (completed
April 2008) and the National Ignition Facility (NIF) at LLNL
Laser entrance hole
(completed March 2009) will significantly extend the range
of HED plasma conditions that can be created and studied in
the laboratory.
The NIF will produce up to 1. 8 MJ of 351-nm laser light—
which is higher than that produced by any previous laser system by a factor of 50. The OMEGA EP laser system includes
two high-energy petawatt laser beams that will each produce
2. 6 kJ of 1,053-nm laser light in 10-ps pulses, an increase over
previous short-pulse systems by a factor of about five.
We expect to achieve inertial confinement fusion (ICF)
ignition on the NIF in the next couple of years; this will be the
culmination of a decades-long quest to demonstrate controlled
thermonuclear ignition in the laboratory. The ICF concept
for thermonuclear ignition involves the radial compression
of a spherical shell of deuterium-tritium (DT) ice by a factor
of roughly 30 with an HED driver. This ice layer is enclosed
within a spherical ablator (capsule). The ablator absorbs the
driver energy, either directly (direct-drive), or through X-rays
obtained by the driver interacting with a high-atomic-number
(Z) material inside an X-ray radiation enclosure such as an
X-ray oven or hohlraum (indirect drive).
Ablator
(Be/Cu or
CH/Ge)
DT ice
DT gas fill
As the ablator material is heated, it expands from the target
surface. By conservation of momentum (rocket effect), the
remaining target material is radially compressed to the extreme
temperature and density conditions required to achieve ignition. A hot spot forms in the center of the compressed target
with temperatures of roughly 50,000,000 degrees (C).
The deuterium and tritium ions begin to undergo nuclear
fusion, D+T —> n ( 14. 1 MeV) + He ( 3. 5 MeV), where n sym-
2+
bolizes a neutron. If the product of the density and the radius
of the hot spot is greater than 0.3 g/cm , the He (alpha-par-
2 2+
ticle) energy is deposited in the DT fuel and a thermonuclear
burn wave begins to propagate. The total neutron energy
produced depends on the product of the density and thickness
of the cold fuel region surrounding the hot spot formed by
the compression of the solid DT shell.
In the initial NIF experiments, we anticipate that approximately a third of the cold shell material will fuse, producing a
total neutron energy output that is 10 to 20 times that of the
